n.
Pronunciation: ' pr ō -t ə - ˌ st ō m
Function: noun
Etymology: New Latin Protostomia, from prot- + Greek stoma mouth ― more at STOMACH
Date: 1959
: 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