Juliidae, common name the bivalved gastropods, is a family of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an opisthobranch group. These are sacoglossan (sap-sucking) sea snails, and many of them are green in color. These snails are extremely unusual in that their shells consist of two separate hinged pieces or valves. The valves are joined by a ligament, and look nothing like a normal snail shell; instead the valves look almost exactly like the two hinged valves of a clam, a bivalve mollusk, a related but very different class of mollusks.