What is "brachyura"

Brachyura \Brach`y*u"ra\, n. pl. [NL., fr. Gr. brachy`s short + o'yra` tail.] (Zo["o]l.) A group of decapod Crustacea, including the common crabs, characterized by a small and short abdomen, which is bent up beneath the large cephalo-thorax. [Also spelt Brachyoura.] See Crab, and Illustration in Appendix.