Hemichordata is a phylum of deuterostomeanimals, 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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... is spread out with 29.0% under the age of 18, 5.0% from 18 to 24, 29.0% from 25 to 44, 24.2% from 45 to 64, and 12.7% who are 65 years of age or older. The median ...