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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.

[From New Latin Prōtostomia, taxon name : proto- + New Latin stoma; see stoma.]


(Zoology) a mollusc, annelid, arthropod or other animal in which the mouth develops before the anus at embryonic stage


(ˈproʊ təˌstoʊm)

any invertebrate in which the mouth appears before the anus during development, cleavage is spiral and determinate, and the coelom forms as a splitting of the mesoderm.
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References in periodicals archive ?
Identification and characterization of a protostome homologue of peropsin from a jumping spider.
ABSTRACT Molluscs belong to one of the two protostome superphyla, the Lophotrochozoa.
Peel, "Articulated Halkieriids from the Lower Cambrian of North Greenland and Their Role in Early Protostome Evolution," Philosophical Transactions of the Royal Society London B 347 (1995): 305-58.
Evidence from 18S ribosomal DNA that the Lophophorates are protostome animals.
It is conceivable that a twisting of the body organization would have turned a protostome into a deuterostome.
Eyes appear in the bilaterally symmetrical animals in the protostome invertebrate branch, including the Phylum Arthropoda (jointed leg animals), Annelida (segmented worms), and Mollusca (bivalves, snails, and cephalopods).
For example, the relationships among the protostome phyla or the classes of arthropods continue to be points of contention.
2008), use of these terms is problematic as both protostome and vertebrate genomes contain both types, a fact recognized by Hibino et al.
The seemingly sporadic distribution of the different SNBP types is the result of this transition having occurred repeatedly in the course of evolution (Kasinsky, 1995) within different groups of both the deuterostome and protostome branches (Ausio, 1999; Eirin-Lopez et al.
Moreover, analyses of marine invertebrates, particularly in understudied protostome lineages, help expand perspectives in gamete biology and add to our current knowledge of these topics, which is predominantly based on studies of mammals.
Although embryonic development in many annelid taxa conforms well to long-established protostome stereotypes, many species display modifications of the spiralian cleavage pattern, diverse modes of gastrulation, and of course varied larval forms.