Cheirocratidae Ren 2006

Cheirocratidae Ren, 2006

Cheirocratids Barnard & Barnard, 1983: 597, fig. 15.

Cheirocratidae Ren, 2006, 259.

Diagnosis. Eyes round. Antenna 1 not longer than the peduncle of antenna 2, with sparse slender setae. Antennae without calceoli. Mandible palp article 1 about 3 x longer than broad. Maxilliped outer plate large, longer than palp article 2, not longer than article 3. Coxae 1–3 large, all similar in size. Gnathopods 1–2 simple or subchelate. Pereopods 5–6 basis slightly expanded. Pereopods 6–7 similar in structure. Pereopod 5 shorter than pereopod 6. Urosomite 2, with mid-dorsal serration and simple or robust setae (except Incratella). Uropods 1–2, apices of rami with robust setae. Uropod 1 peduncle without basofacial robust seta. Uropod 3 biramous; peduncle long, at least 2 x as long as broad. Telson deeply cleft.

Included genera. Cheirocratidae includes 7 genera: Casco Shoemaker, 1930; Cheirocarpochela Ren & Andres, 2006; Cheirocratella Stephensen, 1940; Cheirocratus Norman, 1867; Degocheirocratus G. Karaman, 1985; Incratella Barnard & Drummond, 1982; Prosocratus Barnard & Drummond, 1982.

Remarks. Ren (2006) used the name Cheirocratidae and attributed the authorship to Barnard & Barnard (1983). However, Barnard & Barnard (1983), only referred to an informal group. Ren (2006) used the formal name Cheirocratidae, provided a diagnosis and therefore becomes the author of the family.

Cheirocratidae appears to be most similar to the Maeridae Krapp-Schickel, 2008. There are several significant differences between these taxa. In cheirocratids antenna 1 is shorter than the peduncle of antenna 2 whereas in the Ceradocus group it is subequal in length or longer than antenna 2. In general, gnathopod morphology is very different between these groups. For instance gnathopod 1 is almost always simple in male and female cheirocratids and subchelate in the Maeridae. Within the cheirocratids gnathopod 2 is usually simple in females and subchelate in males whereas in melitids it is subchelate in both sexes. In both families the male gnathopod 2 is usually larger than gnathopod 1. The shape of the anterior margin in the heads is also different. Although both families have an anteroventral notch, in the cheirocratids the anteroventral corner of the head is distinctively subquadrate.

An apparent autapomorphy that distinguishes cheirocratids from all other amphipods, except the Talitridae, is that antenna 1 is shorter than the peduncle of antenna 2. These shortened antennae appear to be independently derived in the two families. A second autapomorphy appears to be the significantly elongated first article of the mandibular palp, which can be up to 3 x as long as broad.

Incratella Barnard & Drummond, 1982 has always been considered to be the senior synonym of Cheirocratus (Indiocratus) Ledoyer, ‘1982’. It was unclear which taxon was published first. In fact the date of publication for Cheirocratus (Indiocratus) Ledoyer, ‘1982’ was actually January 1983 (Aberlenc (Ed, Faune de Madagascar), pers. comm.), thus Incratella has preference.