Cochinorchestia, Lowry & Peart, 2010

Lowry, J. K. & Peart, R., 2010, The genus Microrchestia (Amphipoda: Talitridae) in eastern Australia, Zootaxa 2349 (1), pp. 21-38 : 21-22

Cochinorchestia gen. nov.

Microrchestia Bousfield, 1984: 202 (in part).

Type species. Parorchestia notabilis K.H. Barnard, 1935 .

Etymology. The generic name uses the geographic name Cochin from the local area and the stem Orchestia.

Diagnosis. Antenna 1 elongate, longer than antenna 2 peduncle. Mandible left lacinia mobilis unknown. Maxilliped palp article 2 with medial lobe; dactylus well developed. Gnathopod 1 subchelate to chelate; posterior margins of merus, carpus and propodus each with lobe covered in palmate setae. Gnathopod 2 subchelate in male, mitten-shaped in female. Pereopods 6–7 sexual dimorphism not known. Pleopods well developed. Uropods 1–2 outer ramus with robust setae. Uropod 3 ramus shorter than peduncle. Telson entire, with 2 to 4 apical setae.

Included species. Cochinorchestia notabilis (K.H. Barnard, 1935) .

Remarks. Although Cochinorchestia notabilis (K.H. Barnard, 1935) is not well described there is enough known about the taxon to recognise that it is not a species of Microrchestia or apparently any other known genus of talitrid. Based on the illustrations of Griffiths (1973) C. notabilis has a remarkably well developed first antenna for a talitrid, similar to species of Microrchestia .

The genera differ as follows: maxillipedal palp article 2 with medial lobe and article 4 well developed in Cochinorchestia (palp article 2 without medial lobe and article 4 small, but distinct in Microrchestia ); uropods 1–2 outer ramus with robust setae in Cochinorchestia (uropods 1–2 outer ramus without robust setae in Microrchestia ).

If the development of maxillipedal palp article 4 and the setation of the outer ramus of uropod 1 is ignored then Cochinorchestia and Microrchestia would be considered as sister taxa. This is interesting because at the time the Indian Ocean began to form, the ancestor of these taxa would have existed in Gondwana. Apparently the resulting taxa that evolved in isolation in Sahul ( Australia /New Guinea) reduced the maxillipedal palp article 4 and lost the setae on the outer ramus of uropods 1 and 2 and the taxa that evolved in India and eastern Africa retained them. Currently 37 of the 55 known genera have lost the marginal robust setae on the outer ramus of uropod 1. If this is character is homoplastic, then it is a powerful phylogenetic indicator within the monophyletic talitrids.

It is possible that the population of C. notabilis from south-eastern India described by K.H. Barnard (1935) and the population from Moçambique described by Griffiths (1973) are different species. Although the male gnathopod 2 palms are very similar, the shape of the protuberances along the palms are different. This might be due to different growth stages. K.H. Barnard’s (1935) specimen was 9–10 mm long, but Griffiths (1973) does not give a length for his specimen.

Distribution. The genus Cochinorchestia is currently known from southern India and Moçambique on the west coast of Africa.