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

First Known Use of protostome

1959, in the meaning defined above

History and Etymology for protostome

New Latin Protostomia, from prot- + Greek stoma mouth — more at stomach

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The first known use of protostome was in 1959

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