Having one valve only, as a mollusk; not bivalve or multivalve; univalved or univalvular. See II.Having the carapace single, or not hinged in the middle line: specifying the cladocerous or daphniaceous crustaceans. [Now rare.] In botany, consisting of one valve or piece.n. In conchology, a univalve mollusk or its shell; a shell consisting of a single piece; formerly, a member of one of three Linnean divisions of Testacea, as distinguished from bivalves and multivalves.n. body-whorl or aperture are collectively the spire, ending at the tip, point, or apex. The opposite end of the shell is the base, which often presents a depression, the umbilicus; the circumference, a completely lipped aperture, is the peristome. The spiral line between the successive whorls or volutions is the suture. See words italicized above with various cuts there, or there cited.