Bivalvia, commonly referred to as bivalves, are the class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts. They include clams, oysters, mussels, scallops, and numerous other families. The majority are filter feeders and have no head orradula. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment on the seabed, where they are safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. A few bore into wood, clay or stone and live inside these substances. Some bivalves, such as the scallops, can swim.
The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. These are joined together along one edge by a flexible ligament that, in conjunction with interlocking “teeth” on each of the valves, forms the hinge. This arrangement allows the shell to be opened and closed without the two halves becoming disarticulated. The shell is typically bilaterally symmetrical, with the hinge lying in the sagittal plane. Adult shell sizes vary from fractions of a millimetre to over a metre in length, but the majority of species do not exceed 10 cm (4 in).
Bivalves vary greatly in overall shape. Some, such as the cockles, are nearly globular and can jump by bending and straightening the foot. Others, such as the razor clams, are burrowing specialists with elongated shells and powerful feet for digging. The shipworms of the family Teredinidae have greatly elongated bodies, but the shell valves are much reduced and restricted to the anterior end of the body, where they function as scraping organs that permit the animal to dig tunnels through wood.[9]
Near the hinge of the shell is the umbone or beak, a rounded, knobbly protuberance. This represents the oldest portion of the shell, with extra material later being laid down along the margins on the opposite side. The hinge area is the dorsal region of the shell and the lower margin is the ventral region. The anterior or front of the shell is where the byssus and foot are located, and the posterior of the shell is where the siphons are located. When the umbone is uppermost, the valve with the anterior end to the left is considered to be the left valve, while the valve with the anterior end to the right is the right valve.[10]
In all molluscs, the mantle forms a thin membrane covering the animal’s body and extending out from it in flaps or lobes. In bivalves, the mantle lobes secrete the valves, and the mantle crest secretes the whole hinge mechanism consisting of ligament, byssus threads, and teeth.[11]
Visible on the inside of most empty bivalve valves is a shiny line that runs parallel to the outer margin of the shell and often connects the two adductor muscle scars. This line (known as the pallial line) exists because parallel to the opening edge of the bivalve’s shell, the mantle is attached to the shell by a continuous narrow row of minute mantle retractor muscles. The function of these small muscles is to pull the loose edge of the mantle up out of harm’s way when this is necessary because of minor predation attempts. In many bivalves, the mantle edges fuse at the posterior end of the shell to form two siphons, through which water is inhaled and expelled for respiration and suspension feeding.[10] There is a pocket-like space into which the siphons fit when they are retracted. This is visible on the inside of the valve as an indentation on the pallial line which is known as the pallial sinus.[10]
The shell is composed of two calcareous valves held together by a ligament. The valves are made of either calcite, as is the case in oysters, or both calcite and aragonite. Sometimes the aragonite forms an inner, nacreous layer, as is the case in the order Pterioida. In other taxa, alternate layers of calcite and aragonite are laid down.[12] The ligament and byssus, if calcified, are composed of aragonite.[12] The outermost layer of the shell is theperiostracum, a skin-like layer which is composed of a horny organic substance. The periostracum is secreted in the groove between the outer and middle layers of the mantle, and is usually olive or brown in colour and easily abraded.[13] The outer surface of the valves is often sculpted with clams having fine concentric striations, scallops radial ribs and oysters a latticework of irregular markings.[14]
The shell is added to in two ways; the valves grow larger when more material is secreted by the mantle at the margin of the shell, and the valves themselves thicken gradually throughout the animal’s life as more calcareous matter is secreted by the mantle lobes. The two valves are held together at a hinge joint by a ligament composed of two keratinised proteins, tensilium and resilium. In different groups of bivalves the ligament can be internal or external in position. The main function of the ligament (as well as joining the valves together) is to passively cause the shell to open. The shell is actively closed using the adductor muscle or muscles attached to the inner surface of both valves. The position of the muscles is often clearly visible on the inside of empty valves as circular or oval muscle scars. Along the hinge line of the shell there are often a number of hinge teeth which prevent the valves from moving laterally relative to one another. The arrangement of these teeth is often important in identifying bivalves.[16]
The sensory organs of bivalves are not well developed and are largely located on the posterior mantle margins. The organs are usually mechanoreceptors or chemoreceptors located in shorttentacles. The chemoreceptor cells taste the water and are sensitive to touch. They are typically found near the siphons, but in some species may fringe the entire mantle cavity.[18] Theosphradium is a patch of sensory cells located below the posterior adductor muscle that may serve to taste the water or measure its turbidity, but is probably not homologous with the structure of the same name found in snails and slugs.[19] Statocysts within the organism help the bivalve to sense and correct its orientation. Each statocyst consists of a small sac lined with sensory cilia that detects the movement of a mineral mass, a statolith, under gravity.[20][21] In the order Anomalodesmata, the inhalant siphon is surrounded by vibration-sensitive tentacles for detecting prey.[22]
Many bivalves have no eyes, but a few members of Arcoidea, Limopsoidea, Mytiloidea, Anomioidea, Ostreoidea and Limoidea have simple eyes on the margin of the mantle. These consist of a pit of photo-sensory cells and a lens.[23] Scallops have more complex eyes with a lens, a two-layered retina and a concave mirror.[24] All bivalves have light-sensitive cells that can detect a shadow falling over the animal.[17]
The main muscular system in bivalves is the posterior and anterior adductor muscles, although the anterior muscles may be reduced or even lost in some species. These strong muscles connect the two valves and contract in order to close the shell. They work in opposition to the ligament which tends to pull the valves apart.[16] In sedentary or recumbent bivalves that lie on one valve, such as the oysters and scallops, the anterior adductor muscle has been lost and the posterior muscle is positioned centrally. In file shells that can swim by flapping their valves, there is also a single, central adductor muscle.[13] These muscles are composed of two types of muscle fibre, striated muscle bundles for fast actions and smooth muscle bundles for maintaining a steady pull.[13]
The mantle suspender muscles attach the mantle to the shell and leave an arc-shaped scar on the inside of the valve, the pallial line. The paired pedal protractor and retractor muscles operate the animal’s foot. Some bivalves, such as oysters and most scallops, are unable to extend their foot and in them, these muscles are absent. Other paired muscles control the siphons and the byssus.[10][13]
Most bivalves are filter feeders, using their gills to capture particulate food such as phytoplankton from the water. The Protobranchs feed in a different way, scraping detritus from the seabed, and this may be the original mode of feeding used by all bivalves before the gills became adapted for filter feeding. These primitive bivalves hold onto the substratum with a pair of tentacles at the edge of the mouth, each of which has a single palp, or flap. The tentacles are covered in mucus, which traps the food, and cilia, which transport the particles back to the palps. These then sort the particles, rejecting those that are unsuitable or too large to digest, and conveying others to the mouth.[20]
In the Filibranchia and Eulamellibranchia, water is drawn into the shell from the posterior ventral surface of the animal, passes upwards through the gills and doubles back to be expelled just above the intake. In burrowing species, there may be two elongated, retractable siphons reaching up to the seabed, one each for the inhalant and exhalant streams of water. The gills of filter-feeding bivalves are known as ctenidia and have become highly modified to increase their ability to capture food. For example, the cilia on the gills, which originally served to remove unwanted sediment, have become adapted to capture food particles, and transport them in a steady stream of mucus to the mouth. The filaments of the gills are also much longer than those in more primitive bivalves, and are folded over to create a groove through which food can be transported. The structure of the gills varies considerably, and can serve as a useful means for classifying bivalves into groups.[28]
A few bivalves, such as the granular poromya (Poromya granulata), are carnivorous, eating much larger prey than the tiny microalgae consumed by other bivalves. In these animals, the gills are relatively small, and form a perforated barrier separating the main mantle cavity from a smaller chamber through which the water is exhaled. Muscles draw water in through the inhalant siphon which is modified into a cowl-shaped organ, sucking in small crustaceans and worms at the same time. The siphon can be retracted quickly and inverted, bringing the prey within reach of the mouth. The gut is modified so that large food particles can be digested.[27]
The sexes are usually separate in bivalves but some hermaphroditism is known. The gonads are located close to the intestines, and either open into the nephridia, or through a separate pore into the mantle cavity.[33] The ripe gonads of male and females release sperm and eggs into the water column. Spawning may take place continually or be triggered by environmental factors such as day length, water temperature or the presence of sperm in the water. Some species are “dribble spawners” but others release their gametes in batches or all at once. Mass spawning events sometimes take place when all the bivalves in an area synchronise their release of spawn.[34]
Fertilization is usually external. Typically, there is a short stage lasting a few hours or days before the eggs hatch into trochophore larvae. These later develop into veliger larvae which settle on the seabed and undergo metamorphosis into juveniles known as spat.[33] In some species, such as those in the genus Lasaea, females draw water containing sperm in through their inhalant siphons and fertilisation is inside the female. These species then brood the young inside their mantle cavity, eventually releasing them into the water column as veliger larvae or as crawl-away juveniles.[35]
The bivalves are a highly successful class of invertebrates found in aquatic habitats throughout the world. Most are infaunal and live buried in sediment on the seabed, or in the sediment in freshwater habitats. A large number of bivalve species are found in the intertidal and sublittoral zones of the oceans. A sandy sea beach may superficially appear to be devoid of life, but there is often a very large number of bivalves and other invertebrates living beneath the surface of the sand. On a large beach in South Wales, careful sampling produced an estimate of 1.44 million cockles (Cerastoderma edule) per acre of beach.[50]
Bivalves inhabit the tropics as well as temperate and boreal waters. A number of species can survive and even flourish in extreme conditions. They are abundant in the Arctic, about 140 species being known from that zone.[51] The Antarctic scallop, Adamussium colbecki, lives under the sea ice at the other end of the globe, where the sub-zero temperatures mean that growth rates are very slow.[52] The giant mussel, Bathymodiolus thermophilus, and the giant white clam, Calyptogena magnifica, both live clustered around hydrothermal vents at abyssal depths in the Pacific Ocean. They havechemosymbiotic bacteria in their gills that oxidise hydrogen sulphide, and the molluscs absorb nutrients synthesized by these bacteria.[53] The saddle oyster, Enigmonia aenigmatica, is a marine species that could be considered amphibious. It lives above the high tide mark in the tropical Indo-Pacific on the underside of mangrove leaves, on mangrove branches and on sea walls in the splash zone.[54]
Most bivalves adopt a sedentary or even sessile life style, often spending their whole lives in the area in which they first settled as juveniles. The majority of bivalves are infaunal, living under the seabed, buried in soft substrates such as sand, silt, mud, gravel or coral fragments. Many of these live in the intertidal zone where the sediment remains damp even when the tide is out. When buried in the sediment, burrowing bivalves are protected from the pounding of waves, desiccation and overheating during low tide, and variations in salinity caused by rainwater. They are also out of the reach of many predators.[58] Their general strategy is to extend their siphons to the surface for feeding and respiration during high tide, but to descend to greater depths or keep their shell tightly shut when the tide goes out.[58] They use their muscular foot to dig into the substrate. Other bivalves, such as mussels, attach themselves to hard surfaces using tough byssus threads made of keratin and proteins. They are more exposed to attack by predators than the burrowing bivalves. Some bivalves, including the true oysters, the jewel boxes, the jingle shells, the thorny oysters and the kitten’s paws, cement themselves to stones, rock or larger dead shells.[61] In oysters the lower valve may be almost flat while the upper valve develops layer upon layer of thin horny material reinforced with calcium carbonate. Oysters sometimes occur in dense beds in the neritic zoneand, like most bivalves, are filter feeders.[16]
Razor shells can dig themselves into the sand with great speed to escape predation. When a Pacific razor clam (Siliqua patula) is laid on the surface of the beach it can bury itself completely in seven seconds [70] and the Atlantic jackknife clam, Ensis directus, can do the same within fifteen seconds.[71] Scallops and file clams can swim by opening and closing their valves rapidly; water is ejected on either side of the hinge area and they move with the flapping valves in front.[72] Scallops have simple eyes around the margin of the mantle and can clap their valves shut to move sharply, hinge first, to escape from danger.[72] Cockles can use their foot to move across the seabed or leap away from threats. The foot is first extended before being contracted suddenly when it acts like a spring, projecting the animal forwards.[73]
In many bivalves that have siphons, they can be retracted back into the safety of the shell. If the siphons inadvertently get attacked by a predator, they snap off. The animal can regenerate them later, a process that starts when the cells close to the damaged site become activated and remodel the tissue back to its pre-existing form and size.[74]
File shells such as Limaria fragilis can produce a noxious secretion when stressed. It has numerous tentacles which fringe its mantle and protrude some distance from the shell when it is feeding. If attacked, it sheds tentacles in a process known as autotomy. The toxin released by this is distasteful and the detached tentacles continue to writhe which may also serve to distract potential predators.[75]
Notes from Wikipedia. For more details: http://en.wikipedia.org/wiki/Bivalvia
![Various types of sea anemone
Photos by Sergio Discepolo
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria.
