deuterostome

[doo-ter-uh-stohm, dyoo-]

noun

1. Embryology.,  a mouth that develops separately from the blastopore.

2. Taxonomy.,  any member of the phyla (Chordata, Hemichordata, Echinodermata, Chaetognatha) in which the anus appears first, developing at or near the blastopore, cleavage is radial and indeterminate, and the mesoderm and coelom form from outgrowths of the primitive gut.

deuterostome

1. Any of a major group of animals defined by its embryonic development, in which the first opening in the embryo becomes the anus. At this stage in their development, the later specialized function of any given embryonic cell has not yet been determined. Deuterostomes are one of the two groups of animals that have true body cavities (coeloms), and are believed to share a common ancestor. They include the echinoderms, chaetognaths, hemichordates, and chordates.

2. Compare protostome

Word History and Origins

Origin of deuterostome¹

First recorded in 1945–50; deutero- + -stome

Example Sentences

Some of the problems that once stalled progress — such as uncertainty over which groups belong in the deuterostome lineage of animals alongside chordates — have largely been resolved.

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But strangely, the new deuterostome fossils seem to have no anus, presumably using the mouth for evacuation.

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He told BBC News: "To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail as jaw-dropping. "We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves.

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Until now, the deuterostome groups discovered were from between 510 to 520 million years ago.

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Aspects of deuterostome phylogeny continue to be controversial, however, notably the position of the sessile pterobranchs among hemichordates, and the surprising association of Xenoturbella18 and acoelomorph flatworms with ambulacrarians19 proposed by some studies.

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