ANOMURA MACLEAY, 1838

Wicksten, Mary K., 2012, Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces 3371, Zootaxa 3371, pp. 1-307 : 141-142

INFRAORDER ANOMURA MACLEAY, 1838

The most recent attempt to analyze the systematics of the families of the Anomura and organize them into superfamilies was that of McLaughlin et al. (2007). This system, using a combination of morphological and cladistic analysis, is followed in the current work. Many problems in distinguishing relationships between the various anomurans remain unsolved because of different conclusions based on molecular versus morphological data, examination of only a few specimens in a taxon or over-generalization of the significance of particular features during development. Older works combined the old infraorder Thalassinidea (now the Axiidea and Gebiidea ) with the Anomura , but sufficient molecular and morphological evidence supports their removal from the Anomura .

Most anomurans in the northeastern Pacific and adjacent waters are crab-like. The carapace is not fused to the epistome (the area above the mouth). In many species, the second antennae are elongated instead of short, and are not retractable into sockets. Often, one pair of antennae lies mesial to the eyestalks and the other lateral to them. In the hermit crabs, king crabs and galatheoids, the third maxillipeds do not form a plate-like covering of the mouth (an operculum). Pereopod 1 is chelate in all local species but Emerita analoga . Pereopod 5 often is modified for digging, gripping a shell or cleaning the body. The abdomen may be soft, twisted to one side or partially membranous, but not among the mole crabs. Pleopods often are reduced or present on only one side of the abdomen. The telson may be reduced or absent, or form part of a tail fan. Unlike true crabs ( Brachyura ), anomurans may be able to swim by flapping the abdomen.

In anomurans and brachyurans, the term "spine" refers to any sharply pointed process and a "tooth" is either flattened or rounded.