A sea anemone is a polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column shaped body ending in an oral disc. Most are from 1.8 to 3 centimetres (0.71 to 1.2 in) in diameter, but anemones as small as 4 millimetres (0.16 in) or as large as nearly 2 metres (6.6 ft) are known.They can have anywhere from a few tens to a few hundred tentacles.
The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins), an inner filament, and an external sensory hair. When the hair is touched it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of venom in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. The sea anemone eats small fish and shrimp.
The venom is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which are the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators]. Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone’s sting and shelter themselves from predators within its tentacles.
Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location. Most sea anemones attach temporarily to submerged objects; a few thrust themselves into the sand or live in burrows; a few are parasitic on other marine organisms and some have symbiotic relationships with hermit crabs.
Notes from Wikipedia](http://24.media.tumblr.com/810a2e026a0d97a8e4e7e8c1bed7fc4b/tumblr_mgz1l8wBPF1rw22b7o1_500.jpg)
![Various types of sea anemone
Photos by Sergio Discepolo
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria.
A sea anemone is a polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column shaped body ending in an oral disc. Most are from 1.8 to 3 centimetres (0.71 to 1.2 in) in diameter, but anemones as small as 4 millimetres (0.16 in) or as large as nearly 2 metres (6.6 ft) are known.They can have anywhere from a few tens to a few hundred tentacles.
The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins), an inner filament, and an external sensory hair. When the hair is touched it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of venom in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. The sea anemone eats small fish and shrimp.
The venom is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which are the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators]. Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone’s sting and shelter themselves from predators within its tentacles.
Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location. Most sea anemones attach temporarily to submerged objects; a few thrust themselves into the sand or live in burrows; a few are parasitic on other marine organisms and some have symbiotic relationships with hermit crabs.
Notes from Wikipedia](http://25.media.tumblr.com/69834648e467262499dbc901d5b1b7d8/tumblr_mgz1l8wBPF1rw22b7o2_500.jpg)
![Various types of sea anemone
Photos by Sergio Discepolo
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria.
A sea anemone is a polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column shaped body ending in an oral disc. Most are from 1.8 to 3 centimetres (0.71 to 1.2 in) in diameter, but anemones as small as 4 millimetres (0.16 in) or as large as nearly 2 metres (6.6 ft) are known.They can have anywhere from a few tens to a few hundred tentacles.
The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins), an inner filament, and an external sensory hair. When the hair is touched it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of venom in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. The sea anemone eats small fish and shrimp.
The venom is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which are the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators]. Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone’s sting and shelter themselves from predators within its tentacles.
Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location. Most sea anemones attach temporarily to submerged objects; a few thrust themselves into the sand or live in burrows; a few are parasitic on other marine organisms and some have symbiotic relationships with hermit crabs.
Notes from Wikipedia](http://25.media.tumblr.com/6a77bf6024fcacd6b611b5f65a94cc1c/tumblr_mgz1l8wBPF1rw22b7o3_500.jpg)
![Various types of sea anemone
Photos by Sergio Discepolo
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria.
A sea anemone is a polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column shaped body ending in an oral disc. Most are from 1.8 to 3 centimetres (0.71 to 1.2 in) in diameter, but anemones as small as 4 millimetres (0.16 in) or as large as nearly 2 metres (6.6 ft) are known.They can have anywhere from a few tens to a few hundred tentacles.
The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins), an inner filament, and an external sensory hair. When the hair is touched it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of venom in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. The sea anemone eats small fish and shrimp.
The venom is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which are the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators]. Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone’s sting and shelter themselves from predators within its tentacles.
Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location. Most sea anemones attach temporarily to submerged objects; a few thrust themselves into the sand or live in burrows; a few are parasitic on other marine organisms and some have symbiotic relationships with hermit crabs.
Notes from Wikipedia](http://25.media.tumblr.com/b7633ba8619bab975c08666cc916b357/tumblr_mgz1l8wBPF1rw22b7o4_500.jpg)
![Various types of sea anemone
Photos by Sergio Discepolo
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria.
A sea anemone is a polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column shaped body ending in an oral disc. Most are from 1.8 to 3 centimetres (0.71 to 1.2 in) in diameter, but anemones as small as 4 millimetres (0.16 in) or as large as nearly 2 metres (6.6 ft) are known.They can have anywhere from a few tens to a few hundred tentacles.
The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins), an inner filament, and an external sensory hair. When the hair is touched it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of venom in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. The sea anemone eats small fish and shrimp.
The venom is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which are the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators]. Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone’s sting and shelter themselves from predators within its tentacles.
Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location. Most sea anemones attach temporarily to submerged objects; a few thrust themselves into the sand or live in burrows; a few are parasitic on other marine organisms and some have symbiotic relationships with hermit crabs.
Notes from Wikipedia](http://24.media.tumblr.com/2beca2f1f648ad63da22ea92ea8c9ef5/tumblr_mgz1l8wBPF1rw22b7o5_500.jpg)
![Various types of sea anemone
Photos by Sergio Discepolo
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria.
A sea anemone is a polyp attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, with a column shaped body ending in an oral disc. Most are from 1.8 to 3 centimetres (0.71 to 1.2 in) in diameter, but anemones as small as 4 millimetres (0.16 in) or as large as nearly 2 metres (6.6 ft) are known.They can have anywhere from a few tens to a few hundred tentacles.
The mouth, also the anus of the sea anemone, is in the middle of the oral disc surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name. The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins), an inner filament, and an external sensory hair. When the hair is touched it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of venom in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. The sea anemone eats small fish and shrimp.
The venom is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which are the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators]. Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone’s sting and shelter themselves from predators within its tentacles.
Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location. Most sea anemones attach temporarily to submerged objects; a few thrust themselves into the sand or live in burrows; a few are parasitic on other marine organisms and some have symbiotic relationships with hermit crabs.
Notes from Wikipedia](http://24.media.tumblr.com/921557602875292524b1ef36f77369f8/tumblr_mgz1l8wBPF1rw22b7o6_500.jpg)
![Nudibranch Nembrotha chamberlaini - Puerto Galera Philippines
By Sergio Discepolo 2010
Nembrotha chamberlaini is a species of colorful sea slug, a dorid nudibranch, a marine gastropod mollusk in the family Polyceridae. It was first described in 1997.[2]
This species is known only from the Philippines and Indonesia. [2]
Nembrotha chamberlaini is white with streaks of black and occasionally yellow splashed across the upper mantle. It has very distinctive bright red gillsand rhinophores. The foot and mouth parts are typically light-purple. This nudibranch has a very characteristic color pattern which is typical of species that display warning coloration to other species.
Nembrotha chamberlaini is easily confused with Nembrotha aurea and Nembrotha purpureolineata. All three species have a similar range of color variation although N. aurea often has orange patches not present in Nembrotha chamberlaini.
N. chamberlaini can reach a length of 100 mm.
This species feeds on ascidians and tunicates. It has been seen feeding on the bright-blue ascidian, Rhopalaea sp, as well as other ascidians Clavelina sp., & Oxycorynia sp. .[2]
Notes from Wikipedia](http://25.media.tumblr.com/5895b639843cbcffa1d24eaff59fb126/tumblr_metay8CxX91rw22b7o1_500.jpg)
![Stenorhynchus seticornis, the yellowline arrow crab or simply arrow crab, is a species of marine crab.
by Sergio Discepolo 2006
The body of S. seticornis is triangular, and the rostrum is drawn out into a long point with serrate edges.[1]The legs are also long and thin, up to 10 cm (3.9 in) across,[2] and the animal’s carapace may be up to 6 cm (2.4 in) long.[3] Colouration is variable in this species; the body may be golden, yellow or cream, marked with brown, black or iridescent-blue lines; the legs are reddish or yellow, and the claws are blue or violet.[3]
Stenorhynchus seticornis is found in the western Atlantic Ocean, from North Carolina and Bermuda to Brazil, including throughout the Caribbean Sea.[3] It lives on coral reefs at depths of 10–30 feet (3.0–9.1 m).[4]
S. seticornis is nocturnal and territorial.[5] It eats small feather duster worms and other coral reefinvertebrates. [5] This crab is commonly kept in reef aquariums to control bristle worm populations.[6]
S. seticornis is one of a number of different invertebrates that are found living in association with the sea anemone, Lebrunia danae. It is often found among the anemone’s pseudotentacles along with Pederson’s cleaning shrimp (Ancylomenes pedersoni) and the spotted cleaner shrimp (Periclimenes yucatanicus).[7]
During mating, the male places a spermatophore on the female, which she uses to fertilise her eggs. These fertilised eggs are then carried on the female’s pleopods until they are ready to hatch into zoea larvae.[5] These swim towards the ocean surface and feed on plankton. They grow through a series of moults, and eventually metamorphose into the adult form.[5]
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_melxcbaVjL1rw22b7o1_500.jpg)
![Stenorhynchus seticornis, the yellowline arrow crab or simply arrow crab, is a species of marine crab.
by Sergio Discepolo 2006
The body of S. seticornis is triangular, and the rostrum is drawn out into a long point with serrate edges.[1]The legs are also long and thin, up to 10 cm (3.9 in) across,[2] and the animal’s carapace may be up to 6 cm (2.4 in) long.[3] Colouration is variable in this species; the body may be golden, yellow or cream, marked with brown, black or iridescent-blue lines; the legs are reddish or yellow, and the claws are blue or violet.[3]
Stenorhynchus seticornis is found in the western Atlantic Ocean, from North Carolina and Bermuda to Brazil, including throughout the Caribbean Sea.[3] It lives on coral reefs at depths of 10–30 feet (3.0–9.1 m).[4]
S. seticornis is nocturnal and territorial.[5] It eats small feather duster worms and other coral reefinvertebrates. [5] This crab is commonly kept in reef aquariums to control bristle worm populations.[6]
S. seticornis is one of a number of different invertebrates that are found living in association with the sea anemone, Lebrunia danae. It is often found among the anemone’s pseudotentacles along with Pederson’s cleaning shrimp (Ancylomenes pedersoni) and the spotted cleaner shrimp (Periclimenes yucatanicus).[7]
During mating, the male places a spermatophore on the female, which she uses to fertilise her eggs. These fertilised eggs are then carried on the female’s pleopods until they are ready to hatch into zoea larvae.[5] These swim towards the ocean surface and feed on plankton. They grow through a series of moults, and eventually metamorphose into the adult form.[5]
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_melxcbaVjL1rw22b7o2_500.jpg)
![Stenorhynchus seticornis, the yellowline arrow crab or simply arrow crab, is a species of marine crab.
by Sergio Discepolo 2006
The body of S. seticornis is triangular, and the rostrum is drawn out into a long point with serrate edges.[1]The legs are also long and thin, up to 10 cm (3.9 in) across,[2] and the animal’s carapace may be up to 6 cm (2.4 in) long.[3] Colouration is variable in this species; the body may be golden, yellow or cream, marked with brown, black or iridescent-blue lines; the legs are reddish or yellow, and the claws are blue or violet.[3]
Stenorhynchus seticornis is found in the western Atlantic Ocean, from North Carolina and Bermuda to Brazil, including throughout the Caribbean Sea.[3] It lives on coral reefs at depths of 10–30 feet (3.0–9.1 m).[4]
S. seticornis is nocturnal and territorial.[5] It eats small feather duster worms and other coral reefinvertebrates. [5] This crab is commonly kept in reef aquariums to control bristle worm populations.[6]
S. seticornis is one of a number of different invertebrates that are found living in association with the sea anemone, Lebrunia danae. It is often found among the anemone’s pseudotentacles along with Pederson’s cleaning shrimp (Ancylomenes pedersoni) and the spotted cleaner shrimp (Periclimenes yucatanicus).[7]
During mating, the male places a spermatophore on the female, which she uses to fertilise her eggs. These fertilised eggs are then carried on the female’s pleopods until they are ready to hatch into zoea larvae.[5] These swim towards the ocean surface and feed on plankton. They grow through a series of moults, and eventually metamorphose into the adult form.[5]
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_melxcbaVjL1rw22b7o3_500.jpg)
![Bivalvia, commonly referred to as bivalves, are the class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts. They include clams, oysters, mussels, scallops, and numerous other families. The majority are filter feeders and have no head orradula. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment on the seabed, where they are safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. A few bore into wood, clay or stone and live inside these substances. Some bivalves, such as the scallops, can swim.
