mollusk n.

"division of invertebrate animals with soft, unsegmented bodies, no jointed legs, and commonly covered by hard shells," 1797, from Modern Latin mollusca, chosen by Linnaeus as the name of an invertebrate order (1758), from neuter plural of Latin molluscus "thin-shelled," from mollis "soft" (from PIE root *mel- (1) "soft"). Linnæus applied the word to a heterogeneous group of invertebrates, not originally including mollusks with shells; the modern scientific use is after a classification proposed 1790s by French naturalist Georges Léopole Chrétien Frédéric Dagobert, Baron Cuvier (1769-1832).

Proto-Indo-European root meaning "soft," with derivatives referring to soft or softened materials.

It forms all or part of: amblyopia; bland; blandish; blenny; emollient; enamel; malacia; malaxation; malt; melt; mild; Mildred; milt; moil; mollify; Mollusca; mollusk; mulch; mullein; mutton; schmaltz; smelt (v.); smelt (n.).

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit mrdh "to neglect," also "to be moist;" Greek malakos "soft," malthon "weakling;" Latin mollire "soften," mollis "soft;" Old Irish meldach "tender."

see mollusk.