Demaorchestia, Lowry & Myers, 2022

Lowry, J. K. & Myers, A. A., 2022, Platorchestiinae subfam. nov. (Amphipoda, Senticaudata, Talitridae) with the description of three new genera and four new species, Zootaxa 5100 (1), pp. 1-53 : 11

Demaorchestia gen. nov.

Type species. Platorchestia . parapacifica Kim, Jung & Min, 2013 .

Included species. Demaorchestia contains 5 species: Demaorchestia hatakejima sp. nov.; D. joi ( Stock & Biernbaum, 1994) comb. nov.; D. mie sp. nov.; D. parapacifica ( Kim, Jung & Min, 2013) comb. nov.; D. pseudojoi sp. nov..

Ecological type. Beach-hoppers or Marsh-hoppers.

Habitat. Sandy beaches, often around river mouths.

Etymology. Demao is the type locality of D. pseudojoi plus stem Orchestia .

Diagnostic description (male). Based on Kim & Kim (1987) and Miyamoto & Morino (2004).

Head. Antenna 2 peduncular articles incrassate; article 3 without ventral process. Mandible left lacinia mobilis 5-cuspidate. Labium with or without inner lobes, with possible vestigial inner lobes. Maxilliped palp article 2 with distomedial lobe; article 4 reduced, button-shaped.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; posterior margin of carpus and propodus each with lobe covered in palmate setae; propodus anterior margin with 4 groups of robust setae, ‘subtriangular’ with welldeveloped posterodistal lobe, palm transverse; dactylus simplidactylate. Gnathopod 2 subchelate; propodus palm acute, rounded distally, irregular or sigmoidal, with small mid-palmar sinus, without large distal sinus; dactylus not modified distally, blunt. Pereopods 3–7 dactyli bicuspidactylate. Pereopod 4 significantly shorter than pereopod 3; carpus significantly shorter than that of pereopod 3; dactylus amplidactylate, thickened proximally with notch midway along posterior margin or short with mini-wavy posterior margin. Pereopod 6 subequal in length to pereopod 7 or slightly shorter; not incrassate, male merus and or carpus expanded; basis moderately expanded; male merus and carpus not expanded or male merus expanded, carpus not expanded. Pereopod 7 incrassate or not; basis broadly expanded; posterior margin with distinct minute serrations, each with a small seta, posterodistal lobe present, shallow, broadly rounded; merus unexpanded or merus expanded distally, subtriangular, anterior margin slightly convex; carpus unexpanded or expanded, subrectangular, shorter than or subequal to propodus; propodus broad or slender; length 5.8–7.2 × width; propodus without large distal tuft of setae. Oostegites (female) setae with simple smooth tips.

Pleon. Pleopods 1–3 all well-developed. Uropod 1 peduncle distolateral robust seta present or absent; exopod without marginal robust setae; endopod with marginal robust setae in 2 rows. Uropod 2 exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 2 rows. Uropod 3 ramus subequal to or shorter than peduncle. Telson apically incised, with 7–11 robust setae per lobe.

Remarks. Demaorchestia is one of several genera having an incrassate second antenna. Within this group it is most similar to Platorchestia . It differs in having a simplidactylate gnathopod 1. Demaorchestia differs from Cocorchestia in having a distally rounded acute palm on the second gnathopod, never with a large distal sinus and the endopod of the uropods with two rows of marginal setae.

Distribution. Russia, Korea, Japan, Taiwan ( Gurjanova 1951, Jo 1988, Kim & Kim 1987, Miyamoto & Morino 2004).