The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. These are joined together along one edge by a flexible ligament that, in conjunction with interlocking “teeth” on each of the valves, forms the hinge. This arrangement allows the shell to be opened and closed without the two halves becoming disarticulated. The shell is typically bilaterally symmetrical, with the hinge lying in the sagittal plane. Adult shell sizes vary from fractions of a millimetre to over a metre in length, but the majority of species do not exceed 10 cm (4 in).
Bivalves vary greatly in overall shape. Some, such as the cockles, are nearly globular and can jump by bending and straightening the foot. Others, such as the razor clams, are burrowing specialists with elongated shells and powerful feet for digging. The shipworms of the family Teredinidae have greatly elongated bodies, but the shell valves are much reduced and restricted to the anterior end of the body, where they function as scraping organs that permit the animal to dig tunnels through wood.[9]
Near the hinge of the shell is the umbone or beak, a rounded, knobbly protuberance. This represents the oldest portion of the shell, with extra material later being laid down along the margins on the opposite side. The hinge area is the dorsal region of the shell and the lower margin is the ventral region. The anterior or front of the shell is where the byssus and foot are located, and the posterior of the shell is where the siphons are located. When the umbone is uppermost, the valve with the anterior end to the left is considered to be the left valve, while the valve with the anterior end to the right is the right valve.[10]
In all molluscs, the mantle forms a thin membrane covering the animal’s body and extending out from it in flaps or lobes. In bivalves, the mantle lobes secrete the valves, and the mantle crest secretes the whole hinge mechanism consisting of ligament, byssus threads, and teeth.[11]
Visible on the inside of most empty bivalve valves is a shiny line that runs parallel to the outer margin of the shell and often connects the two adductor muscle scars. This line (known as the pallial line) exists because parallel to the opening edge of the bivalve’s shell, the mantle is attached to the shell by a continuous narrow row of minute mantle retractor muscles. The function of these small muscles is to pull the loose edge of the mantle up out of harm’s way when this is necessary because of minor predation attempts. In many bivalves, the mantle edges fuse at the posterior end of the shell to form two siphons, through which water is inhaled and expelled for respiration and suspension feeding.[10] There is a pocket-like space into which the siphons fit when they are retracted. This is visible on the inside of the valve as an indentation on the pallial line which is known as the pallial sinus.[10]
The shell is composed of two calcareous valves held together by a ligament. The valves are made of either calcite, as is the case in oysters, or both calcite and aragonite. Sometimes the aragonite forms an inner, nacreous layer, as is the case in the order Pterioida. In other taxa, alternate layers of calcite and aragonite are laid down.[12] The ligament and byssus, if calcified, are composed of aragonite.[12] The outermost layer of the shell is theperiostracum, a skin-like layer which is composed of a horny organic substance. The periostracum is secreted in the groove between the outer and middle layers of the mantle, and is usually olive or brown in colour and easily abraded.[13] The outer surface of the valves is often sculpted with clams having fine concentric striations, scallops radial ribs and oysters a latticework of irregular markings.[14]
The shell is added to in two ways; the valves grow larger when more material is secreted by the mantle at the margin of the shell, and the valves themselves thicken gradually throughout the animal’s life as more calcareous matter is secreted by the mantle lobes. The two valves are held together at a hinge joint by a ligament composed of two keratinised proteins, tensilium and resilium. In different groups of bivalves the ligament can be internal or external in position. The main function of the ligament (as well as joining the valves together) is to passively cause the shell to open. The shell is actively closed using the adductor muscle or muscles attached to the inner surface of both valves. The position of the muscles is often clearly visible on the inside of empty valves as circular or oval muscle scars. Along the hinge line of the shell there are often a number of hinge teeth which prevent the valves from moving laterally relative to one another. The arrangement of these teeth is often important in identifying bivalves.[16]
The sensory organs of bivalves are not well developed and are largely located on the posterior mantle margins. The organs are usually mechanoreceptors or chemoreceptors located in shorttentacles. The chemoreceptor cells taste the water and are sensitive to touch. They are typically found near the siphons, but in some species may fringe the entire mantle cavity.[18] Theosphradium is a patch of sensory cells located below the posterior adductor muscle that may serve to taste the water or measure its turbidity, but is probably not homologous with the structure of the same name found in snails and slugs.[19] Statocysts within the organism help the bivalve to sense and correct its orientation. Each statocyst consists of a small sac lined with sensory cilia that detects the movement of a mineral mass, a statolith, under gravity.[20][21] In the order Anomalodesmata, the inhalant siphon is surrounded by vibration-sensitive tentacles for detecting prey.[22]
Many bivalves have no eyes, but a few members of Arcoidea, Limopsoidea, Mytiloidea, Anomioidea, Ostreoidea and Limoidea have simple eyes on the margin of the mantle. These consist of a pit of photo-sensory cells and a lens.[23] Scallops have more complex eyes with a lens, a two-layered retina and a concave mirror.[24] All bivalves have light-sensitive cells that can detect a shadow falling over the animal.[17]
The main muscular system in bivalves is the posterior and anterior adductor muscles, although the anterior muscles may be reduced or even lost in some species. These strong muscles connect the two valves and contract in order to close the shell. They work in opposition to the ligament which tends to pull the valves apart.[16] In sedentary or recumbent bivalves that lie on one valve, such as the oysters and scallops, the anterior adductor muscle has been lost and the posterior muscle is positioned centrally. In file shells that can swim by flapping their valves, there is also a single, central adductor muscle.[13] These muscles are composed of two types of muscle fibre, striated muscle bundles for fast actions and smooth muscle bundles for maintaining a steady pull.[13]
The mantle suspender muscles attach the mantle to the shell and leave an arc-shaped scar on the inside of the valve, the pallial line. The paired pedal protractor and retractor muscles operate the animal’s foot. Some bivalves, such as oysters and most scallops, are unable to extend their foot and in them, these muscles are absent. Other paired muscles control the siphons and the byssus.[10][13]
Most bivalves are filter feeders, using their gills to capture particulate food such as phytoplankton from the water. The Protobranchs feed in a different way, scraping detritus from the seabed, and this may be the original mode of feeding used by all bivalves before the gills became adapted for filter feeding. These primitive bivalves hold onto the substratum with a pair of tentacles at the edge of the mouth, each of which has a single palp, or flap. The tentacles are covered in mucus, which traps the food, and cilia, which transport the particles back to the palps. These then sort the particles, rejecting those that are unsuitable or too large to digest, and conveying others to the mouth.[20]
In the Filibranchia and Eulamellibranchia, water is drawn into the shell from the posterior ventral surface of the animal, passes upwards through the gills and doubles back to be expelled just above the intake. In burrowing species, there may be two elongated, retractable siphons reaching up to the seabed, one each for the inhalant and exhalant streams of water. The gills of filter-feeding bivalves are known as ctenidia and have become highly modified to increase their ability to capture food. For example, the cilia on the gills, which originally served to remove unwanted sediment, have become adapted to capture food particles, and transport them in a steady stream of mucus to the mouth. The filaments of the gills are also much longer than those in more primitive bivalves, and are folded over to create a groove through which food can be transported. The structure of the gills varies considerably, and can serve as a useful means for classifying bivalves into groups.[28]
A few bivalves, such as the granular poromya (Poromya granulata), are carnivorous, eating much larger prey than the tiny microalgae consumed by other bivalves. In these animals, the gills are relatively small, and form a perforated barrier separating the main mantle cavity from a smaller chamber through which the water is exhaled. Muscles draw water in through the inhalant siphon which is modified into a cowl-shaped organ, sucking in small crustaceans and worms at the same time. The siphon can be retracted quickly and inverted, bringing the prey within reach of the mouth. The gut is modified so that large food particles can be digested.[27]
The sexes are usually separate in bivalves but some hermaphroditism is known. The gonads are located close to the intestines, and either open into the nephridia, or through a separate pore into the mantle cavity.[33] The ripe gonads of male and females release sperm and eggs into the water column. Spawning may take place continually or be triggered by environmental factors such as day length, water temperature or the presence of sperm in the water. Some species are “dribble spawners” but others release their gametes in batches or all at once. Mass spawning events sometimes take place when all the bivalves in an area synchronise their release of spawn.[34]
Fertilization is usually external. Typically, there is a short stage lasting a few hours or days before the eggs hatch into trochophore larvae. These later develop into veliger larvae which settle on the seabed and undergo metamorphosis into juveniles known as spat.[33] In some species, such as those in the genus Lasaea, females draw water containing sperm in through their inhalant siphons and fertilisation is inside the female. These species then brood the young inside their mantle cavity, eventually releasing them into the water column as veliger larvae or as crawl-away juveniles.[35]
The bivalves are a highly successful class of invertebrates found in aquatic habitats throughout the world. Most are infaunal and live buried in sediment on the seabed, or in the sediment in freshwater habitats. A large number of bivalve species are found in the intertidal and sublittoral zones of the oceans. A sandy sea beach may superficially appear to be devoid of life, but there is often a very large number of bivalves and other invertebrates living beneath the surface of the sand. On a large beach in South Wales, careful sampling produced an estimate of 1.44 million cockles (Cerastoderma edule) per acre of beach.[50]
Bivalves inhabit the tropics as well as temperate and boreal waters. A number of species can survive and even flourish in extreme conditions. They are abundant in the Arctic, about 140 species being known from that zone.[51] The Antarctic scallop, Adamussium colbecki, lives under the sea ice at the other end of the globe, where the sub-zero temperatures mean that growth rates are very slow.[52] The giant mussel, Bathymodiolus thermophilus, and the giant white clam, Calyptogena magnifica, both live clustered around hydrothermal vents at abyssal depths in the Pacific Ocean. They havechemosymbiotic bacteria in their gills that oxidise hydrogen sulphide, and the molluscs absorb nutrients synthesized by these bacteria.[53] The saddle oyster, Enigmonia aenigmatica, is a marine species that could be considered amphibious. It lives above the high tide mark in the tropical Indo-Pacific on the underside of mangrove leaves, on mangrove branches and on sea walls in the splash zone.[54]
Most bivalves adopt a sedentary or even sessile life style, often spending their whole lives in the area in which they first settled as juveniles. The majority of bivalves are infaunal, living under the seabed, buried in soft substrates such as sand, silt, mud, gravel or coral fragments. Many of these live in the intertidal zone where the sediment remains damp even when the tide is out. When buried in the sediment, burrowing bivalves are protected from the pounding of waves, desiccation and overheating during low tide, and variations in salinity caused by rainwater. They are also out of the reach of many predators.[58] Their general strategy is to extend their siphons to the surface for feeding and respiration during high tide, but to descend to greater depths or keep their shell tightly shut when the tide goes out.[58] They use their muscular foot to dig into the substrate. Other bivalves, such as mussels, attach themselves to hard surfaces using tough byssus threads made of keratin and proteins. They are more exposed to attack by predators than the burrowing bivalves. Some bivalves, including the true oysters, the jewel boxes, the jingle shells, the thorny oysters and the kitten’s paws, cement themselves to stones, rock or larger dead shells.[61] In oysters the lower valve may be almost flat while the upper valve develops layer upon layer of thin horny material reinforced with calcium carbonate. Oysters sometimes occur in dense beds in the neritic zoneand, like most bivalves, are filter feeders.[16]
Razor shells can dig themselves into the sand with great speed to escape predation. When a Pacific razor clam (Siliqua patula) is laid on the surface of the beach it can bury itself completely in seven seconds [70] and the Atlantic jackknife clam, Ensis directus, can do the same within fifteen seconds.[71] Scallops and file clams can swim by opening and closing their valves rapidly; water is ejected on either side of the hinge area and they move with the flapping valves in front.[72] Scallops have simple eyes around the margin of the mantle and can clap their valves shut to move sharply, hinge first, to escape from danger.[72] Cockles can use their foot to move across the seabed or leap away from threats. The foot is first extended before being contracted suddenly when it acts like a spring, projecting the animal forwards.[73]
In many bivalves that have siphons, they can be retracted back into the safety of the shell. If the siphons inadvertently get attacked by a predator, they snap off. The animal can regenerate them later, a process that starts when the cells close to the damaged site become activated and remodel the tissue back to its pre-existing form and size.[74]
File shells such as Limaria fragilis can produce a noxious secretion when stressed. It has numerous tentacles which fringe its mantle and protrude some distance from the shell when it is feeding. If attacked, it sheds tentacles in a process known as autotomy. The toxin released by this is distasteful and the detached tentacles continue to writhe which may also serve to distract potential predators.[75]
Notes from Wikipedia. For more details: http://en.wikipedia.org/wiki/Bivalvia](http://24.media.tumblr.com/tumblr_mei95540Tk1rw22b7o1_500.jpg)
![Bivalvia, commonly referred to as bivalves, are the class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts. They include clams, oysters, mussels, scallops, and numerous other families. The majority are filter feeders and have no head orradula. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment on the seabed, where they are safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. A few bore into wood, clay or stone and live inside these substances. Some bivalves, such as the scallops, can swim.
