Ezotinorchestia solifuga (Iwasa, 1939) comb. nov.

[Japanese name: Kita-okatobimushi]

(Figs 1–3)

Orchestia solifuga Iwasa, 1939: 271–273, fig. 12, pl. 14;? Sidorov and Barabanschikov 2010: 71–73, figs 1–5.

Non Orchesita traskiana Stimpson, 1857: Bulycheva 1957: 166, fig. 60.

“ Parorchestia ” solifuga (Iwasa, 1939): Bousfield 1984: 207.

Non Platorchestia solifuga (Iwasa, 1939): Miyamoto 1984: 3.

“ Orchestia ” solifuga Iwasa, 1939: Morino et al. 2009: 26; Morino 2015: 1076 (fig. 1), 1087.

Material examined. Male 12.9 mm (NSMT-Cr 24220), male 12.4 mm (NSMT-Cr 24219), female 13.3 mm (NSMT-Cr 24221), male, 3 ovig. females, and 2 females (NSMT-Cr 24222), 8 males and 71 females (H. Miyamoto collection); Utoro, Abashiri (base of a cliff, under litter); 1 August 1988; H. Miyamoto coll. Female 12.4 mm (NSMT-Cr 24217), 2 males, 2 ovig. females, and 3 females (NSMT-Cr 24218), 14 males and 9 females (H. Miyamoto collection); On-neto, Nemuro (forest of a shrine, under litter); 2 August 1988; H. Miyamoto coll. 2 females (NSMT-Cr 24223), 5 males and 24 females (H. Miyamoto collection); Rausu (near entrance of the Nature Park, floor of birch forest); 1 August 1988; H. Miyamoto coll. Male 9.2 mm (NSMT-Cr 24224), ovig. female 9.2 mm (NSMT-Cr 24225), ovig. female (NSMT-Cr 24226), 2 males and 2 females (NSMT-Cr 24227); Senhoshi, Rishiri Is. (Picea and Abies forest, 25 m alt.); 31 July 2007; M. Sato and K. Ishii coll. Male and juvenile (NSMT-Cr 24228); Kafukai, Rebun Is. (Abies forest, 20 m alt.); 31 May 2007; H. Miyamoto and K. Ishii coll.

Description of male (NSMT-Cr 24220, 12.9 mm). Antenna 1 (Fig. 1A, B) with peduncular article 3 distinctly longer than either article 1 or 2; flagellum with 6 articles. Antenna 2 (Fig. 1A), peduncular article 5 subequal to articles 3 and 4 combined in length, flagellum with 19 articles. Mouthparts (Figs 1C, D, 2 A–F) as in generic diagnosis. Gnathopod 1 (Fig. 2G) with merus bearing small pellucid lobe, carpus ca. 1.3 times as long as propodus, with prominent pellucid lobe, propodus with submarginal row of 6 robust setae, surface of anterodistal corner scabrous (Fig. 2H). Gnathopod 2 (Fig. 2I) with propodus distally smoothly broadened, palm smooth, as long as posterior margin, dactylus weakly attenuate. Locking robust setae of pereopods 3–7 reduced (Fig. 3 A–E). Dactylus of pereopod 4 pinched (Fig. 3B). Bases of pereopods 5–7 (Fig. 1A) shallowly rounded posteriorly. Merus and carpus of pereopod 7 slender, similar to those of pereopod 6.

Pleonite side plates (Fig. 3F) weakly acuminate posteriorly, with several setae on posterior margins. Peduncles of pleopods 1–3 (Fig. 3 G–I) with facial and marginal robust setae, occasionally with plumose setae; rami developed, with ca. 8 articles, 0.98, 0.96, and 1.06 times as long as respective peduncles. Uropod 1 (Fig. 3J) with peduncle bearing 5 outer, 3 and 1 tiny inner marginal robust setae; outer ramus with 4 marginal robust setae, inner ramus with 4 outer and 4 dorsomarginal robust setae. Uropod 2 (Fig. 3K) with peduncle bearing 4 outer marginal and 6 inner-medial marginal robust setae, outer ramus with 3 marginal robust setae, inner ramus with 3 outer marginal (distalmost one closely set to apical robust setae) and 2 dorsomarginal robust setae. Uropod 3 (Fig. 3L) with peduncle bearing 7 robust setae from dorsal to ventrodistal margin, ramus short, 0.71 times as long as peduncle, with 5 marginal and ca. 8 distal setae. Telson (Fig. 3M) with 10–11 robust setae per lobe.

Description of female (NSMT-Cr 24221, 13.3 mm). Gnathopod 1 (Fig. 2J) with carpus ca. 1.5 times as long propodus, propodus lacking scabrous surface. Gnathopod 2 (Fig. 2K) with basis almost parallel-sided, merus with small lobe with scabrous surface, propodus with ca. 4 submarginal setae. Oostegites of pereopods 2 and 5 respectively with 25 and 13 simple-tipped marginal setae (Fig. 3N, O, P).

Distribution. The present species is terrestrial and was collected from under litter of coastal forests of eastern Hokkaido and islands off northern Hokkaido (Fig. 4). The original description was based on the material from Akkeshi near Kushiro, in Hokkaido (Iwasa 1939).

Remarks. The present material accords well with the original description given by Iwasa (1939), except for the number of robust setae on the telson. Five specimens examined in the present study with body lengths of 9.2–12.9mm bear 8–12 robust setae per lobe whereas the material from Akkeshi displays 5–6 robust setae (Iwasa 1939: pl. 14, fig. x). Although the body length of the depicted specimen was not specified by Iwasa (1939), the difference in the number of setae is very likely related to body size, since the variation in the number of the setae among the five specimens grossly parallels their body length. The gnathopod 1 of male in this species exhibits a prominent pellucid lobe on the carpus, and the scabrous surface on anterodistal part of the propodus, both of which could be additional generic diagnoses.

Sidorov and Barabanschikov (2010) described a female of Orchestia solifuga from “subsurface” water of the Samarga River estuary, northern Primorye, Russia, but the depigmented body, diffuse ocelli, elongate mandible, and peculiar robust setae on the posterior margin of the merus-carpus of pereopod 3 of the Russian material strongly suggest they actually had a different species. Proper generic allocation of this specimen requires further examination of the gnathopods of the males. In terrestrial coastal habitats in Hokkaido, Kokuborchestia kokuboi (Uéno, 1929), Ditmorchestia ditmari (Derzhavin, 1923), and Ezotinorchestia solifuga occur. Kokuborchestia kokuboi is found in the southeast (Morino and Miyamoto 2015a) whereas E. solifuga inhabits the northern to eastern coast (Fig. 4). Ditmorchestia ditmari is confined to a small area in the east (Morino and Miyamoto 2015b), possibly representing the southern-most population of this species, which ranges north to Kamchatka.

The reproductive season of the Rishiri population is estimated to be from July to September, and the egg number per female is around 14 (Morino et al. 2009).