Tongorchestia, Lowry, J. K. & Bopiah, Arundathi, 2013

Lowry, J. K. & Bopiah, Arundathi, 2013, The talitrid amphipods of Tonga (Crustacea, Amphipoda, Talitridae), Zootaxa 3681 (4), pp. 347-370 : 359

Tongorchestia gen. nov.

Type species. Tongorchestia towneri sp. nov.

Included species. Tongorchestia contains 2 species: T. pangaimotu sp. nov.; T. towneri sp. nov.

Etymology. Named for the type locality Tonga in combination with the ‘ orchestia ’ stem.

Diagnostic description (based on male). Antenna 1 short, rarely longer than article 4 of antenna 2 peduncle. Antenna 2 peduncular articles incrassate (expanded). Mandible left lacinia mobilis 4-dentate. Maxilliped palp article 2 distomedial lobe well developed, article 4 reduced, button-shaped. Gnathopod 1 subchelate; posterior margin of carpus and propodus each with lobe covered in palmate setae. Gnathopod 2 subchelate; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; dactylus not modified distally or spatulate distally. Pereopods 3–7 cuspidactylate. Pereopod 4 dactylus thickened proximally with a notch midway along posterior margin. Pereopods 6–7 not sexually dimorphic. Pleonite 1–3 without dorsal spines. Pleopods all well developed. Epimera without stridulating organ just above ventral margins. Uropod 1 outer ramus with marginal robust setae. Uropod 3 ramus shorter or subequal in length to peduncle. Telson entire, with 7–13 robust setae per lobe.

Remarks. Without a phylogenetic analysis it is difficult to know the relationship of Tongorchestia to other talitrid genera. Based on apparent apomorphies such as a reduced article 4 on the maxillipedal palp, an incrassate male second antenna, cuspidactylate pereopods and a high number of robust setae (7–13) on the telson , Tongorchestia is similar to Platorchestia (groups 1 and 2). It differs from both in having four teeth on the left lacinia mobilis, marginal robust setae on the outer ramus of uropod 1 and a relatively long ramus on uropod 3.

If the presence of marginal robust setae on the outer ramus of uropod 1 is considered, then based on apomorphies such as mandible with 4 teeth, vestigial fourth article on the maxillipedal palp and male gnathopod 1 with palmate lobes on the carpus and propodus, Tongorchestia is similar to Orchestia , but Tongorchestia differs in having an incrassate antenna 2.