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.

Published as part of Lowry, James Kenneth, 2017, Hermesorchestia alastairi gen. et sp. nov. from Australia (Talitridae: Senticaudata: Amphipoda: Crustacea), pp. 491-506 in Zootaxa 4311 (4) on page 492, DOI: 10.11646/zootaxa.4311.4.3, http://zenodo.org/record/848363