Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta (acorn worms), and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. Th...
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http://en.wikipedia.org/wiki/Hemichordate
any of a group of wormlike marine invertebrates closely related to the chordates and sometimes considered to constitute a phylum, Hemichordata. The ... [5 related articles]
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http://www.britannica.com/eb/a-z/h/35
a group of animals first found in the Burgess Shale which have bodies very similar in arrangement to the chordates, but without the central stiffening rod (notochord)
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