Eorchestia Bousfield, 1984

Lowry, J. K. & Baldanzi, S., 2016, New talitrids from South Africa (Amphipoda, Senticaudata, Talitroidea, Talitridae) with notes on their ecology, Zootaxa 4144 (2), pp. 151-174 : 164-169

Eorchestia Bousfield, 1984

Eorchestia Bousfield, 1984: 202 .

Type species. Parorchestia rectipalma K.H. Barnard, 1940 , original designation.

Diagnosis. Head eye unknown. Antenna 1 long, subequal in length to antenna 2 peduncle. Antenna 2 slender, less than half body length; peduncular article 3 without plate or process ventrally. Mandible left lacinia mobilis 4-cuspidate ( Bousfield 1984: 7). Maxilliped palp article 2 distomedial lobe present; article 4 small, well defined. Gnathopod 1 subchelate; sexually dimorphic; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; dactylus subequal in length to propodus. Gnathopod 2 subchelate. Pereopods 3–7 simplidactylate (not confirmed). Pereopod 4 dactylus shape unknown. Pereopod 5 dactylus shape unknown. Pereopods 6–7 not sexually dimorphic; dactylus without setae along posterior margin. Pleonite 1–3 without dorsal spines. Pleopods well developed. Epimera 1–3 without slits just above ventral margins. Uropod 1 outer ramus without marginal robust setae. Uropod 3 ramus subequal in length or slightly longer than peduncle, without marginal robust setae. Telson tapering distally with 2 apical robust setae per lobe.

Included species. Eorchestia includes 2 species: E. rectipalma ( K.H. Barnard, 1940) ; E. dassenensis ( K.H. Barnard, 1916) .

Remarks. The genus Eorchestia is part of a group of five basal talitrid taxa which includes Chiltonorchestia Bousfield, 1971 , Cochinorchestia Lowry & Peart, 2010 , Eorchestia, Bousfield, 1984 , Microrchestia Bousfield, 1984 and Protorchestia Bousfield, 1982 . They are defined by: antenna 1 long, reaching at least to the midpoint of peduncular article 5 of antenna 2; maxilliped palp article 4 reduced in size but distinct; gnathopod 1 subchelate with palmate lobes on the posterior margin of the merus, carpus and propodus; pereopods simplidactylate and the telson with two apical robust setae per lobe. They are all considered to be post-Gondwanan genera in the sense of Lowry & Springthorpe 2015b and all appear to be very closely related, usually separated by only one or two generic level characters.

Eorchestia rectipalma ( K.H. Barnard, 1940) , type species of the genus, was originally particularly poorly described. K.H. Barnard’s (1940) illustrations show a sexually dimorphic subchelate gnathopod 1 with palmate lobes on the merus, carpus and propodus in the male, but only on the carpus and propodus in the female. Richardson (1993) shows palmate lobes on merus, carpus and propodus for both sexes of the Tasmanian species E. palustris and E. rupestris and a subchelate male second gnathopod with an apically blunt dactylus.

Bousfield (1984) in the original description of Eorchestia , gave no indication of material examined and no new illustrations, but he said that he had several other species from New Zealand and south-eastern Australia under study. Bousfield (1984) added a number of generic level characters in defining the genus: lacinia mobilis with four cusps; maxilliped palp article 2 distomedial lobe well developed and article 4 distinct; and uropod 1 outer ramus without marginal robust setae. The problem is that it is not clear what material these characters were based on. Based on the key in Griffiths (1976) one can infer that pereopod 7 is not sexually dimorphic, then Eorchestia separates from other talitrid genera.

The inclusion of E. palustris Richardson, 1993 and E. rupestris Richardson, 1993 from Tasmania is problematic. The factual characters indicate that the Tasmanian species has non-sexually dimorphic first gnathopods (sexually dimorphic in the South African species). This character aligns the Tasmanian species with Microrchestia Bousfield, 1984 and Eorchestia palustris and E. rupestris are here moved to Microrchestia .