[Crustacea, general] The first (basal) podomere of protopodite.

[Amphipoda] (Abbr. CX) An immovable flat plate inserted into the lateral surface of the pereonite (pereon segment), and sometimes fused to it (in hyperiids). In gammarids the coxa may be enlarged, forming a lateral shield (Bathystegocephalus globosus 1), while in other suborders it is always small. Other articles may broaden in different ways or be elongated, more or less narrow and with parallel margins. Articles 5-7 or 6-7 sometimes form the chela or subchela, especially on the gnathopods, but sometimes on other pereopods as well. However, prehensile pereopods are not always present, and all pereopods are simple in many amphipods. Prehension is usually accomplished in hyperiids by pressing article 6 (provided with a small dactyl) against an expanded article 5; whereas in gammarids (and in some hyperiid cases as well) the strong dactyl presses against an expanded article 6. In chelate pereopods the palm, the part of surface or margin of the article on which subsequent article(s) close(s) for the purpose of prehension, is located on the distally produced carpal process (Oxycephalus clausi 1). In subchelate pereopods the carpal process is lacking, and the palm located on the distal or posterior margin of the article (Stenopleura atlantica 1, Primno brevidens 1).

Alternative forms for coxa : Coxae (pl.), [Amphipoda] CX (abbrev.), [p][/p].