Your pet snail, Sammy, is one example of a mollusk, or a soft, spineless animal. In Sammy's case, he has a shell, though some mollusks don't.

It's a bit ironic that this term for a large phylum of invertebrates comes from a Latin word that means "soft," mollis, since many mollusks (or molluscs in Britspeak) have hard shells. The epithet comes from the nature of the creatures' bodies, whether in shell (like a snail) or without (like a slug).

Definitions of mollusk
  1. noun
    invertebrate having a soft unsegmented body usually enclosed in a shell
    synonyms: mollusc, shellfish
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    burrowing marine mollusk
    gastropod, univalve
    a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes
    chiton, coat-of-mail shell, polyplacophore, sea cradle
    primitive elongated bilaterally symmetrical marine mollusk having a mantle covered with eight calcareous plates
    bivalve, lamellibranch, pelecypod
    marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together
    cephalopod, cephalopod mollusk
    marine mollusk characterized by well-developed head and eyes and sucker-bearing tentacles
    tooth shell, tusk shell
    any of various seashore mollusks having a tapering tubular shell open at each end and a foot pointed like a spade for burrowing
    abalone, ear-shell
    any of various large edible marine gastropods of the genus Haliotis having an ear-shaped shell with pearly interior
    any of various edible tropical marine gastropods of the genus Strombus having a brightly-colored spiral shell with large outer lip
    freshwater or marine or terrestrial gastropod mollusk usually having an external enclosing spiral shell
    any of various terrestrial gastropods having an elongated slimy body and no external shell
    any of several creeping marine gastropods with a spirally coiled shell: whelks; tritons; moon shells; neritids
    Ancylus fluviatilis, freshwater limpet, river limpet
    minute conical gastropod superficially resembling a limpet but living and feeding on freshwater plants
    nudibranch, sea slug
    any of various marine gastropods of the suborder Nudibranchia having a shell-less and often beautifully colored body
    Aplysia punctata, sea hare
    naked marine gastropod having a soft body with reduced internal shell and two pairs of ear-like tentacles
    bubble shell
    marine gastropod mollusk having a very small thin shell
    any member of the genus Physa
    cowrie, cowry
    any of numerous tropical marine gastropods of the genus Cypraea having highly polished usually brightly marked shells
    aplacophoran, solenogaster
    deep-water wormlike mollusks lacking calcareous plates on the body but having fine slimy spicules on the covering mantle
    burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness
    common edible, burrowing European bivalve mollusk that has a strong, rounded shell with radiating ribs
    marine mollusks having a rough irregular shell; found on the sea bed mostly in coastal waters
    ark shell
    marine bivalve mollusk having a heavy toothed shell with a deep boat-like inner surface
    blood clam
    red-blooded clam
    marine or freshwater bivalve mollusk that lives attached to rocks etc.
    escallop, scallop, scollop
    edible marine bivalve having a fluted fan-shaped shell that swim by expelling water from the shell in a series of snapping motions
    marine bivalve that bores into rock or clay or wood by means of saw-like shells
    chambered nautilus, nautilus, pearly nautilus
    cephalopod of the Indian and Pacific oceans having a spiral shell with pale pearly partitions
    dibranch, dibranchiate, dibranchiate mollusk
    cephalopods having two gills
    a cephalopod with eight arms but lacking an internal shell
    cephalopods having eight short tentacles plus two long ones
    type of:
    any animal lacking a backbone or notochord; the term is not used as a scientific classification
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