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A large and diverse phylum of soft-bodied, usually unsegmented, coelomate animals , many of which live enclosed in a hard shell. They include the classes Gastropoda (winkles, whelks, slugs, snails, sea slugs etc.), Bivalvia (clams, cockles etc.), and other small classes of shells and the Cephalopoda (nautilus, squids and octopuses). The coelom* is small and the main body cavity is a blood-filled haemocoel. Molluscs have well-developed sense organs and nervous system, a heart and blood system.

Soft-bodied animals that usually produce an exoskeleton composed of calcium carbonate. This shell serves both protective and supportive purposes. All molluscs have a fleshy mantle -- a fold or lobe (or a pair of them) of fleshy material, which secretes, modifies and lines the shell.

Members of all classes except the bivalves possess a ribbon-like set of hooked teeth called radula. These they rasp (think of a fingernail file) back and forth over their food; vegetarian species use them to scrape algae off rocks and other substrates, while most molluscan carnivores use them to penetrate the surface of their prey.


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The Phylum Mollusca is a member of the Superphylum Eutrochozoa. Here is the complete "parentage" of Mollusca:

The Phylum Mollusca is further organized into finer groupings including:


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Bivalvia (common name bivalves) is a taxonomic class of marine and freshwater molluscs that have a shell in two hinged parts. This class includes clams, oysters, mussels, scallops, and many other families. The name Bivalvia was first used by Linnaeus in 1758, describing the shell, which is composed of two valves. More recently the class was known for a time as Pelecypoda, meaning "axe-foot" based on the soft parts of the animal. Other names which have been used for this class include Lamellibranchia (based on the plate-like gill elements, see ctenidium), Acephala (these animals have no head), and Bivalva (two valves). [more]


A cephalopod is any member of the molluscan class Cephalopoda (Greek plural (kephal?poda); "head-feet"). These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology. [more]




The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large. There are huge numbers of sea snails and sea slugs, as well as freshwater snails and freshwater limpets, and land snails and land slugs. [more]


Helcionelloida is the name given to an extinct group of ancient molluscs (phylum Mollusca). These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991. [more]


Monoplacophora, meaning "bearing one plate", is a polyphyletic class of mollusks with a cap-like shell, living on the bottom of deep sea. Extant representatives were unknown until 1952; previously they were known only from the fossil record. [more]


Chitons () are small to large, marine molluscs in the class Polyplacophora, which formerly was known as Amphineura. There are approximately 940 extant and 430 fossil species recognized. [more]




The tusk shells or scaphopods are a class of shelled marine mollusks. The scientific name of this class is Scaphopoda, meaning "shovel-footed". Shells of species within this class range from about 0.5 to 15 cm in length. Members of the Order Dentaliida are generally significantly larger than those of the Order Gadilida. [more]


Stenothecidae is an extinct family of univalved Cambrian molluscs. (Do not confuse with Cambrian problematic invertebrates with bivalved (dorsal and ventral) shell, members of the class Stenothecoida). [more]



At least 15 species and subspecies belong to the Class Tergomya.

More info about the Class Tergomya may be found here.


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Last Revised: August 22, 2014
2014/08/22 05:21:46