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Key People:William Keith BrooksAugustus A. Gould...(Show more)Related Topics:gastropodbivalvecephalopodchitonnephridium...(Show more)

mollusk, additionally spelled mollusc, any soft-bodied invertebrate the the phylum Mollusca, commonly wholly or partly enclosed in a calcium carbonate covering secreted through a soft mantle covering the body. Along with the insects and vertebrates, it is just one of the most varied groups in the pet kingdom, with almost 100,000 (possibly as many as 150,000) explained species. Every group contains an ecologically and also structurally immense selection of forms: the shell-less Caudofoveata; the narrow-footed gliders (Solenogastres); the serially valved chitons (Placophora or Polyplacophora); the cap-shaped neopilinids (Monoplacophora); the limpets, snails, and also slugs (Gastropoda); the clams, mussels, scallops, oysters, shipworms, and also cockles (Bivalvia); the tubiform come barrel-shaped tusk shells (Scaphopoda); and also the nautiluses, cuttlefishes, squids, and octopuses (Cephalopoda).

General features

Size variety and diversity the structure

Typical molluscan attributes have been substantially altered, or also lost, in countless subgroups. Amongst the cephalopods the giant squids (Architeuthis), the biggest living invertebrates, obtain a body length of eight metres (more 보다 26 feet); with the tentacle arms extended, the total length reaches come 22 metres. Other cephalopods exceed a size of one metre. Many of the remaining molluscan classes display a big variation in size: among bivalves the giant clam (Tridacna) varieties up come 135 centimetres (four feet) and also the pen covering (Pinna) indigenous 40 come 80 centimetres; amongst gastropods the sea hares (Aplysia) thrive from 40 come 100 centimetres and the Australian trumpet, or baler (Syrinx), up to 60 centimetres; amongst placophores the gumshoe, or gumboot chiton (Cryptochiton), achieves a length up to 30 come 43 centimetres; and, amongst solenogasters, Epimenia will a length of 15 to 30 centimetres. Finally, gastropods of the family members Entoconchidae, which room parasitic in echinoderm sea cucumbers, might reach a size of nearly 1.3 metres. In contrast, there are additionally minute members, less than one millimetre (0.04 inch) in size, amongst the solenogasters and gastropods.


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Are snails gastropods? space clams bivalves? learn the answers to these questions and more by acquisition this mollusk quiz.

Distribution and abundance

The mollusks have adapted to all habitats except air. Although usually marine, bivalves and also gastropods encompass freshwater species. Gastropods have also adapted to land, with thousands of species living a fully terrestrial existence. Discovered on rocky, sandy, and also muddy substrata, mollusks burrow, crawl, come to be cemented come the surface, or are free-swimming.

Mollusks are found worldwide, yet there is a preponderance that some teams in details areas of the world. The close combination of countless molluscan groups with your food source—whether by direct dependence ~ above a particular food supply (e.g., plant-eating, or herbivores) or by involvement in food chains—limits their geographic distribution; because that example, bivalves of the family members Teredinidae (shipworms) are associated with wood. In general, cold-water regions support fewer species.


Importance come humans

Mollusks space of basic importance within food chains and also as members that ecosystems. Certain types are of straight or indirect commercial and also even medical importance to humans. Plenty of gastropod species, because that example, are essential intermediate master for parasitic flatworms (class Trematoda, phylum Platyhelminthes), such together the species that reason schistosomiasis in humans. Most bivalves add to the organic turnover in the intertidal (littoral) zones of marine and also fresh water because, as filter feeders, they filter as much as 40 litres (10 gallons) that water per hour. This filtering activity, however, may likewise seriously interfere through the various populations the invertebrate larvae (plankton) discovered suspended and free-swimming in the water. One species, the zebra mussel (Dreissena polymorpha), is regarded as a specifically harmful exotic invader. Brought from Europe in ship ballast water, zebra mussels were required to the great Lakes in 1986. To date, they have caused countless dollars in commercial damages by clogging the water tube of power plants and cooling systems. They are driving numerous native freshwater bivalve species to extinction.

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Many gastropods, bivalves, and cephalopods are a source of food for countless cultures and also therefore play critical role in the fishing industries of many countries. Plenty of shell-bearing molluscan types are additionally used to fabricate ornaments and are harvested because that the pearl and mother-of-pearl industries.