Australorchestia Serejo & Lowry, 2008

Lowry, J. K. & Springthorpe, R. T., 2015, Coastal Talitridae (Amphipoda: Talitroidea) from north-western Australia to Darwin with a revision of the genus Cochinorchestia Lowry & Peart, 2010, Zootaxa 3985 (2), pp. 151-202 : 154-155

Australorchestia Serejo & Lowry, 2008

Australorchestia Serejo & Lowry, 2008: 163 .

Type species. Australorchestia occidentalis Serejo & Lowry, 2008 , original designation.

Included species. Australorchestia includes 2 species: A. occidentalis Serejo & Lowry, 2008 ; A. tantabiddyensis sp. nov.

Diagnostic description (based on male). Head Eyes medium (greater than 1/5 to 1/3 head length). Antenna 1 short, not longer than article 4 of antenna 2 peduncle. Antenna 2 peduncular articles slender to slightly incrassate; peduncular article 3 without ventral process; final flagellar article large, cone-shaped, forming virgula divina. Mandible left lacinia mobilis 4- 5-dentate. Maxilliped palp article 2 distomedial lobe well developed; article 4 reduced, button-shaped. Gnathopod 1 chelate; posterior margin of carpus and propodus each with lobe covered in palmate setae. Gnathopod 2 subchelate; merus and carpus free; dactylus attenuated distally.

Pereopods 3–7 cuspidactylate. Pereopods 5–7 without setae along posterior margin of dactylus. Pereopods 6–7 not sexually dimorphic; without row of short setae along posterior margin of dactyli. Pleonites 1–3 without dorsal spines. Pleopods all well developed, biramous. Epimera 1–3 without vertical slits. Uropod 1 rami without apical pear-shaped setae; outer ramus slender, with marginal robust setae. Uropod 3 well developed; ramus subequal in length to peduncle. Telson apically incised, as broad as long or longer than broad with 5–6 robust setae per lobe.

Remarks. In the original description of Australorchestia occidentalis the male antenna 2 is considered to be slightly incrassate, the left lacinia mobilis has 4 cusps, the male gnathopod 1 is considered as subchelate and the male pereopod 7 is considered to be slightly expanded. In the new species, A. tantabiddyensis , male antenna 2 is slender to slightly incrassate, the left lacinia mobilis has 5 cusps, in the male gnathopod 1 the palm of the propodus is acute but then forms a sharp angle to become obtuse so that the gnathopod is considered as chelate, and the pereopod 7 has the merus and propodus slightly expanded as in A. occidentalis . The generic diagnosis has been amended to document these changes.

The relationship of Australorchestia to other talitrid genera is unclear. The obtuse palm on gnathopod 1 is unusual among talitrids. Australorchestia is most similar to Africorchestia Lowry & Coleman, 2011 . Both genera have a reduced, button-shaped maxillipedal palp article 4, palmate lobes on the carpus and propodus of male gnathopod 2, well developed pleopods, robust setae on the outer ramus of uropod 1 and 5–10 robust setae per lobe on the telson . They differ in the chelation of gnathopod 1, the distal shape of the dactylus of male gnathopod 2, the sexual dimorphism of pereopods 6 and 7 and the condition of the dorsum of pleonites 1–3. Both genera are considered to be post-Gondwanan.