The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. These are joined together along one edge by a flexible ligament that, in conjunction with interlocking “teeth” on each of the valves, forms the hinge. This arrangement allows the shell to be opened and closed without the two halves becoming disarticulated. The shell is typically bilaterally symmetrical, with the hinge lying in the sagittal plane. Adult shell sizes vary from fractions of a millimetre to over a metre in length, but the majority of species do not exceed 10 cm (4 in).
Bivalves vary greatly in overall shape. Some, such as the cockles, are nearly globular and can jump by bending and straightening the foot. Others, such as the razor clams, are burrowing specialists with elongated shells and powerful feet for digging. The shipworms of the family Teredinidae have greatly elongated bodies, but the shell valves are much reduced and restricted to the anterior end of the body, where they function as scraping organs that permit the animal to dig tunnels through wood.[9]
Near the hinge of the shell is the umbone or beak, a rounded, knobbly protuberance. This represents the oldest portion of the shell, with extra material later being laid down along the margins on the opposite side. The hinge area is the dorsal region of the shell and the lower margin is the ventral region. The anterior or front of the shell is where the byssus and foot are located, and the posterior of the shell is where the siphons are located. When the umbone is uppermost, the valve with the anterior end to the left is considered to be the left valve, while the valve with the anterior end to the right is the right valve.[10]
In all molluscs, the mantle forms a thin membrane covering the animal’s body and extending out from it in flaps or lobes. In bivalves, the mantle lobes secrete the valves, and the mantle crest secretes the whole hinge mechanism consisting of ligament, byssus threads, and teeth.[11]
Visible on the inside of most empty bivalve valves is a shiny line that runs parallel to the outer margin of the shell and often connects the two adductor muscle scars. This line (known as the pallial line) exists because parallel to the opening edge of the bivalve’s shell, the mantle is attached to the shell by a continuous narrow row of minute mantle retractor muscles. The function of these small muscles is to pull the loose edge of the mantle up out of harm’s way when this is necessary because of minor predation attempts. In many bivalves, the mantle edges fuse at the posterior end of the shell to form two siphons, through which water is inhaled and expelled for respiration and suspension feeding.[10] There is a pocket-like space into which the siphons fit when they are retracted. This is visible on the inside of the valve as an indentation on the pallial line which is known as the pallial sinus.[10]
The shell is composed of two calcareous valves held together by a ligament. The valves are made of either calcite, as is the case in oysters, or both calcite and aragonite. Sometimes the aragonite forms an inner, nacreous layer, as is the case in the order Pterioida. In other taxa, alternate layers of calcite and aragonite are laid down.[12] The ligament and byssus, if calcified, are composed of aragonite.[12] The outermost layer of the shell is theperiostracum, a skin-like layer which is composed of a horny organic substance. The periostracum is secreted in the groove between the outer and middle layers of the mantle, and is usually olive or brown in colour and easily abraded.[13] The outer surface of the valves is often sculpted with clams having fine concentric striations, scallops radial ribs and oysters a latticework of irregular markings.[14]
The shell is added to in two ways; the valves grow larger when more material is secreted by the mantle at the margin of the shell, and the valves themselves thicken gradually throughout the animal’s life as more calcareous matter is secreted by the mantle lobes. The two valves are held together at a hinge joint by a ligament composed of two keratinised proteins, tensilium and resilium. In different groups of bivalves the ligament can be internal or external in position. The main function of the ligament (as well as joining the valves together) is to passively cause the shell to open. The shell is actively closed using the adductor muscle or muscles attached to the inner surface of both valves. The position of the muscles is often clearly visible on the inside of empty valves as circular or oval muscle scars. Along the hinge line of the shell there are often a number of hinge teeth which prevent the valves from moving laterally relative to one another. The arrangement of these teeth is often important in identifying bivalves.[16]
The sensory organs of bivalves are not well developed and are largely located on the posterior mantle margins. The organs are usually mechanoreceptors or chemoreceptors located in shorttentacles. The chemoreceptor cells taste the water and are sensitive to touch. They are typically found near the siphons, but in some species may fringe the entire mantle cavity.[18] Theosphradium is a patch of sensory cells located below the posterior adductor muscle that may serve to taste the water or measure its turbidity, but is probably not homologous with the structure of the same name found in snails and slugs.[19] Statocysts within the organism help the bivalve to sense and correct its orientation. Each statocyst consists of a small sac lined with sensory cilia that detects the movement of a mineral mass, a statolith, under gravity.[20][21] In the order Anomalodesmata, the inhalant siphon is surrounded by vibration-sensitive tentacles for detecting prey.[22]
Many bivalves have no eyes, but a few members of Arcoidea, Limopsoidea, Mytiloidea, Anomioidea, Ostreoidea and Limoidea have simple eyes on the margin of the mantle. These consist of a pit of photo-sensory cells and a lens.[23] Scallops have more complex eyes with a lens, a two-layered retina and a concave mirror.[24] All bivalves have light-sensitive cells that can detect a shadow falling over the animal.[17]
The main muscular system in bivalves is the posterior and anterior adductor muscles, although the anterior muscles may be reduced or even lost in some species. These strong muscles connect the two valves and contract in order to close the shell. They work in opposition to the ligament which tends to pull the valves apart.[16] In sedentary or recumbent bivalves that lie on one valve, such as the oysters and scallops, the anterior adductor muscle has been lost and the posterior muscle is positioned centrally. In file shells that can swim by flapping their valves, there is also a single, central adductor muscle.[13] These muscles are composed of two types of muscle fibre, striated muscle bundles for fast actions and smooth muscle bundles for maintaining a steady pull.[13]
The mantle suspender muscles attach the mantle to the shell and leave an arc-shaped scar on the inside of the valve, the pallial line. The paired pedal protractor and retractor muscles operate the animal’s foot. Some bivalves, such as oysters and most scallops, are unable to extend their foot and in them, these muscles are absent. Other paired muscles control the siphons and the byssus.[10][13]
Most bivalves are filter feeders, using their gills to capture particulate food such as phytoplankton from the water. The Protobranchs feed in a different way, scraping detritus from the seabed, and this may be the original mode of feeding used by all bivalves before the gills became adapted for filter feeding. These primitive bivalves hold onto the substratum with a pair of tentacles at the edge of the mouth, each of which has a single palp, or flap. The tentacles are covered in mucus, which traps the food, and cilia, which transport the particles back to the palps. These then sort the particles, rejecting those that are unsuitable or too large to digest, and conveying others to the mouth.[20]
In the Filibranchia and Eulamellibranchia, water is drawn into the shell from the posterior ventral surface of the animal, passes upwards through the gills and doubles back to be expelled just above the intake. In burrowing species, there may be two elongated, retractable siphons reaching up to the seabed, one each for the inhalant and exhalant streams of water. The gills of filter-feeding bivalves are known as ctenidia and have become highly modified to increase their ability to capture food. For example, the cilia on the gills, which originally served to remove unwanted sediment, have become adapted to capture food particles, and transport them in a steady stream of mucus to the mouth. The filaments of the gills are also much longer than those in more primitive bivalves, and are folded over to create a groove through which food can be transported. The structure of the gills varies considerably, and can serve as a useful means for classifying bivalves into groups.[28]
A few bivalves, such as the granular poromya (Poromya granulata), are carnivorous, eating much larger prey than the tiny microalgae consumed by other bivalves. In these animals, the gills are relatively small, and form a perforated barrier separating the main mantle cavity from a smaller chamber through which the water is exhaled. Muscles draw water in through the inhalant siphon which is modified into a cowl-shaped organ, sucking in small crustaceans and worms at the same time. The siphon can be retracted quickly and inverted, bringing the prey within reach of the mouth. The gut is modified so that large food particles can be digested.[27]
The sexes are usually separate in bivalves but some hermaphroditism is known. The gonads are located close to the intestines, and either open into the nephridia, or through a separate pore into the mantle cavity.[33] The ripe gonads of male and females release sperm and eggs into the water column. Spawning may take place continually or be triggered by environmental factors such as day length, water temperature or the presence of sperm in the water. Some species are “dribble spawners” but others release their gametes in batches or all at once. Mass spawning events sometimes take place when all the bivalves in an area synchronise their release of spawn.[34]
Fertilization is usually external. Typically, there is a short stage lasting a few hours or days before the eggs hatch into trochophore larvae. These later develop into veliger larvae which settle on the seabed and undergo metamorphosis into juveniles known as spat.[33] In some species, such as those in the genus Lasaea, females draw water containing sperm in through their inhalant siphons and fertilisation is inside the female. These species then brood the young inside their mantle cavity, eventually releasing them into the water column as veliger larvae or as crawl-away juveniles.[35]
The bivalves are a highly successful class of invertebrates found in aquatic habitats throughout the world. Most are infaunal and live buried in sediment on the seabed, or in the sediment in freshwater habitats. A large number of bivalve species are found in the intertidal and sublittoral zones of the oceans. A sandy sea beach may superficially appear to be devoid of life, but there is often a very large number of bivalves and other invertebrates living beneath the surface of the sand. On a large beach in South Wales, careful sampling produced an estimate of 1.44 million cockles (Cerastoderma edule) per acre of beach.[50]
Bivalves inhabit the tropics as well as temperate and boreal waters. A number of species can survive and even flourish in extreme conditions. They are abundant in the Arctic, about 140 species being known from that zone.[51] The Antarctic scallop, Adamussium colbecki, lives under the sea ice at the other end of the globe, where the sub-zero temperatures mean that growth rates are very slow.[52] The giant mussel, Bathymodiolus thermophilus, and the giant white clam, Calyptogena magnifica, both live clustered around hydrothermal vents at abyssal depths in the Pacific Ocean. They havechemosymbiotic bacteria in their gills that oxidise hydrogen sulphide, and the molluscs absorb nutrients synthesized by these bacteria.[53] The saddle oyster, Enigmonia aenigmatica, is a marine species that could be considered amphibious. It lives above the high tide mark in the tropical Indo-Pacific on the underside of mangrove leaves, on mangrove branches and on sea walls in the splash zone.[54]
