Icelus rastrinoides Taranetz in Smith 1935

Icelus rastrinoides Taranetz in Schmidt, 1935

[Japanese name: Tomikajika] (Figs 1–3; Tables 1, 2)

Icelus rastrinoides Taranetz in Schmidt, 1935: 416 (original description, key to the species based on unpublished data of A. Y. Taranetz; type locality: the Sea of Japan at the Cape of Cave and the Cape of Olympiad and at 45º05′N, 138º06′E; type locality based on lectotype designated herein: 45.086ºN, 138.100ºE, 230–411 m depth); Taranetz 1936: 150 (description; Sea of Japan); Matsubara 1955: 1138 (key; northern Sea of Japan); Nelson 1984: 29 (description; off Fukui, Japan); Lindberg and Krasyukova 1987: 193, fig. 119 (description, Sea of Japan); Parin et al. 2014: 255 (listed; Tatar Strait, Peter the Great Bay; northern Primorye, western Sakhalin Is., Russia); Fukuzawa et al. 2022: 6th page (comments; northern Sea of Japan).

Ricuzenius toyamensis Matsubara and Iwai, 1951: 86, fig. 1 (original description; type locality: Toyama Bay, Japan); Matsubara 1955: 1136 (key; Toyama Bay, Japan); Watanabe 1960: 22, pl. XVIII, fig. 1 (description; Toyama Bay and Yamagata, Japan); Lindberg and Krasyukova 1987: 186, fig. 114 [description and figure after Watanabe (1960); Toyama Bay and Yamagata, Japan].

Icelus toyamensis: Nakabo 1993: 553, 1301, unnumbered fig. (new combination, key; Niigata southward to Ishikawa, Japan); Nakabo and Kai 2013: 1167, 2062, unnumbered fig. (key; Yamagata southward to Ishikawa, Japan); Fukuzawa et al. 2022: 6 th page, fig. 4a–c (comparative materials; Yamagata southward to Fukui, Japan, and South Korea).

Lectotype (designated here). ZIN 21445, 90.9 mm SL, female, off Primorsky Krai, 45.086ºN, 138.100ºE, 230–411 m depth, coll. F. Derbek.

Paralectotypes. ZIN 56890 – 56891, 66.1–80.3 mm SL, 1 male and 1 female, same data as lectotype.

Other materials. Data of asterisked specimens from Fukuzawa et al. (2022). Toyama Bay, Japan: FAKU 13565, 72.6 mm SL, 1 male, off Uozu, Toyama, ca. 230 m depth; FAKU 14450 *, 130.0 mm SL, 1 female, holotype of Ricuzenius toyamensis, off Uozu, Toyama, ca. 230 m depth, coll. T. Iwai and H. Kinoshita, 15 October 1950; FAKU 14451 *, 14452 *, 14454, 145455 – 14457 *, 102.5–120.3 mm SL, 3 males and 3 females, paratypes of Ricuzenius toyamensis, same data as holotype; FAKU 14780 – 14782 *, 14784 *, 14785 *, 15418 *, 15419 *, 15421 – 15423 *, 15425 *, 70.4– 121.3 mm SL, 8 males and 3 females, off Uozu, Toyama. West of Noto Peninsula, Japan: FAKU 99204, 76.0 mm SL, 1 female, 37.771ºN, 136.394ºE, 240 m depth, 17 June 2011; FAKU 132575 – 132580 *, 58.3–66.3 mm SL, 2 males and 4 females, 37.429ºN, 136.206ºE, 250 m depth, 16 June 2010; FAKU 145613 – 145615 *, 57.8–97.9 mm SL, 2 males and 1 female, 37.295ºN, 136.170ºE, 331 m depth, 22 June 2016; FAKU 147906 *, 94.8 mm SL, 1 female, 37.406ºN, 136.321ºE, 251 m depth, 18 June 2020; ZUMT 32015 *, 84.1 mm SL, 1 male, ZUMT 32022 *, 84.9 mm SL, 1 male, ZUMT 32025 *, 83.4 mm SL, 1 female, off Fukui, no further data. Off Niigata to Yamagata, Japan: FAKU 134922, 101.9 mm SL, 1 female, no further data; FAKU 140280 – 140282, 142243, 142244, 143214, 143215, 79.6–93.8 mm SL, 4 males and 3 females, 38.573ºN, 138.412ºE, 310 m depth, 23 July 2015; FAKU 142239, 83.5 mm SL, 1 female, 38.616ºN, 138.409ºE, 287 m depth, 23 July 2015; FAKU 145632, 2 males and 2 females, 71.7–83.5 mm SL, 38.584ºN, 138.409ºE, 311 m depth, 10 July 2016; FAKU 145680 – 145682, 145684, 145685, 65.1– 101.9 mm SL, 2 males and 3 females, 38.619ºN, 138.413ºE, 291 m depth, 9 July 2016; FAKU 147842 – 147849 *, 147850, 68.1–84.0 mm SL, 3 males and 6 females, 39.147ºN, 138.786ºE, 345 m depth, 27 July 2020. West of Hokkaido, Japan: FAKU 200875 – 200879, 83.4–98.0 mm SL, 2 males and 3 females, 45.001ºN, 140.439ºE, 256 m depth, 20 May 2013; FAKU 201202 – 201208, 201210, 64.6–71.5 mm SL, 2 males and 6 females, 44.835ºN, 140.517ºE, 224 m depth, 19 May 2013. East of Korean Peninsula: FAKU 149086, 85.0– 97.4 mm SL, 1 male and 3 females, 37.283ºN, 132.250ºE, 240 m depth; NIBR-P 16324 *, 90.4 mm SL, 1 male, off Goseong-gun, Gangwon-do, Korea; NIBR-P 4791 *, 1 male and 1 female, 79.2 and 117.5 mm SL, Uljin-gun, Gyeongsanbukdo, Korea.

