'Univalve' definitions:

Definition of 'univalve'

adjective

Used of mollusks, especially gastropods, as snails etc. [ant: bivalve, bivalved]

noun

A class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes [syn: gastropod, univalve]

From: GCIDE

Univalve \U"ni*valve\, n. [Uni- + valve: cf. F. univalve.] (Zool.) A shell consisting of one valve only; a mollusk whose shell is composed of a single piece, as the snails and conchs. [1913 Webster]
Note: Most univalves are spiral and are the shells of gastropods, but many belong to cephalopods and pteropods. A large number of univalves belonging to the gastropods are conical, cup-shaped, or shieldlike, as the limpets. [1913 Webster] Univalve

From: GCIDE

Univalve \U"ni*valve\, Univalved \U"ni*valved\, a. [Cf. F. univalve.] (Bot. & Zool.) Having one valve; as, a univalve shell or pericarp. [1913 Webster]