Transorchestia Bousfield, 1982

Transorchestia Bousfield, 1982: 19 .— Serejo & Lowry, 2008: 164, table 1.

Type species. Orchestia chiliensis Milne Edwards, 1840 .

Included species. Transorchestia includes four species: Trans. chiliensis (Milne Edwards, 1840); Trans. marlo Serejo & Lowry, 2008; Trans. miranda (Chilton, 1916); Trans. serrulata (Dana, 1852a) .

Diagnostic description (male). Expanded from Bousfield (1982); Varela (1983).

Head. Eye medium (1/5–1/3 head length). Antenna 1 short, rarely longer than peduncular article 4 of antenna 2. Antenna 2 peduncular articles incrassate (expanded); article 3 without plate or process ventrally. Upper lip epistome without robust setae. Mandible left lacinia mobilis 4-cuspidate. Maxilliped outer margin of precoxa not stepped; palp article 2 with distomedial lobe; article 4 reduced, button-shaped.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; palm acute or transverse. Gnathopod 2 subchelate; propodus palm acute; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; dactylus not modified distally, blunt; shorter than propodus. Pereopods 3–7 bi-cuspidactylate. Pereopod 4 dactylus thickened proximally with notch midway along posterior margin. Pereopod 5 dactylus long, slender, not inflated. Pereopod 6 sexually dimorphic (merus and carpus expanded); shorter than pereopod 7 (slightly). Pereopod 7 sexually dimorphic. Pereopod 7 sexually dimorphic, merus broad, carpus expanded, subrectangular.

Pleon. Pleonites 1–3 without dorsal spines. Oostegites setae with curled tips. Pleopods 1–3 all well-developed. Epimera 1–3 slits absent. Uropod 1 peduncle distolateral robust seta absent; rami without apical spear-shaped setae; exopod with marginal robust setae in one row; endopod with marginal robust setae in 1 row. Uropod 2 rami without apical spear-shaped setae; exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 2 rows. Uropod 3 ramus shorter than peduncle. Telson longer than broad, tapering distally, apically incised, with marginal and apical robust setae, with 7 to 9 robust setae per lobe.

Remarks. Transorchestia is a distinctive genus based on the incrassate antenna 2, palmate lobes on the merus, carpus and propodus of gnathopod 1 and 7–9 robust setae per lobe on the telson.

The sexually dimorphic pereopods 6 and 7 are defining characters for Transorchestia, distinguishing it from Orchestia which has only pereopod 7 as sexually dimorphic.

Distribution. South America. Cape Horn district (Milne Edwards 1840). Australia (Serejo & Lowry 2008). New Zealand (Chilton 1916; Dana 1852a).