Most bivalves adopt a sedentary or even sessile life style, often spending their whole lives in the area in which they first settled as juveniles. The majority of bivalves are infaunal, living under the seabed, buried in soft substrates such as sand, silt, mud, gravel or coral fragments. Many of these live in the intertidal zone where the sediment remains damp even when the tide is out. When buried in the sediment, burrowing bivalves are protected from the pounding of waves, desiccation and overheating during low tide, and variations in salinity caused by rainwater. They are also out of the reach of many predators.[58] Their general strategy is to extend their siphons to the surface for feeding and respiration during high tide, but to descend to greater depths or keep their shell tightly shut when the tide goes out.[58] They use their muscular foot to dig into the substrate. Other bivalves, such as mussels, attach themselves to hard surfaces using tough byssus threads made of keratin and proteins. They are more exposed to attack by predators than the burrowing bivalves. Some bivalves, including the true oysters, the jewel boxes, the jingle shells, the thorny oysters and the kitten’s paws, cement themselves to stones, rock or larger dead shells.[61] In oysters the lower valve may be almost flat while the upper valve develops layer upon layer of thin horny material reinforced with calcium carbonate. Oysters sometimes occur in dense beds in the neritic zoneand, like most bivalves, are filter feeders.[16]
Razor shells can dig themselves into the sand with great speed to escape predation. When a Pacific razor clam (Siliqua patula) is laid on the surface of the beach it can bury itself completely in seven seconds [70] and the Atlantic jackknife clam, Ensis directus, can do the same within fifteen seconds.[71] Scallops and file clams can swim by opening and closing their valves rapidly; water is ejected on either side of the hinge area and they move with the flapping valves in front.[72] Scallops have simple eyes around the margin of the mantle and can clap their valves shut to move sharply, hinge first, to escape from danger.[72] Cockles can use their foot to move across the seabed or leap away from threats. The foot is first extended before being contracted suddenly when it acts like a spring, projecting the animal forwards.[73]
In many bivalves that have siphons, they can be retracted back into the safety of the shell. If the siphons inadvertently get attacked by a predator, they snap off. The animal can regenerate them later, a process that starts when the cells close to the damaged site become activated and remodel the tissue back to its pre-existing form and size.[74]
File shells such as Limaria fragilis can produce a noxious secretion when stressed. It has numerous tentacles which fringe its mantle and protrude some distance from the shell when it is feeding. If attacked, it sheds tentacles in a process known as autotomy. The toxin released by this is distasteful and the detached tentacles continue to writhe which may also serve to distract potential predators.[75]
Notes from Wikipedia. For more details: http://en.wikipedia.org/wiki/Bivalvia](http://24.media.tumblr.com/tumblr_mei95540Tk1rw22b7o2_500.jpg)
![The oceanic whitetip shark, Carcharhinus longimanus, or Carcharhinus maou is a large pelagic shark inhabiting tropical and warm temperate seas. Its stocky body is most notable for its long, white-tipped, rounded fins.
This aggressive but slow-moving fish dominates feeding frenzies, and is a danger to shipwreck or air crash survivors.[2] Recent studies show steeply declining populations because its large fins are highly valued as the chief ingredient of shark fin soup and, as with other shark species, the whitetip faces mounting fishing pressure throughout its range.
The oceanic whitetip is found globally in deep, open water, with a temperature greater than 18 °C (64 °F).[7] It prefers waters between 20 °C (68 °F)and 28 °C (82 °F) and tends to withdraw from areas when temperatures fall outside of this.[6] They were once extremely common and widely distributed, and still inhabit a wide band around the globe; however, recent studies suggest that their numbers have drastically declined.[3] An analysis of the US pelagic longline logbook data between 1992–2000 (covering the Northwest and Western Central Atlantic) estimated a decline of 70% over that period.[1]
They are found worldwide between 45° north and 43° south latitude.[4][7] In 2004, an oceanic whitetip was discovered dead on the west coast of Sweden—far beyond what was once considered the northern boundary of its range.[8]
The shark spends most of its time in the upper layer of the ocean—to a depth of 150 metres (490 ft)[7]—and prefers off-shore, deep-ocean areas. According to longline capture data, increasing distance from land correlates to a greater population of sharks.[5] Occasionally it is found close to land, in waters as shallow as 37 metres (120 ft), mainly around mid-ocean islands such as Hawaii, or in areas where the continental shelf is narrow and there is access to nearby deep water. It is typically solitary, though gatherings have been observed where food is plentiful.[6] Unlike many animals, it does not have a diurnal cycle, and is active both day and night.[5] Its swimming style is slow, with widely spread pectoral fins. Despite their habitual isolation from members of their own species, pilot fish, dolphinfish, and remora may accompany them.
C. longimanus’ most distinguishing characteristics are its long, wing-like pectoral and dorsal fins. The fins are significantly larger than most other shark species, and are conspicuously rounded. The shark’s nose is rounded and its eyes are circular, with nictitating membranes.[5]
C. longimanus has a ‘typical’, although somewhat flattened requiem shark body, often with a mildly humpbacked aspect. It is bronze, brown, bluish or grey dorsally (the colour varies by region), and white ventrally (although it may occasionally have a yellow tint). The Oceanic Whitetip Shark is a medium-sized requiem shark. The largest specimen ever caught measured 4 m (13 ft), an exceptionally large size considering few specimens are known to exceed a length of 3 m (9.8 ft). The maximum reported weight is 170 kg (370 lb). The female is typically larger than the male by 10 cm (3.9 in). Males attain sexual maturity at 1.7 to 1.9 m (5.6 to 6.2 ft) and females about 1.8 to 2 m (5.9 to 6.6 ft).[5][6] In the Gulf of Mexico in the 1950s, the mean weight of Oceanic Whitetip Sharks was 86.4 kg (190 lb). In the 1990s, the sharks of the species from the same area averaged only 56.1 kg (124 lb).[10]
The shark has several kinds of teeth—those in the mandible (lower jaw) have a thin serrated tip and are relatively small and triangular (somewhat fang-like). There are between 13 and 15 teeth on either side of the symphysis. The teeth in the upper jaw are triangular, but much larger and broader with entirely serrated edges—there are 14 or 15 along each side of the symphysis.[5] Thedenticles lie flat and typically have between five and seven ridges.
C. longimanus feeds mainly on pelagic cephalopods and bony fish.[7] However, its diet can be far more varied and less selective—it is known to eat threadfins, stingrays, sea turtles, birds,gastropods, crustaceans, and mammalian carrion. The bony fish it feeds on include lancetfish, oarfish, barracuda, jacks, dolphinfish, marlin, tuna, and mackerel. Its feeding methods include biting into groups of fish and swimming through schools of tuna with an open mouth. When feeding with other species, it becomes aggressive.
The oceanic whitetip is usually solitary and slow-moving, and tends to cruise near the top of the water column, covering vast stretches of empty water scanning for possible food sources.[5] C. longimanus are not fast swimmers, but they are capable of surprising bursts of speed. The oceanic whitetip is a competitive, opportunistic predator that exploits the resource at hand, rather than avoiding trouble in favour of a possibly easier future meal.[6]
There does not seem to be segregation by sex and size. Whitetips follow schools of tuna or squid, and trail groups of cetaceans such as dolphins andpilot whales, scavenging their prey. Their instinct to follow is so strongly imprinted, from countless millennia following baitfish migrations, that they accompany ocean-going ships. When whaling took place in warm waters, oceanic whitetips were often responsible for much of the damage to floating carcasses.
Mating season is in early summer in the northwest Atlantic Ocean and southwest Indian Ocean, although females captured in the Pacific have been found with embryos year round, suggesting a longer mating season there.[6] The shark is viviparous—embryos develop in utero and are fed by a placental sac. Its gestation period is one year. Litter sizes vary from one to 15 with the young born at a length of about 0.6 metres (24 in).[1] Sexual maturity is reached at close to 1.75 metres (69 in) for males and 2 metres (80 in) for females.[1]
Famed oceanographic researcher Jacques Cousteau described the oceanic whitetip as “the most dangerous of all sharks”.[14] Despite the greater notoriety of the great white shark and other sharks habitually found nearer the shore, the oceanic whitetip is suspected to be responsible for many fatal attacks on humans, as a result of predation on survivors of shipwrecks or downed aircraft.
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_me91a6wMAn1rw22b7o1_500.jpg)
![The oceanic whitetip shark, Carcharhinus longimanus, or Carcharhinus maou is a large pelagic shark inhabiting tropical and warm temperate seas. Its stocky body is most notable for its long, white-tipped, rounded fins.
This aggressive but slow-moving fish dominates feeding frenzies, and is a danger to shipwreck or air crash survivors.[2] Recent studies show steeply declining populations because its large fins are highly valued as the chief ingredient of shark fin soup and, as with other shark species, the whitetip faces mounting fishing pressure throughout its range.
The oceanic whitetip is found globally in deep, open water, with a temperature greater than 18 °C (64 °F).[7] It prefers waters between 20 °C (68 °F)and 28 °C (82 °F) and tends to withdraw from areas when temperatures fall outside of this.[6] They were once extremely common and widely distributed, and still inhabit a wide band around the globe; however, recent studies suggest that their numbers have drastically declined.[3] An analysis of the US pelagic longline logbook data between 1992–2000 (covering the Northwest and Western Central Atlantic) estimated a decline of 70% over that period.[1]
They are found worldwide between 45° north and 43° south latitude.[4][7] In 2004, an oceanic whitetip was discovered dead on the west coast of Sweden—far beyond what was once considered the northern boundary of its range.[8]
The shark spends most of its time in the upper layer of the ocean—to a depth of 150 metres (490 ft)[7]—and prefers off-shore, deep-ocean areas. According to longline capture data, increasing distance from land correlates to a greater population of sharks.[5] Occasionally it is found close to land, in waters as shallow as 37 metres (120 ft), mainly around mid-ocean islands such as Hawaii, or in areas where the continental shelf is narrow and there is access to nearby deep water. It is typically solitary, though gatherings have been observed where food is plentiful.[6] Unlike many animals, it does not have a diurnal cycle, and is active both day and night.[5] Its swimming style is slow, with widely spread pectoral fins. Despite their habitual isolation from members of their own species, pilot fish, dolphinfish, and remora may accompany them.
