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An extinct order or suborder of bivalve mollusks characteristic of the Cretaceous period; -- called also Rudista. See Illust. under Hippurite.

Boring, or hollowing out, rocks; -- said of certain mollusks which live in holes which they burrow in rocks. See Illust. of Lithodomus.

Any one of numerous species of marine bivalve mollusks of the genus Pecten and allied genera of the family Pectinidæ. The shell is usually radially ribbed, and the edge is therefore often undulated in a characteristic manner. The large adductor muscle of some the species is much used as food. One species (Vola Jacobæus…

A genus of oceanic nudibranchiate mollusks having the small branched gills situated on the upper side of four fleshy lateral lobes, and on the median caudal crest.

Any one of the large bivalve mollusks found on the open seacoast, especially those of the family Mactridæ, as the common American species. (Mactra, or Spisula, solidissima); -- called also beach clam, and surf clam.

f numerous species of ducks which frequent the seacoasts and feed mainly on fishes and mollusks. The scoters, eiders, old squaw, and ruddy duck are examples. They may be distinguished by the lobate hind toe.

Any tectibranchiate mollusk of the genus Aplysia. See Aplysia.

Any one of several species of nudibranchiate mollusks of the genus Doris and allied genera, having a smooth, thick, convex yellow body.

A nudibranch mollusk.

The shell of any marine mollusk.

e place, especially when firmly attached to some object; as, the oyster is a sedentary mollusk; the barnacles are sedentary crustaceans. Sedentary spider (Zoöl.), one of a tribe of spiders which rest motionless until their prey is caught in their web.

One of the transverse partitions dividing the shell of a mollusk, or of a rhizopod, into several chambers. See Illust. under Nautilus.

The hard calcareous or chitinous external covering of mollusks, crustaceans, and some other invertebrates. In some mollusks, as the cuttlefishes, it is internal, or concealed by the mantle. Also, the hard covering of some vertebrates, as the armadillo, the tortoise, and the like.

ernal covering consists of a shell, either testaceous, as in oysters, clams, and other mollusks, or crustaceous, as in lobsters and crabs.

Any long, slender, worm-shaped bivalve mollusk of Teredo and allied genera. The shipworms burrow in wood, and are destructive to wooden ships, piles of wharves, etc. See Teredo.

One of the tubes or folds of the mantle border of a bivalve or gastropod mollusk by which water is conducted into the gill cavity. See Illust. under Mya, and Lamellibranchiata.

A tribe of bivalve mollusks in which the posterior mantle border is prolonged into two tubes or siphons. Called also Siphoniata. See Siphon, 2 (a), and Quahaug.

Any one of numerous species of terrestrial pulmonate mollusks belonging to Limax and several related genera, in which the shell is either small and concealed in the mantle, or altogether wanting. They are closely allied to the land snails.

ond snail, etc. See under Ear, Edible, etc. -- Snail borer (Zoöl.), a boring univalve mollusk; a drill. -- Snail clover (Bot.), a cloverlike plant (Medicago scuttellata, also, M. Helix); -- so named from its pods, which resemble the shells of snails; -- called also snail trefoil, snail medic, and beehive. -- Snail f…

Any marine bivalve mollusk belonging to Solen or allied genera of the family Solenidæ; a razor shell.