PROTOSTOME

[pro.to.stome] n [NL Protostomia, fr. prot- + Gk stoma mouth--more at stomach] (ca. 1961): any of a major group (Protostomia) of bilateral metazoan animals (as mollusks, annelids, and arthropods) characterized in typical forms by determinate and spiral cleavage, formation of a mouth and anus directly from the blastopore, and formation of the coelom by splitting of the embryonic mesoderm--compare deuterostome