C. longimanus’ most distinguishing characteristics are its long, wing-like pectoral and dorsal fins. The fins are significantly larger than most other shark species, and are conspicuously rounded. The shark’s nose is rounded and its eyes are circular, with nictitating membranes.[5]
C. longimanus has a ‘typical’, although somewhat flattened requiem shark body, often with a mildly humpbacked aspect. It is bronze, brown, bluish or grey dorsally (the colour varies by region), and white ventrally (although it may occasionally have a yellow tint). The Oceanic Whitetip Shark is a medium-sized requiem shark. The largest specimen ever caught measured 4 m (13 ft), an exceptionally large size considering few specimens are known to exceed a length of 3 m (9.8 ft). The maximum reported weight is 170 kg (370 lb). The female is typically larger than the male by 10 cm (3.9 in). Males attain sexual maturity at 1.7 to 1.9 m (5.6 to 6.2 ft) and females about 1.8 to 2 m (5.9 to 6.6 ft).[5][6] In the Gulf of Mexico in the 1950s, the mean weight of Oceanic Whitetip Sharks was 86.4 kg (190 lb). In the 1990s, the sharks of the species from the same area averaged only 56.1 kg (124 lb).[10]
The shark has several kinds of teeth—those in the mandible (lower jaw) have a thin serrated tip and are relatively small and triangular (somewhat fang-like). There are between 13 and 15 teeth on either side of the symphysis. The teeth in the upper jaw are triangular, but much larger and broader with entirely serrated edges—there are 14 or 15 along each side of the symphysis.[5] Thedenticles lie flat and typically have between five and seven ridges.
C. longimanus feeds mainly on pelagic cephalopods and bony fish.[7] However, its diet can be far more varied and less selective—it is known to eat threadfins, stingrays, sea turtles, birds,gastropods, crustaceans, and mammalian carrion. The bony fish it feeds on include lancetfish, oarfish, barracuda, jacks, dolphinfish, marlin, tuna, and mackerel. Its feeding methods include biting into groups of fish and swimming through schools of tuna with an open mouth. When feeding with other species, it becomes aggressive.
The oceanic whitetip is usually solitary and slow-moving, and tends to cruise near the top of the water column, covering vast stretches of empty water scanning for possible food sources.[5] C. longimanus are not fast swimmers, but they are capable of surprising bursts of speed. The oceanic whitetip is a competitive, opportunistic predator that exploits the resource at hand, rather than avoiding trouble in favour of a possibly easier future meal.[6]
There does not seem to be segregation by sex and size. Whitetips follow schools of tuna or squid, and trail groups of cetaceans such as dolphins andpilot whales, scavenging their prey. Their instinct to follow is so strongly imprinted, from countless millennia following baitfish migrations, that they accompany ocean-going ships. When whaling took place in warm waters, oceanic whitetips were often responsible for much of the damage to floating carcasses.
Mating season is in early summer in the northwest Atlantic Ocean and southwest Indian Ocean, although females captured in the Pacific have been found with embryos year round, suggesting a longer mating season there.[6] The shark is viviparous—embryos develop in utero and are fed by a placental sac. Its gestation period is one year. Litter sizes vary from one to 15 with the young born at a length of about 0.6 metres (24 in).[1] Sexual maturity is reached at close to 1.75 metres (69 in) for males and 2 metres (80 in) for females.[1]
Famed oceanographic researcher Jacques Cousteau described the oceanic whitetip as “the most dangerous of all sharks”.[14] Despite the greater notoriety of the great white shark and other sharks habitually found nearer the shore, the oceanic whitetip is suspected to be responsible for many fatal attacks on humans, as a result of predation on survivors of shipwrecks or downed aircraft.
Notes from Wikipedia](http://24.media.tumblr.com/tumblr_me91a6wMAn1rw22b7o2_500.jpg)
![Cerianthus is a genus of tube-dwelling anemones in the family Cerianthidae.
Its typical shape makes it one of the most fascinating marine invertebrates.
Sciafila species (The sciafilia is the provision of certain bodies of both animals and plants living in the shadow), the tips of the tentacles are bioluminescent.
They are solitary corals that lives mainly on sandy and muddy in the tropical and sub-tropical countries around the world, including the Mediterranean Sea.
They are predators,scavengers and omnivores.[2]
Members of this genus do not have a pedal disc with which to hold themselves in position. Instead they live semi-buried in soft substrate surrounded by a parchment-like tube which they secrete. This surrounds the whole anemone up to its crown of tentacles. Sand grains, debris and shell fragments usually stick to the outer side of the tube. When it is disturbed, the anemone retracts swiftly back into the tube. Some of the larger species can have a column of up to 25 inches (640 mm) in length. The longitudinal muscles in the trunk are powerful but the transverse ones are weak. The outer ring of tentacles are long and tapering. The tube is flexible and the anemone can extend its tentacles a surprisingly long way. The inner ring of tentacles surrounds the central mouth and assists in pushing food inside.[2]
The tentacles are equipped with stinging cells (nematocysts) that are used to affect both predators and prey.
Notes from Wikipedia](http://24.media.tumblr.com/tumblr_mdvytndr7D1rw22b7o1_500.jpg)
![Cerianthus is a genus of tube-dwelling anemones in the family Cerianthidae.
Its typical shape makes it one of the most fascinating marine invertebrates.
Sciafila species (The sciafilia is the provision of certain bodies of both animals and plants living in the shadow), the tips of the tentacles are bioluminescent.
They are solitary corals that lives mainly on sandy and muddy in the tropical and sub-tropical countries around the world, including the Mediterranean Sea.
They are predators,scavengers and omnivores.[2]
Members of this genus do not have a pedal disc with which to hold themselves in position. Instead they live semi-buried in soft substrate surrounded by a parchment-like tube which they secrete. This surrounds the whole anemone up to its crown of tentacles. Sand grains, debris and shell fragments usually stick to the outer side of the tube. When it is disturbed, the anemone retracts swiftly back into the tube. Some of the larger species can have a column of up to 25 inches (640 mm) in length. The longitudinal muscles in the trunk are powerful but the transverse ones are weak. The outer ring of tentacles are long and tapering. The tube is flexible and the anemone can extend its tentacles a surprisingly long way. The inner ring of tentacles surrounds the central mouth and assists in pushing food inside.[2]
The tentacles are equipped with stinging cells (nematocysts) that are used to affect both predators and prey.
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_mdvytndr7D1rw22b7o2_500.jpg)
![Cerianthus is a genus of tube-dwelling anemones in the family Cerianthidae.
Its typical shape makes it one of the most fascinating marine invertebrates.
Sciafila species (The sciafilia is the provision of certain bodies of both animals and plants living in the shadow), the tips of the tentacles are bioluminescent.
They are solitary corals that lives mainly on sandy and muddy in the tropical and sub-tropical countries around the world, including the Mediterranean Sea.
They are predators,scavengers and omnivores.[2]
Members of this genus do not have a pedal disc with which to hold themselves in position. Instead they live semi-buried in soft substrate surrounded by a parchment-like tube which they secrete. This surrounds the whole anemone up to its crown of tentacles. Sand grains, debris and shell fragments usually stick to the outer side of the tube. When it is disturbed, the anemone retracts swiftly back into the tube. Some of the larger species can have a column of up to 25 inches (640 mm) in length. The longitudinal muscles in the trunk are powerful but the transverse ones are weak. The outer ring of tentacles are long and tapering. The tube is flexible and the anemone can extend its tentacles a surprisingly long way. The inner ring of tentacles surrounds the central mouth and assists in pushing food inside.[2]
The tentacles are equipped with stinging cells (nematocysts) that are used to affect both predators and prey.
Notes from Wikipedia](http://24.media.tumblr.com/tumblr_mdvytndr7D1rw22b7o3_500.jpg)
![The barracuda is a ray-finned fish known for its large size and fearsome appearance. Its body is long, fairly compressed, and covered with small, smooth scales. Some species can reach up to 1.8 m (5.9 ft) in length and 30 cm (12 in) in width.[2] The barracuda is a saltwater fish of the genusSphyraena, the only genus in the family Sphyraenidae, and is found in tropical and subtropical oceans worldwide.
Barracudas are elongated fish, pike-like in appearance, with prominent, sharp-edged, fang-like teeth, much like piranhas, of all of different sizes, set in sockets of their large jaws. They have large, pointed heads with an underbite in many species. Their gill covers have no spines and are covered with small scales. Their two dorsal fins are widely separated, with the anterior fin having five spines, and the posterior fin having one spine and 9 soft rays. The posterior dorsal fin is similar in size to the anal fin and is situated above it. The lateral line is prominent and extends straight from head to tail. The spinous dorsal fin is placed above the pelvic fins and is normally retracted in a groove. The caudal fin is moderately forked with its posterior edged double-curved and is set at the end of a stout peduncle. The pectoral fins are placed low on the sides. Its swim bladder is large.
In most cases, a barracuda is dark green, dark blue, or gray on its upper body, with silvery sides and a chalky-white belly. Coloration varies somewhat between species. For some species, irregular black spots or a row of darker cross-bars occur on each side. Their fins may be yellowish or dusky. Barracudas live primarily in oceans, but certain species, such as the great barracuda, live in brackish water.
Some species grow quite large, such as the European barracuda, barracouta, or spet (S. sphyraena), found in the Mediterranean Sea and eastern Atlantic; the great barracuda, picuda or becuna (S. picuda), ranging on the Atlantic coast of tropical America from North Carolina to Brazil and reaching Bermuda. Other barracuda species are found around the world. Examples are the California barracuda (S. argentea), found from Puget Sound southwards to Cabo San Lucas, the Indian barracuda (S. jello), and the black-finned or Commerson’s barracuda (S. commersoni), from the seas of India and the Malay Peninsula and Archipelago.
Barracudas are voracious, opportunistic predators, relying on surprise and short bursts of speed (up to 27 mph (43 km/h))[3] to overtake their prey.
Adults of most species are more or less solitary, while young and half-grown fish frequently congregate. Barracuda prey primarily on fish (which may include some as large as themselves). They kill and consume larger prey by tearing chunks of flesh.
Like sharks, some species of barracuda are reputed to be dangerous to swimmers. Barracudas are scavengers, and may mistake snorkellers for large predators, following them in hopes of eating the remains of their prey. Swimmers have been reported being bitten by barracuda, but such incidents are rare and possibly caused by poor visibility. Barracuda generally avoid muddy shallows, so attacks in surf are more likely to be by small sharks. Barracudas may mistake things that glint and shine for prey.[4] One incident reported a barracuda jumping out of water and injuring a kayaker,[5] but a marine biologist at the University of Florida said the type of wound appeared to have rather been caused by a houndfish.[6]
Hand feeding or touching large barracuda in general is to be avoided. Spearfishing around barracudas can also be dangerous, as they are quite capable of ripping a chunk from a wounded fish thrashing on a spear.
Diamond rings and other shiny objects have been known to catch their attention and resemble prey to them. Caution should be taken when swimming near mangrove coastlines by covering or removing such items.
Notes from Wikipedia](http://24.media.tumblr.com/tumblr_mdqpd6EzaH1rw22b7o1_500.jpg)
![The barracuda is a ray-finned fish known for its large size and fearsome appearance. Its body is long, fairly compressed, and covered with small, smooth scales. Some species can reach up to 1.8 m (5.9 ft) in length and 30 cm (12 in) in width.[2] The barracuda is a saltwater fish of the genusSphyraena, the only genus in the family Sphyraenidae, and is found in tropical and subtropical oceans worldwide.
Barracudas are elongated fish, pike-like in appearance, with prominent, sharp-edged, fang-like teeth, much like piranhas, of all of different sizes, set in sockets of their large jaws. They have large, pointed heads with an underbite in many species. Their gill covers have no spines and are covered with small scales. Their two dorsal fins are widely separated, with the anterior fin having five spines, and the posterior fin having one spine and 9 soft rays. The posterior dorsal fin is similar in size to the anal fin and is situated above it. The lateral line is prominent and extends straight from head to tail. The spinous dorsal fin is placed above the pelvic fins and is normally retracted in a groove. The caudal fin is moderately forked with its posterior edged double-curved and is set at the end of a stout peduncle. The pectoral fins are placed low on the sides. Its swim bladder is large.
