Pasiphaea gracilis Hayashi, 1999

[New Japanese name: Akahoshi-shira-ebi]

Figs. 7B, 9

Pasiphaea gracilis Hayashi, 1999: 290, figs. 15–17 [type locality: New Caledonia, 850 m].— De Grave & Fransen 2011: 258.

Material examined. T/RV “Toyoshio-maru”, 2005-04 cruise, stn 7, NE of Tokashiki Island, Kerama Islands,

26°19.38’N, 127°26.78’E, 593– 532 m, 26 May 2005, beam trawl, 4 males (cl 9.4–10.9 mm), 1 female (cl 10.7 mm), CBM-ZC 11339; 2010-03 cruise, stn 8, N of Zamami Island, Kerama Group, 26°19.03’N, 127°28.07’E, 550–628 m, 23 May 2010, sledge, 2 ovigerous female (cl 10.6, 11.1 mm), CBM-ZC 11269; stn 13, W of Amamiohshima Island, 28°23.54’N, 129°11.25’E, 0–508 m, bottom depths 683–708 m, 21 May 2010, ORI net oblique tow, 4 females (cl 8.4–10.2 mm), CBM-ZC 11279.

Coloration in fresh condition (Fig. 7B). Body generally semitransparent, with scattered red chromatophores; dorsal and ventral margins of pleomere 6, telson and uropods reddish. Basal halves of fingers of pereopods 1 and 2 also reddish.

Distribution. Previously known from the South-West Pacific Ocean, i.e., Chesterfield Islands, New Caledonia, Wallis and Futuna Islands, and Indonesia; at depths of 600–1300 m (Hayashi 1999). The present specimens greatly extend the geographical range of the species to the north and west.

Remarks. Pasiphaea gracilis was originally described on the basis of material from the South-West Pacific localities, including Chesterfield Islands, New Caledonia, Wallis and Futuna Islands, and Indonesia, and referred to the P. sivado species group (Hayashi 1999). There have been no subsequent records of the species. The specimens examined in this study are identified as P. gracilis on account of the following features (cf. Hayashi 1999): rostrum moderately small and moderately ascending (Fig. 9A, B); carapace dorsally rounded, with shallow but distinct branchiostegal sinus (Fig. 9A, B); pleomeres all rounded dorsally, pleomere 6 with posterodorsal spine (Fig. 9C); posterior margin of telson truncate; meri of pereopods 1 and 2 with 4–8 and 10–15 spiniform setae, respectively (Fig. 9D, E), included within variation range previously reported; ischium of pereopod 2 without spiniform seta on ventral margin (Fig. 9B); and no pleurobranch on thoracomere 8. Our specimens represent the second record of the species since the original description.

Pasiphaea japonica Omori, 1976 was the only member of the P. sivado species group known from Japan prior to this study. It is readily distinguished from P. debitusae and P. gracilis by the possession of a small pleurobranch on the thoracomere 8 and the more numerous spiniform setae on the pereopod 2 merus (14–23 in number). Pasiphaea mclaughlinae Hayashi, 2006a, recently described from Taiwan and referred to the P. sivado species group, resembles P. gracilis, but the former is characteristic within the species group in having dorsally flat tergites of the pleomeres 3–5 (Hayashi, 2006).

Specimens in one of the three lots (CBM-ZC 11279) were collected together with specimens of P. debitusae (CBM-ZC 11278). The two species can be distinguished from each other by the shape of the rostrum (broader and more ascending in P. gracilis than in P. debitusae), the development of the branchiostegal sinus of the carapace (clearly defined in P. gracilis versus obsolescent in P. debitusae), the armature of the ischium of the pereopod 2 (unarmed in P. gracilis versus armed with one spiniform seta in P. debitusae), as well as the different coloration in life: the scattered red chromatophores are distributed all over the pleon in P. gracilis, while they are not present on the dorsal side in P. debitusae.

From Japanese waters, the following seven species of Pasiphaea have been reported (Hayashi 2007; Komai & Komatsu, 2016): P. amplidens Spence Bate, 1888, P. exillimanus Komai, Lin & Chan, 2012, P. japonica, P. oshoroae Komai & Amaoka, 1993, P. sinensis Hayashi & Miyake, 1971, P. sinrekoi Burukovsky, 1987, and P. tarda Krøyer, 1845. Of them the specific identity of specimens identified as P. tarda needs to be reassessed (Hayashi, 2006b). With the addition of P. debitusae and P. gracilis, nine species of Pasiphaea are now known from Japan.