Science Fair Project Encyclopedia
Hemichordata
- Enterepneusta
- Pterobranchia
- Planctosphaeroidea
Hemichordata is a phylum of deuterostome animals, generally considered the sister group of our own, the chordates. 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. One surviving species is known, Cephalodiscus graptolitoides .
All other modern forms are marine worms, commonly called acorn worms . They are divided into two classes: the Enteropneusta and the Pterobranchia . The phylum contains less than 100 species.
10-26-2009 08:16:03
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The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details