In most cases, a barracuda is dark green, dark blue, or gray on its upper body, with silvery sides and a chalky-white belly. Coloration varies somewhat between species. For some species, irregular black spots or a row of darker cross-bars occur on each side. Their fins may be yellowish or dusky. Barracudas live primarily in oceans, but certain species, such as the great barracuda, live in brackish water.
Some species grow quite large, such as the European barracuda, barracouta, or spet (S. sphyraena), found in the Mediterranean Sea and eastern Atlantic; the great barracuda, picuda or becuna (S. picuda), ranging on the Atlantic coast of tropical America from North Carolina to Brazil and reaching Bermuda. Other barracuda species are found around the world. Examples are the California barracuda (S. argentea), found from Puget Sound southwards to Cabo San Lucas, the Indian barracuda (S. jello), and the black-finned or Commerson’s barracuda (S. commersoni), from the seas of India and the Malay Peninsula and Archipelago.
Barracudas are voracious, opportunistic predators, relying on surprise and short bursts of speed (up to 27 mph (43 km/h))[3] to overtake their prey.
Adults of most species are more or less solitary, while young and half-grown fish frequently congregate. Barracuda prey primarily on fish (which may include some as large as themselves). They kill and consume larger prey by tearing chunks of flesh.
Like sharks, some species of barracuda are reputed to be dangerous to swimmers. Barracudas are scavengers, and may mistake snorkellers for large predators, following them in hopes of eating the remains of their prey. Swimmers have been reported being bitten by barracuda, but such incidents are rare and possibly caused by poor visibility. Barracuda generally avoid muddy shallows, so attacks in surf are more likely to be by small sharks. Barracudas may mistake things that glint and shine for prey.[4] One incident reported a barracuda jumping out of water and injuring a kayaker,[5] but a marine biologist at the University of Florida said the type of wound appeared to have rather been caused by a houndfish.[6]
Hand feeding or touching large barracuda in general is to be avoided. Spearfishing around barracudas can also be dangerous, as they are quite capable of ripping a chunk from a wounded fish thrashing on a spear.
Diamond rings and other shiny objects have been known to catch their attention and resemble prey to them. Caution should be taken when swimming near mangrove coastlines by covering or removing such items.
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_mdqpd6EzaH1rw22b7o2_500.jpg)
![The barracuda is a ray-finned fish known for its large size and fearsome appearance. Its body is long, fairly compressed, and covered with small, smooth scales. Some species can reach up to 1.8 m (5.9 ft) in length and 30 cm (12 in) in width.[2] The barracuda is a saltwater fish of the genusSphyraena, the only genus in the family Sphyraenidae, and is found in tropical and subtropical oceans worldwide.
Barracudas are elongated fish, pike-like in appearance, with prominent, sharp-edged, fang-like teeth, much like piranhas, of all of different sizes, set in sockets of their large jaws. They have large, pointed heads with an underbite in many species. Their gill covers have no spines and are covered with small scales. Their two dorsal fins are widely separated, with the anterior fin having five spines, and the posterior fin having one spine and 9 soft rays. The posterior dorsal fin is similar in size to the anal fin and is situated above it. The lateral line is prominent and extends straight from head to tail. The spinous dorsal fin is placed above the pelvic fins and is normally retracted in a groove. The caudal fin is moderately forked with its posterior edged double-curved and is set at the end of a stout peduncle. The pectoral fins are placed low on the sides. Its swim bladder is large.
In most cases, a barracuda is dark green, dark blue, or gray on its upper body, with silvery sides and a chalky-white belly. Coloration varies somewhat between species. For some species, irregular black spots or a row of darker cross-bars occur on each side. Their fins may be yellowish or dusky. Barracudas live primarily in oceans, but certain species, such as the great barracuda, live in brackish water.
Some species grow quite large, such as the European barracuda, barracouta, or spet (S. sphyraena), found in the Mediterranean Sea and eastern Atlantic; the great barracuda, picuda or becuna (S. picuda), ranging on the Atlantic coast of tropical America from North Carolina to Brazil and reaching Bermuda. Other barracuda species are found around the world. Examples are the California barracuda (S. argentea), found from Puget Sound southwards to Cabo San Lucas, the Indian barracuda (S. jello), and the black-finned or Commerson’s barracuda (S. commersoni), from the seas of India and the Malay Peninsula and Archipelago.
Barracudas are voracious, opportunistic predators, relying on surprise and short bursts of speed (up to 27 mph (43 km/h))[3] to overtake their prey.
Adults of most species are more or less solitary, while young and half-grown fish frequently congregate. Barracuda prey primarily on fish (which may include some as large as themselves). They kill and consume larger prey by tearing chunks of flesh.
Like sharks, some species of barracuda are reputed to be dangerous to swimmers. Barracudas are scavengers, and may mistake snorkellers for large predators, following them in hopes of eating the remains of their prey. Swimmers have been reported being bitten by barracuda, but such incidents are rare and possibly caused by poor visibility. Barracuda generally avoid muddy shallows, so attacks in surf are more likely to be by small sharks. Barracudas may mistake things that glint and shine for prey.[4] One incident reported a barracuda jumping out of water and injuring a kayaker,[5] but a marine biologist at the University of Florida said the type of wound appeared to have rather been caused by a houndfish.[6]
Hand feeding or touching large barracuda in general is to be avoided. Spearfishing around barracudas can also be dangerous, as they are quite capable of ripping a chunk from a wounded fish thrashing on a spear.
Diamond rings and other shiny objects have been known to catch their attention and resemble prey to them. Caution should be taken when swimming near mangrove coastlines by covering or removing such items.
Notes from Wikipedia](http://25.media.tumblr.com/tumblr_mdqpd6EzaH1rw22b7o3_500.jpg)
![The genus Manta contains two species of manta rays: the Reef Manta Ray (Manta alfredi) and the Giant Oceanic Manta Ray (Manta birostris),[3] which are the largest species of the rays in the family Mobulidae, and the largest rays in the world. Oceanic mantas reach at least 7 metres (23 ft) in width and there are anecdotal reports of even larger specimens, while reef mantas reach about 5.5 metres (18 ft) in width.[4]
Manta rays are circumglobal and are typically found in tropical and subtropical waters, although oceanic manta rays can be found in temperate waters.[3] Oceanic mantas reside in deep water, pelagic zones, making periodic visits to cleaning stations at seamounts and coastal reefs. Minimal concrete information exists on oceanic manta movements, but they are generally believed to be more transient and migratory than the smaller reef mantas, which tend to be resident to shallower coastal habitats.[4][5]
Most sharks, rays and skates (Elasmobranchii) have small brain-to-body ratios, but the ratio is relatively high in manta rays and the closely related Mobula rays.[6]
Etymology
The term manta derives from the Spanish word manta, meaning cloak or blanket. This term originated from a type of trap traditionally used to catch rays that has a form resembling a blanket.[13]
Manta Rays have many common names including Atlantic manta, Pacific manta, devilfish, and just manta.
Description
Manta rays have a distinctive body shape with triangular ‘wings’ and paddle-like lobes extending in front of their mouths. The disc width can reach at least 7 m (23 ft) and there are even anecdotal reports of up to 9.1 m (30 ft).[5] The average weight is 1,300 kilograms (2,900 lb). They are generally dark on the upper surface, ranging from black to greyish-blue and brown, with pale undersides; individuals have a unique pattern of blotches and scars that can be used to identify them. The large, cavernous mouth is situated at the front of the body and contains 18 rows of teeth on the lower jaw.[14]
Anatomy
Some ancestral characteristics degenerated due to the feeding change. For example, all that remains of the teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. The number and size of their dermal denticles are also reduced. Manta rays have a much thicker mucus body coating than other rays. Their spiracles are small and non-functional, as all water is consumed orally. Mantas have a tail similar to stingrays, but they have lost their stinger and are harmless to divers.[15]
Ecology
Feeding
Manta rays are bottom feeders and filter feeders. Mantas feed on plankton, fish larvae and the like that they strain from the water passing through their mouths and out of their gills as they swim. They catch their prey on gill rakers, flat plates of russet-colored spongy tissue spanning spaces between the manta’s gill bars. An average-sized manta is estimated to consume 20–30 kilograms (44–66 lb) of plankton per day.
Individuals use several feeding strategies. Barrel rolling is technique performed by a single manta, vertically rolling themselves backwards sometimes for hours at a time. Others bottom feed along the seabed using their cephalic fins (fleshy projections on either side of the mouth) to scoop up plankton which has sunk to the sea floor. Feeding chains are also observed when a groups as large as 30 mantas, feeding together, line up in a chain head-to-tail. In the Maldives, where plankton concentrations are particularly high, hundreds of rays will assemble and form a feeding vortex called cyclone feeding. Mantas will swim around in tight formation causing a literal cyclone. This behavior only happens a dozen or so times a year and have only been observed at Hanifaru Bay in the Maldives.[3]
While feeding, whale sharks can often be seen swimming in the same area.[18]
Manta rays are often host to remoras (Remorina spp.), which attach to the underside of larger specimens and consume food that falls from the mouth.[14]
Predation
The manta’s main predators are large sharks and, in some circumstances, orcas.[19]](http://25.media.tumblr.com/tumblr_mdf62l7i9H1rw22b7o1_500.jpg)
![The genus Manta contains two species of manta rays: the Reef Manta Ray (Manta alfredi) and the Giant Oceanic Manta Ray (Manta birostris),[3] which are the largest species of the rays in the family Mobulidae, and the largest rays in the world. Oceanic mantas reach at least 7 metres (23 ft) in width and there are anecdotal reports of even larger specimens, while reef mantas reach about 5.5 metres (18 ft) in width.[4]
Manta rays are circumglobal and are typically found in tropical and subtropical waters, although oceanic manta rays can be found in temperate waters.[3] Oceanic mantas reside in deep water, pelagic zones, making periodic visits to cleaning stations at seamounts and coastal reefs. Minimal concrete information exists on oceanic manta movements, but they are generally believed to be more transient and migratory than the smaller reef mantas, which tend to be resident to shallower coastal habitats.[4][5]
Most sharks, rays and skates (Elasmobranchii) have small brain-to-body ratios, but the ratio is relatively high in manta rays and the closely related Mobula rays.[6]
Etymology
The term manta derives from the Spanish word manta, meaning cloak or blanket. This term originated from a type of trap traditionally used to catch rays that has a form resembling a blanket.[13]
Manta Rays have many common names including Atlantic manta, Pacific manta, devilfish, and just manta.
Description
Manta rays have a distinctive body shape with triangular ‘wings’ and paddle-like lobes extending in front of their mouths. The disc width can reach at least 7 m (23 ft) and there are even anecdotal reports of up to 9.1 m (30 ft).[5] The average weight is 1,300 kilograms (2,900 lb). They are generally dark on the upper surface, ranging from black to greyish-blue and brown, with pale undersides; individuals have a unique pattern of blotches and scars that can be used to identify them. The large, cavernous mouth is situated at the front of the body and contains 18 rows of teeth on the lower jaw.[14]
Anatomy
Some ancestral characteristics degenerated due to the feeding change. For example, all that remains of the teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. The number and size of their dermal denticles are also reduced. Manta rays have a much thicker mucus body coating than other rays. Their spiracles are small and non-functional, as all water is consumed orally. Mantas have a tail similar to stingrays, but they have lost their stinger and are harmless to divers.[15]
Ecology
Feeding
Manta rays are bottom feeders and filter feeders. Mantas feed on plankton, fish larvae and the like that they strain from the water passing through their mouths and out of their gills as they swim. They catch their prey on gill rakers, flat plates of russet-colored spongy tissue spanning spaces between the manta’s gill bars. An average-sized manta is estimated to consume 20–30 kilograms (44–66 lb) of plankton per day.
