Hemichordata

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, which went extinct in the Carboniferous. Modern forms are
marine worms, commonly called acorn worms. They are divided into two
classes: the Enteropneusta and the Pterobranchia.

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