Hermesorchestia, Lowry, 2017

Lowry, James Kenneth, 2017, Hermesorchestia alastairi gen. et sp. nov. from Australia (Talitridae: Senticaudata: Amphipoda: Crustacea), Zootaxa 4311 (4), pp. 491-506 : 492

Hermesorchestia gen. nov.

Diagnostic description (based on male). Head eye medium size (greater than 1/5 to 1/3 head length). Antenna 1 long, reaching midpoint or slightly beyond end of antenna 2 peduncle. Antenna 2 peduncular articles slender, article 3 without plate or process ventrally, flagellum apical article minute, virgula divina present. Mandible left lacinia mobilis with 4 cusps. Labrum epistome with many robust setae. Maxilliped precoxa ventral margin smooth; palp article 2 distomedial lobe well developed; article 4 fused with article 3. Gnathopod 1 subchelate; posterior margin of carpus and propodus each with lobe covered in palmate setae. Gnathopod 2 subchelate; dactylus not distally modified, apically acute. Pereopods 3–7 bi-cuspidactylate; without setae along posterior margin of dactylus. Pereopod 4 significantly shorter than pereopod 3; dactylus dissimilar to dactylus of pereopod 3, thickened proximally or notched midway along posterior margin. Pereopod 5 dactylus long, slender. Pereopod 6 sexually dimorphic merus and carpus expanded in males. Pereopod 7 sexually dimorphic, basis, merus and carpus variously expanded in males; merus developed as a 3-dimensional structure. Pleonite 3 with or without dorsal spines. Pleopods 1–3 reduced, rami unsegmented. Epimera 1–3 ventral margins without slits. Uropod 1 outer ramus with single facial/outer row of marginal robust setae. Urosomite 3 subrectangular, deeper than broad. Uropod 3 peduncle dorsally concave, margin accommodating telson. Telson with notch and dorsal midline, broader than long, laterally and apically margins convex with 10+ lateral, apical and dorsal robust setae.

Etymology. From the stem Orchestia and Hermes, the Greek wing-footed messenger god, in reference to the expanded pereopods 7 articles. Gender masculine.

Type species. Hermesorchestia alastairi sp. nov., original designation by monotypy.

Remarks. Sexual dimorphism of the male pereopods 6 and 7 occurs in around 18% of talitrid genera ( Bousfield 1982, 1984). The shape and form of pereopods 6 and 7 in Hermesorchestia gen. nov. is novel to the group. Such extreme pereopod enlargement/expansion in relation to overall body size is also seen in Africorchestia Lowry & Coleman, 2011 . In Hermesorchestia pereopod 7 is the largest pereopod where the basis, merus and carpus are grossly developed, while in Africorchestia pereopod 6 is extremely elongate and only the basis is expanded. The male pleonite 3 dorsal projections which develop in only some male H. alastairi gen. et sp. nov. individuals, is also seen in Africorchestia and Capeorchestia Lowry & Baldanzi, 2016 , however these projections are always present in the latter two genera. To-date these are the only three talitrid genera of the ~73 documented which have dorsal projections.

The presence of robust setae on the labrum is also known for Bellorchestia Serejo & Lowry, 2008 , a genus found in southern Australia, including Tasmania. The presence of palmate lobes on the distal margins of the carpus and propodus of gnathopod 1 separates Hermesorchestia from Bellorchestia where the lobes are only present on the propodus, the latter state being rare within the family Talitridae .