Diagnosis. A species of Icelus with the following combination of characters: supraocular and parietal spines absent; nuchal spine blunt, indistinct, covered with skin; uppermost preopercular spine unbranched; mid-sized scales scattered (not in rows) above and below lateral line; belly naked; minute ctenoid scales on upper part of maxillary; lateral line scales large, tubular, bearing spinules on dorsal and posterior margins; lower jaw slightly protruding anteriorly; spines of first dorsal fin 8 or 9; rays of second dorsal fin 18–22; anal-fin rays 16–20; pectoral-fin rays 17–20.

Description. Counts and measurements shown in Table 1. Data for lectotype presented first, followed by data of other materials in parentheses (if different). Body subcylindrical anteriorly and slightly compressed posteriorly; dorsal profile rounded below first dorsal fin, gradually sloping posteriorly (Fig. 1). Head robust, slightly depressed. Eye large, upper margin just below dorsal contour. Interorbital space almost flat or weakly depressed. Occipital region concave, rounded, without knob or ridge. Nasal spine short, sharp, directed posterodorsally. Anterior nostril with short tube level with lower margin of pupil; posterior nostril narrow, on anterior margin of orbit. Nuchal spine indistinct (indistinct or forming a blunt ridge), directed posterodorsally. Supraocular and parietal spines absent. Suborbital stay bearing a minute spine posteriorly or a blunt ridge. Maxilla extending to below posterior margin of pupil; lower jaw slightly protruding anteriorly. Small conical teeth on jaws, vomer and palatines, forming a narrow band. Four sharp unbranched preopercular spines; uppermost spine directed posterodorsally, second posteriorly, third and lowermost ventrally. Supraocular cirrus present in both sexes; parietal and nuchal cirri absent (present or absent). Branchiostegal membranes broadly united, forming a fold over isthmus. Gill rakers on first gill-arch short, round, covered with minute prickles; no rakers in angle between ceratobranchial and epibranchial.

* Damaged in one specimen.

Snout, interorbital space, opercle, and dorsolateral surface of head from suborbital stay covered with small scales with serrated margins. Minute ctenoid scales on upper portions of eye and maxillary. Ventral surface of head naked. Scales on lateral line large, tubular, bearing spinules on dorsal and posterior margins; lateral line scales extending past posterior edge of hypural plate. Mid-sized scales with spinules scatted above and below lateral line, not arranged in distinct rows on trunk, posteriorly forming a single indistinct row (1–3 indistinct rows) on caudal peduncle above and below lateral line; small scales scattered dorsally (Fig. 2A–C). Bases of first and second dorsal fins naked. Pectoral axilla with mid-sized scales (not in distinct rows) (Fig. 2D–F). Chin and belly without scales.

