protostome
noun
pro·to·stome
| \ ˈprō-tə-ˌstōm
\
\
Definition of protostome
: any of a major group (Protostomia) of bilateral metazoan animals (such 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
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