Hemichordata
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Acorn worm, a hemichordate. |
Scientific classification |
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Phylum: | Hemichordata
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Classes |
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- Graptolithina (extinct)
- Enteropneusta
- Pterobranchia
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The Hemichordata is a phylum of worm-shaped marine deuterostome animals, generally considered the sister group of the echinoderms. They date back to the Lower or Middle Cambrian and include an important class of fossils called graptolites, most of which became extinct in the Carboniferous.
Living hemichordates are a phylum with two living classes: the enteropneusts and the pterobranchs. Since the hemichordates are the closest living relatives to the chordates, they are of great interest to those studying the origins of chordate development.
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