noun pro·to·stome \ˈprō-tə-ˌstōm\

Definition of PROTOSTOME

:  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


New Latin Protostomia, from prot- + Greek stoma mouth — more at stomach
First Known Use: 1959


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