LAMP SHELL

also called Brachiopod, any member of the phylum Brachiopoda, a group of bottom-dwelling marine invertebrates that superficially resemble bivalve mollusks. The shells of brachiopods are fundamentally dissimilar from those of the mollusks, as the valves of the shell enclose the body dorsally and ventrally, rather than laterally as in mollusks. The lower valve is often larger than the upper one, with an upturned beak' and rounded aperture near the hingea shape reminiscent of a Roman lamp, from which the name lamp shell is derived. Internally brachiopods differ from bivalve mollusks even more markedly. The body of the brachiopod is surprisingly small, measuring only about 5 to 100 millimetres (0.2 to 4 inches). A few brachiopods occur in deep water, but most are confined to shallow continental-shelf habitats. They are typically attached to solid surfaces either by a stalk or by direct cementation of the ventral valve.