Ezotinorchestia Morino & Miyamoto 2016, gen. nov.

Genus Ezotinorchestia gen. nov.

[New Japanese name: Kita-okatobimushi zoku]

Type species. Orchestia solifuga Iwasa, 1939.

Diagnosis. Body size medium. Eyes medium. Antenna 1 elongate, reaching mid-point of peduncular article 5 of antenna 2, peduncle subequal to flagellum in length, peduncular article 3 longer than either article 1 or 2. Antenna 2 in male not incrassate, flagellum subequal to peduncle in length. Upper lip lacking robust setae. Lacinia of left mandible 4-dentate. In maxilliped, outer margin of precoxa not stepped, palp articles 2 and 3 broad and mediodistally lobate, article 4 reduced.

Gnathopod 1 sexually dimorphic, male propodus deeply subchelate, carpus and propodus each with broad-based pellucid lobe, merus with small pellucid lobe, lateral surface of propodus with rows of submarginal and facial robust setae; in female, pellucid lobe or scabrous surface both absent, propodus palm vertical, shorter than dactylus. In gnathopod 2 of male, propodus powerfully subchelate, dactylus slightly attenuate; in female, mitten-shaped, basis weakly expanded anteroproximally, propodus with facial and submarginal setae on lateral surface. Pereopods cuspidactylate (bi-cuspate), locking robust setae of propodi reduced. Coxa of pereopod 4 as deep as wide. Posterior lobe of coxa of pereopod 6 smoothly curved. Pereopod 7 in male not sexually dimorphic. Coxal gills of pereopods 2 and 6 larger than those of pereopods 3–5, gill of pereopod 2 lobed, others convoluted, gill of pereopod 6 distally linguiform.

Pleonite side plates lacking marginal pits; pleopodal peduncles with 2 retinacula, arrays of robust setae both marginally and facially, and well-developed rami. Uropod 1 with distolateral robust seta of peduncle shorter than subdistal one; inner ramus with outer and dorsal marginal robust setae, outer ramus with marginal robust setae. Uropod 2 with rami subequal in length and marginal robust setae in 1 or 2 rows. Uropod 3 with peduncle slightly expanded; ramus stout, shorter than peduncle. Telson wider than long, with dorsolateral, distolateral, and distal robust setae, 6–12 setae in total per lobe.

Oostegites subovate, with numerous simple or slightly curve-tipped setae.

Etymology. The generic name is a combination of the ancient name for the region of Hokkaido, Ezoti, and part of the generic name Orchestia.

Remarks. There are three genera of terrestrial coastal talitrids in the northwest Pacific: Ezotinorchesita gen. nov., Kokuborchestia Morino and Miyamoto, 2015, and Ditmorchestia Morino and Miyamoto, 2015. They show several morphological similarities among themselves. Ezotinorchestia is close to Kokuborchestia in having 1) an elongate antenna 1, 2) a deeply subchelate and lobed merus-carpus in male gnathopod 1, 3) well-developed pleopods, 4) outer ramus of uropod 1 with robust setae marginally, 5) laterally to distally distributed robust setae on the telson, and 6) simple-tipped setae on the oostegites. However, Kokuborchestia displays: 1) a similar gnathopod 1 in both sexes, with a deep palm and lobed merus-carpus (vs. sexually dimorphic), 2) the coxal gill of pereopod 6 being broad and distally truncate (vs. distally linguiform), 3) densely setose (with plumose setae) peduncles of the pleopods (vs. with robust setae), and 4) the telson lobe with 5–6 robust setae (vs. 6–12). These are all regarded as generic difference. Ditmorchestia displays similarities to Ezotinorchestia in having: 1) a sexually dimorphic gnathopod 1, 2) a setose outer ramus of uropod 1(with robust setae), and 3) a setose telson lobe (also with robust setae). However, the shorter antenna 1, the produced basis of pereopod 7, the moderately reduced pleopods, and the robust ramus of uropod 3 in Ditmorchestia separate this genus from Ezotinorchestia.

Males of Orchestia Leach, 1814, as redefined by Lowry and Fanini (2013), and Cryptorchestia Lowry and Fanini, 2013, distributed mostly in the North Atlantic, show similar features to the present new genus in having: 1) a deeply subchelate gnathopod 1, 2) well developed pleopods, and 3) robust setae on the outer ramus of uropod 1. In addition, the lobed merus of gnathopod 1 is shared by Cryptorchestia and the present genus, while a high number of robust setae on telson (7+) is common to Orchestia and the present genus. However, both Orchestia and Cryptorchestia are separable from Ezotinorchestia by the shorter antenna 1, which does not exceed the end of peduncular article 4 of antenna 2. It should also be noted that recent molecular analyses of Orchestia and related species from the Mediterranean and northeast Atlantic suggest polyphyly of the genus Orchestia (Pavesi et al. 2015). Future molecular studies with extended species sampling could lead to further revision of the diagnosis of Orchestia.