mollusk

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Conchyliologie Tableau de la Classification des Coquilles

Organizational levels and body diagrams of mollusks

blue-ringed octopus

Know about the two optical structures of blue-rayed limpet that give the blue-rayed limpet its unique and brilliant blue stripes

Tree of life illustrating the three-domain classification of life-forms

The structure of snail shells explained

Representative mollusks. Bivalves have a shell with two halves. Filter feeders, they take in food and water through a tubular siphon. In the clam, a muscular foot is used for burrowing and creeping. The chitons, typically found adhering to rocks and shells, have shells divided into eight overlapping plates. Tusk shells, or scaphopods, are burrowing mollusks with a shell open at both ends; with the larger end buried in the sand, they feed on microorganisms captured by the tentacles. The whelks, like most gastropods (univalves), have a single shell, which is usually coiled; when threatened, the body can be pulled into the shell, which is closed by a plate (operculum). Cephalopods have a well-developed head and a foot divided into numerous tentacles. The two long tentacles of the squid are used to capture prey, and the short arms transfer food to the mouth. The nautilus is the only cephalopod that has retained an exterior shell; by regulating the amount of gas and fluid in the interior chambers, it can regulate its buoyancy.

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mollusk summary

mollusk: Facts & Related Content

Written and fact-checked by The Information Architects of Encyclopaedia Britannica

Last Updated: Nov 03, 2025

Facts

Also Known As	Mollusca • mollusc

Photos and Videos

Conchyliologie Tableau de la Classification des Coquilles

Organizational levels and body diagrams of mollusks

blue-ringed octopus

Tree of life illustrating the three-domain classification of life-forms

Representative mollusks. Bivalves have a shell with two halves. Filter feeders, they take in food and water through a tubular siphon. In the clam, a muscular foot is used for burrowing and creeping. The chitons, typically found adhering to rocks and shells, have shells divided into eight overlapping plates. Tusk shells, or scaphopods, are burrowing mollusks with a shell open at both ends; with the larger end buried in the sand, they feed on microorganisms captured by the tentacles. The whelks, like most gastropods (univalves), have a single shell, which is usually coiled; when threatened, the body can be pulled into the shell, which is closed by a plate (operculum). Cephalopods have a well-developed head and a foot divided into numerous tentacles. The two long tentacles of the squid are used to capture prey, and the short arms transfer food to the mouth. The nautilus is the only cephalopod that has retained an exterior shell; by regulating the amount of gas and fluid in the interior chambers, it can regulate its buoyancy.

Know about the two optical structures of blue-rayed limpet that give the blue-rayed limpet its unique and brilliant blue stripes

The structure of snail shells explained

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Topics

gastropod bivalve Loboconcha Aculifera Visceroconcha Aplacophora cephalopod chiton nephridium monoplacophoran reptile fish insect bird mammal annelid echinoderm crustacean amphibian flatworm

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William Brooks

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