Zyg`o*bran"chi*a\, n. pl. [NL., from Gr. ? a yoke + ? a gill.] (Zo["o]l.) A division of marine gastropods in which the gills are developed on both sides of the body and the renal organs are also paired. The abalone (Haliotis
) and the keyhole limpet (Fissurella
) are examples.