Small, mostly marine creatures that look like tiny lobsters with elongate bodies a few millimeters in length and conspicuous claws. Most live either in tunnels or in mucous tubes cemented together from particles of detritus. The body is subcylindrical or flattened dorsoventrally and is divided into three sections. Have six pereonites, at least one jointed uropod branch, and a pair of pincers or true chelae on the chelipeds.

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