First dorsal fin originating above dorsal edge of gill slit; tips slightly protruding; first dorsal proximal pterygiophore bearing first and second spines. First and second dorsal fins separated by short interspace. Second dorsal fin of similar height to first dorsal fin; tips free from membranes; rays unbranched. Anal fin originating slightly posterior to level of second dorsal-fin origin; rays unbranched. Caudal fin truncate. Pectoral fin large, upper half shallowly emarginate, 11th (11th or 12th) rays longest, extending beyond anal-fin origin; all rays unbranched. Pelvic fin with one spine and three rays, spine and outermost ray closely united; below first dorsal-fin origin. Male urogenital papilla distinct, cylindrical with large curved terminal appendage, located below posterior half of first dorsal fin.

Cephalic sensory system (based on FAKU 14450 and other non-type materials, Fig. 3). Supraorbital canal with anterior and posterior nasal pores (NA and NP), cluster of supplementary pores posteriorly NA; supraorbital pores SO1–5 present, SO5 forming a cluster of small pores; anterior and posterior coronal pores (CA and CP) present. Infraorbital canal with eight pores (IOP1–8); IOP1–2 large and oval, IOP 7–8 somewhat small, of similar size to supplementary pores along margins of infraorbital canal. Postorbital canal with four pores (T1–4); T1 without distinct canaliculus, T3 and T4 with long canaliculus. Occipital canal with anterior and posterior medial pores (OCA and OCP), and posterior lateral central pore (OCLP); anterior and posterior lateral pores (OLA and OLP), and anterior lateral central pore (OCLA) present or absent. Preoperculo-mandibular canal with ten pores (PM1–10); PM1 on right and left sides separated.

Coloration when fresh (based on FAKU 99204, Fig. 1E). Head and body brown or yellowish-brown, lightening ventrally; body scales whitish, forming mottled markings. Anterior half of jaws black; indistinct black blotches below eye; two faint dark brown saddles below second dorsal fin; caudal peduncle dark brown. Nostril tube brown; head cirri dark brown. First and second dorsal fins light brown with indistinct oblique dark brown bands; anal fin brown, distal part darker in males; caudal fin with faint pale brown vertical stripes; pectoral fin pale basally, a black blotch on base; pelvic fin whitish.

Coloration in alcohol (Fig. 1A–D). Head and body uni-formly brown, becoming somewhat lighter ventrally (two faint dark brown saddles below second dorsal fin). Anterior half of jaws dark brown; indistinct black blotches below eye; caudal peduncle somewhat darker. Nostril tube brown; head cirri brown or light brown. First and second dorsal fins light brown with indistinct oblique dark brown bands; anal fin brown, distal part darker in males; caudal fin with faint pale brown vertical stripes; pectoral fin pale basally, a dark blotch on its base; pelvic fin light brown.

Distribution. Known from the Sea of Japan, west of the Noto Peninsula northward to west of Hokkaido, Japan, and east of the Korean Peninsula northward to Primorsky Krai (Fukuzawa et al. 2022; this study).

Geographic variations. Icelus rastrinoides exhibits extensive geographic variations in dorsal- and anal-fin ray counts (Table 2). The specimens from the northern Sea of Japan off Primorsky Krai and Hokkaido, and east of the Korean Peninsula (Areas A–C in Fig. 4) had somewhat higher counts than those from the Sea of Japan coast of Honshu Is., Japan (Areas D–F in Fig. 4). Dorsal-fin ray counts differed significantly between the specimens from Areas B and E, C and D, and C and E, with those of the anal-fin rays being likewise between the specimens from Areas B and D, B and E, C and D, C and E (P <0.01). Along the Sea of Japan coast of Honshu Is., a north-south cline was apparent, the above counts gradually increasing from south to north (Table 2). In addition, the dorsal-fin spine numbers differed slightly between the specimens from Areas B and F (P = 0.05). However, counts of pectoral-fin rays and pored lateral line scales did not differ statistically among the above geographic areas (P > 0.01).