protostome

[ proh-tuh-stohm ]

noun

, Zoology.

1. any member of the lower invertebrate phyla 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.

protostome

/ prōt′tə-stōm′ /

1. Any of a major group of animals defined by its embryonic development, in which the first opening in the embryo becomes the mouth. At this stage of development, the later specialization of any given embryonic cell has already been determined. Protostomes are one of the two groups of animals having a true body cavity (coelom) and are believed to share a common ancestor. They include the mollusks, annelids, and arthropods.
2. Compare deuterostome

Word History and Origins

Origin of protostome¹

proto- + -stome

Example Sentences

Since these genes are not clustered in available protostome genomes, there is no evidence for deeper bilaterian ancestry.

From Nature

These similarities reveal features of bilaterian and/or metazoan genomes that have been lost or diverged in many protostome genomes reported so far, and thus enable a more complete reconstruction of genomic features of the last common ancestors of protostomes, bilaterians and metazoans, including gene and chromosome structure and organization.

From Nature

The conservation of 17bilaterian ALGs among , and various deuterostomes implies that the last common protostome and deuterostome ancestors also had this organization.

From Nature

The brain of the ragworm Platynereis dunerlii, a protostome, was found to contain C-opsins.

From Scientific American

“We’ve been using the name protostome for 100 years, and now it’s clear that it doesn’t mean anything.”

From Scientific American