protostome(redirected from Protosome)
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The opening into the archenteron formed by invagination of the blastula to form a gastrula.
[blasto- + G. poros, opening]
Any of numerous invertebrate animals of the group Protostomia, in which the mouth develops from the first opening in the embryo and the anus develops later, and including the mollusks, annelids, and arthropods.