protostome

noun

pro·​to·​stome ˈprō-tə-ˌstōm 

: 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

Word History

Etymology

New Latin Protostomia, from prot- + Greek stoma mouth — more at stomach entry 1

First Known Use

1959, in the meaning defined above