Definitions for "Protostome"
One of the major lineages of animal evolution. Characterized by spiral, determinate cleavage of the egg, and by schizocoelous development. (Compare with deuterostome.)
the developmental pattern of animal blastula whereby the blastopore ultimately develops into the mouth, cleavage is typically spiral, and the coelom forms from by splitting.. This pattern is typical of many invertebrate groups (the "Protostomia"), including acoelomate, pseudocoelomate, and coelomate animals. These groups include flatworms, rotifers, nematodes, arthropods, molluscs, annelids, and many others.
Protostomes (from the Greek: first the mouth) are a taxon of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development.