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The mollusc (or mollusk [a]) shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.
In addition, the water flows through incurrent siphon ventrally and exit out of the body through excurrent dorsally to the body. The valves of the shell are made of either calcite (as with, e.g. oysters) or both calcite and aragonite , usually with the aragonite forming an inner layer, as is the case with the Pteriida which have this layer in ...
The taxonomic term Bivalvia was first used by Linnaeus in the 10th edition of his Systema Naturae in 1758 to refer to animals having shells composed of two valves. [3] More recently, the class was known as Pelecypoda, meaning "axe-foot" (based on the shape of the foot of the animal when extended).
The less major anterior and posterior retractor muscles extend from the shell and attach the body to a structure called the foot. [4] This muscular foot is typical of most bivalves, extending anteriorly between the valves (via an anterior protractor muscle) and aiding in locomotion , burrowing and anchorage ( holdfast ).
Mussel (/ ˈ m ʌ s ə l /) is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.
For example, bluefin tuna maintain a core body temperature of 25–33 °C (77–91 °F), in water as cold as 6 °C (43 °F). However, unlike typical endothermic creatures such as mammals and birds, tuna do not maintain temperature within a relatively narrow range. [ 40 ]
Osmoregulation, or the maintenance of constant salinity within body tissue and fluids, is another challenge faced by freshwater Mollusca. Dillon (2000) [ 2 ] indicates that they have characteristically low tissue salinities relative to other freshwater animals, and unionid mussels have some of the lowest tissue salinities of any animal.
The optimum temperature for metabolism and oxygen consumption is between 18 and 24 °C (64 and 75 °F). [41] Variations in temperature can also induce a change in hemolymph protein levels along oxygen consumption. [41] As temperature increases, protein concentrations increase in order to accommodate the temperature.