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A division of opisthobranchiate mollusks, having no shell except while very young. The gills are naked and situated upon the back or sides. See Ceratobranchia.

Any one of numerous species of freshwater pectinibranchiate mollusks, belonging to Paludina, Melantho, and allied genera. They have an operculated shell which is usually green, often with brown bands. See Illust. of Pond snail, under Pond.

An extensive division of pectinibranchiate gastropods, including those that have a long retractile proboscis, with the mouth at the end, as the cones, whelks, tritons, and cowries. See Illust. of Gastropoda, and of Winkle.

A division of opisthobranchiate mollusks having the branchiæ in a wreath or group around the anal opening, as in the genus Doris.

A division of pectinibranchiate gastropods, having the head prolonged into a snout which is not retractile.

Scutibranchiate. -- n.

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 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 dorsibranchiate annelid, belonging to Aphrodite and allied genera, having long, slender, hairlike setæ on the sides.

Any marine tectibranchiate gastropod of the genus Umbrella, having an umbrella-shaped shell; -- called also umbrella shell. Umbrella ant (Zoöl.), the sauba ant; -- so called because it carries bits of leaves over its back when foraging. Called also parasol ant. -- Umbrella bird (Zoöl.), a South American bird (Cephalop…