branchial cleft(n = noun.animal) gill cleft, gill slit - one of a series of slit openings in the pharynxes of fishes and aquatic amphibians through which water passes;
is a kind of anatomical structure, bodily structure, body structure, complex body part, structure

branchial, branchial arch, cleft, cleft foot, cleft lip, cleft palate, gill cleft, pudendal cleft, urogenital cleft