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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 terminology used to describe the shells of gastropods includes: Aperture: the opening of the shell; Lip: peristome: the margin of the aperture; Apex: the smallest few whorls of the shell; Body whorl (or last whorl): the largest whorl in which the main part of the visceral mass of the mollusk is found
This space contains the mollusk's gills, anus, osphradium, nephridiopores, and gonopores. The mantle cavity functions as a respiratory chamber in most mollusks. In bivalves it is usually part of the feeding structure. In some mollusks the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory ...
Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks [a] (/ ˈ m ɒ l ə s k s /). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda . [ 5 ]
The term seashell is also applied loosely to mollusk shells that are not of marine origin, for example by people walking the shores of lakes and rivers using the term for the freshwater mollusk shells they encounter. Seashells purchased from tourist shops or dealers may include various freshwater and terrestrial shells as well.
There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body. The skeleton of the fish is made of either cartilage (cartilaginous fishes) or bone (bony fishes).
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 ).