Individuals use several feeding strategies. Barrel rolling is technique performed by a single manta, vertically rolling themselves backwards sometimes for hours at a time. Others bottom feed along the seabed using their cephalic fins (fleshy projections on either side of the mouth) to scoop up plankton which has sunk to the sea floor. Feeding chains are also observed when a groups as large as 30 mantas, feeding together, line up in a chain head-to-tail. In the Maldives, where plankton concentrations are particularly high, hundreds of rays will assemble and form a feeding vortex called cyclone feeding. Mantas will swim around in tight formation causing a literal cyclone. This behavior only happens a dozen or so times a year and have only been observed at Hanifaru Bay in the Maldives.[3]
While feeding, whale sharks can often be seen swimming in the same area.[18]
Manta rays are often host to remoras (Remorina spp.), which attach to the underside of larger specimens and consume food that falls from the mouth.[14]
Predation
The manta’s main predators are large sharks and, in some circumstances, orcas.[19]](http://25.media.tumblr.com/tumblr_mdf62l7i9H1rw22b7o2_500.jpg)
![The genus Manta contains two species of manta rays: the Reef Manta Ray (Manta alfredi) and the Giant Oceanic Manta Ray (Manta birostris),[3] which are the largest species of the rays in the family Mobulidae, and the largest rays in the world. Oceanic mantas reach at least 7 metres (23 ft) in width and there are anecdotal reports of even larger specimens, while reef mantas reach about 5.5 metres (18 ft) in width.[4]
Manta rays are circumglobal and are typically found in tropical and subtropical waters, although oceanic manta rays can be found in temperate waters.[3] Oceanic mantas reside in deep water, pelagic zones, making periodic visits to cleaning stations at seamounts and coastal reefs. Minimal concrete information exists on oceanic manta movements, but they are generally believed to be more transient and migratory than the smaller reef mantas, which tend to be resident to shallower coastal habitats.[4][5]
Most sharks, rays and skates (Elasmobranchii) have small brain-to-body ratios, but the ratio is relatively high in manta rays and the closely related Mobula rays.[6]
Etymology
The term manta derives from the Spanish word manta, meaning cloak or blanket. This term originated from a type of trap traditionally used to catch rays that has a form resembling a blanket.[13]
Manta Rays have many common names including Atlantic manta, Pacific manta, devilfish, and just manta.
Description
Manta rays have a distinctive body shape with triangular ‘wings’ and paddle-like lobes extending in front of their mouths. The disc width can reach at least 7 m (23 ft) and there are even anecdotal reports of up to 9.1 m (30 ft).[5] The average weight is 1,300 kilograms (2,900 lb). They are generally dark on the upper surface, ranging from black to greyish-blue and brown, with pale undersides; individuals have a unique pattern of blotches and scars that can be used to identify them. The large, cavernous mouth is situated at the front of the body and contains 18 rows of teeth on the lower jaw.[14]
Anatomy
Some ancestral characteristics degenerated due to the feeding change. For example, all that remains of the teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. The number and size of their dermal denticles are also reduced. Manta rays have a much thicker mucus body coating than other rays. Their spiracles are small and non-functional, as all water is consumed orally. Mantas have a tail similar to stingrays, but they have lost their stinger and are harmless to divers.[15]
Ecology
Feeding
Manta rays are bottom feeders and filter feeders. Mantas feed on plankton, fish larvae and the like that they strain from the water passing through their mouths and out of their gills as they swim. They catch their prey on gill rakers, flat plates of russet-colored spongy tissue spanning spaces between the manta’s gill bars. An average-sized manta is estimated to consume 20–30 kilograms (44–66 lb) of plankton per day.
Individuals use several feeding strategies. Barrel rolling is technique performed by a single manta, vertically rolling themselves backwards sometimes for hours at a time. Others bottom feed along the seabed using their cephalic fins (fleshy projections on either side of the mouth) to scoop up plankton which has sunk to the sea floor. Feeding chains are also observed when a groups as large as 30 mantas, feeding together, line up in a chain head-to-tail. In the Maldives, where plankton concentrations are particularly high, hundreds of rays will assemble and form a feeding vortex called cyclone feeding. Mantas will swim around in tight formation causing a literal cyclone. This behavior only happens a dozen or so times a year and have only been observed at Hanifaru Bay in the Maldives.[3]
While feeding, whale sharks can often be seen swimming in the same area.[18]
Manta rays are often host to remoras (Remorina spp.), which attach to the underside of larger specimens and consume food that falls from the mouth.[14]
Predation
The manta’s main predators are large sharks and, in some circumstances, orcas.[19]](http://25.media.tumblr.com/tumblr_mdf62l7i9H1rw22b7o3_500.jpg)
![The genus Manta contains two species of manta rays: the Reef Manta Ray (Manta alfredi) and the Giant Oceanic Manta Ray (Manta birostris),[3] which are the largest species of the rays in the family Mobulidae, and the largest rays in the world. Oceanic mantas reach at least 7 metres (23 ft) in width and there are anecdotal reports of even larger specimens, while reef mantas reach about 5.5 metres (18 ft) in width.[4]
Manta rays are circumglobal and are typically found in tropical and subtropical waters, although oceanic manta rays can be found in temperate waters.[3] Oceanic mantas reside in deep water, pelagic zones, making periodic visits to cleaning stations at seamounts and coastal reefs. Minimal concrete information exists on oceanic manta movements, but they are generally believed to be more transient and migratory than the smaller reef mantas, which tend to be resident to shallower coastal habitats.[4][5]
Most sharks, rays and skates (Elasmobranchii) have small brain-to-body ratios, but the ratio is relatively high in manta rays and the closely related Mobula rays.[6]
Etymology
The term manta derives from the Spanish word manta, meaning cloak or blanket. This term originated from a type of trap traditionally used to catch rays that has a form resembling a blanket.[13]
Manta Rays have many common names including Atlantic manta, Pacific manta, devilfish, and just manta.
Description
Manta rays have a distinctive body shape with triangular ‘wings’ and paddle-like lobes extending in front of their mouths. The disc width can reach at least 7 m (23 ft) and there are even anecdotal reports of up to 9.1 m (30 ft).[5] The average weight is 1,300 kilograms (2,900 lb). They are generally dark on the upper surface, ranging from black to greyish-blue and brown, with pale undersides; individuals have a unique pattern of blotches and scars that can be used to identify them. The large, cavernous mouth is situated at the front of the body and contains 18 rows of teeth on the lower jaw.[14]
Anatomy
Some ancestral characteristics degenerated due to the feeding change. For example, all that remains of the teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. The number and size of their dermal denticles are also reduced. Manta rays have a much thicker mucus body coating than other rays. Their spiracles are small and non-functional, as all water is consumed orally. Mantas have a tail similar to stingrays, but they have lost their stinger and are harmless to divers.[15]
Ecology
Feeding
Manta rays are bottom feeders and filter feeders. Mantas feed on plankton, fish larvae and the like that they strain from the water passing through their mouths and out of their gills as they swim. They catch their prey on gill rakers, flat plates of russet-colored spongy tissue spanning spaces between the manta’s gill bars. An average-sized manta is estimated to consume 20–30 kilograms (44–66 lb) of plankton per day.
Individuals use several feeding strategies. Barrel rolling is technique performed by a single manta, vertically rolling themselves backwards sometimes for hours at a time. Others bottom feed along the seabed using their cephalic fins (fleshy projections on either side of the mouth) to scoop up plankton which has sunk to the sea floor. Feeding chains are also observed when a groups as large as 30 mantas, feeding together, line up in a chain head-to-tail. In the Maldives, where plankton concentrations are particularly high, hundreds of rays will assemble and form a feeding vortex called cyclone feeding. Mantas will swim around in tight formation causing a literal cyclone. This behavior only happens a dozen or so times a year and have only been observed at Hanifaru Bay in the Maldives.[3]
While feeding, whale sharks can often be seen swimming in the same area.[18]
Manta rays are often host to remoras (Remorina spp.), which attach to the underside of larger specimens and consume food that falls from the mouth.[14]
Predation
The manta’s main predators are large sharks and, in some circumstances, orcas.[19]](http://24.media.tumblr.com/tumblr_mdf62l7i9H1rw22b7o4_500.jpg)
![The genus Manta contains two species of manta rays: the Reef Manta Ray (Manta alfredi) and the Giant Oceanic Manta Ray (Manta birostris),[3] which are the largest species of the rays in the family Mobulidae, and the largest rays in the world. Oceanic mantas reach at least 7 metres (23 ft) in width and there are anecdotal reports of even larger specimens, while reef mantas reach about 5.5 metres (18 ft) in width.[4]
Manta rays are circumglobal and are typically found in tropical and subtropical waters, although oceanic manta rays can be found in temperate waters.[3] Oceanic mantas reside in deep water, pelagic zones, making periodic visits to cleaning stations at seamounts and coastal reefs. Minimal concrete information exists on oceanic manta movements, but they are generally believed to be more transient and migratory than the smaller reef mantas, which tend to be resident to shallower coastal habitats.[4][5]
Most sharks, rays and skates (Elasmobranchii) have small brain-to-body ratios, but the ratio is relatively high in manta rays and the closely related Mobula rays.[6]
Etymology
The term manta derives from the Spanish word manta, meaning cloak or blanket. This term originated from a type of trap traditionally used to catch rays that has a form resembling a blanket.[13]
Manta Rays have many common names including Atlantic manta, Pacific manta, devilfish, and just manta.
Description
Manta rays have a distinctive body shape with triangular ‘wings’ and paddle-like lobes extending in front of their mouths. The disc width can reach at least 7 m (23 ft) and there are even anecdotal reports of up to 9.1 m (30 ft).[5] The average weight is 1,300 kilograms (2,900 lb). They are generally dark on the upper surface, ranging from black to greyish-blue and brown, with pale undersides; individuals have a unique pattern of blotches and scars that can be used to identify them. The large, cavernous mouth is situated at the front of the body and contains 18 rows of teeth on the lower jaw.[14]
Anatomy
Some ancestral characteristics degenerated due to the feeding change. For example, all that remains of the teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. The number and size of their dermal denticles are also reduced. Manta rays have a much thicker mucus body coating than other rays. Their spiracles are small and non-functional, as all water is consumed orally. Mantas have a tail similar to stingrays, but they have lost their stinger and are harmless to divers.[15]
Ecology
Feeding
Manta rays are bottom feeders and filter feeders. Mantas feed on plankton, fish larvae and the like that they strain from the water passing through their mouths and out of their gills as they swim. They catch their prey on gill rakers, flat plates of russet-colored spongy tissue spanning spaces between the manta’s gill bars. An average-sized manta is estimated to consume 20–30 kilograms (44–66 lb) of plankton per day.
Individuals use several feeding strategies. Barrel rolling is technique performed by a single manta, vertically rolling themselves backwards sometimes for hours at a time. Others bottom feed along the seabed using their cephalic fins (fleshy projections on either side of the mouth) to scoop up plankton which has sunk to the sea floor. Feeding chains are also observed when a groups as large as 30 mantas, feeding together, line up in a chain head-to-tail. In the Maldives, where plankton concentrations are particularly high, hundreds of rays will assemble and form a feeding vortex called cyclone feeding. Mantas will swim around in tight formation causing a literal cyclone. This behavior only happens a dozen or so times a year and have only been observed at Hanifaru Bay in the Maldives.[3]
While feeding, whale sharks can often be seen swimming in the same area.[18]
Manta rays are often host to remoras (Remorina spp.), which attach to the underside of larger specimens and consume food that falls from the mouth.[14]
Predation
The manta’s main predators are large sharks and, in some circumstances, orcas.[19]](http://25.media.tumblr.com/tumblr_mdf62l7i9H1rw22b7o5_500.jpg)
