Noun
protostome (plural protostomes)
Any animal, of the taxon Protostomia, in which the mouth is derived from the embryonic blastopore
If chaetognaths branched off from the protostomes before they evolved their distinctive protostome embryonic characters, they may have retained deuterostome characters inherited from early bilaterian ancestors. Source: Internet
The traditional view was that lophophorates were a mix of protostome and deuterostome features. Source: Internet