Coelorinchus fuscigulus Iwamoto, Ho & Shao, 2009

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 51-55

Coelorinchus fuscigulus Iwamoto, Ho & Shao, 2009

[Japanese name: Shima-sokodara]

( Figs. 28 E–F, 35–36; Appendix 3-2B)

Coelorinchus cingulatus (not Gilbert & Hubbs 1920): Shao et al. 2008b: table 2 (listed; in part, 1 spec. from northeastern Taiwan, 400–600 m).

Coelorinchus cylindricus (not Iwamoto & Merrett 1997): Shao et al. 2008b: table 2 [1 spec. listed from northeastern Taiwan (as first record from Taiwan )].

Coelorinchus fuscigulus Iwamoto, Ho & Shao, 2009:40 , figs. 1–2 [original description; holotype: ASIZP 70169 , from Tashi (= Da-xi), northeastern Taiwan; 9 paratypes from north eastern Taiwan]; Nakabo & Kai 2013:508 (in key; Japan; new Japanese name “Shima-sokodara”); Iwamoto et al. 2015:55 (brief description based on type specimens); Motomura 2020:38 (listed; Japan).

Diagnosis. Ventral light organ externally represented by long dark line, terminated with 1 fossa at each end, one immediately anterior to anus, the other on chest just posterior to isthmus (duct connecting each fossa often difficult to distinguish). Underside of head completely naked except along lateral nasal ridges; dorsal surface of snout mostly scaled, but prominent naked clefts present along each side of median rostral ridge; occipital area between parietal ridges without prominent naked area. Snout long, sharply pointed, length 60–72% PRL; dorsal profile of snout almost straight to gently concave in lateral view; terminal scute short, arrowhead-shaped, dorsoventrally flattened, length 14–21% PRL; distal portion of snout narrowly attenuated when viewed dorsally; lateral nasal ridge incompletely supported by nasal bone. Interdorsal space less than first dorsal-fin base length. Anal fin originating posterior to vertical through second dorsal-fin origin. First dorsal fin high, but second spinous ray not especially elongate, height of fin 80–106% PRL. Second dorsal fin well developed, its rays as long as opposites of anal fin. Anus immediately anterior to anal-fin origin. Premaxillary teeth small, slender, conical in short, uniformly wide band, with outer series slightly enlarged; posterior end of tooth band falling far short of lateral corner of mouth. Body scales covered with short, reclined, needle-like spinules in subparallel to slightly divergent rows; spinules in each row greatly overlapping, but free from one another, with last spinule extending well beyond posterior scale margin; buttresses scarcely developed.Orbit diameter40–43% PRL; postorbital length 58–61% PRL; orbit–preopercle distance 55–61% PRL; upper-jaw length 41–46% PRL; preoral length 50–64% PRL; body depth at first dorsal-fin origin 84–90% PRL; isthmus–anal distance 132–158%; length of gill slit 20– 23% PRL; barbel length 13–17% PRL. Transverse scale rows below first dorsal-fin midbase 5.5–7.5. Spinules on scales anterior to light organ not rudimentary.About 8–11 dark saddles on body (often faint in large specimens); scale pockets outlined in black; underside of head dark to dusky, heavily peppered; lips pale; oral cavity, and gular and branchiostegal membranes prominently blackish; first dorsal fin dark, with white apical tip; pelvic fin dark, but outermost ray paler distally.

Material examined. 13 specimens. Holotype of Coelorinchus fuscigulus: ASIZP 70169 (76.8 mm HL, 322+ mm TL), Da-xi fish market, Yilan, northeastern Taiwan , bottom trawl, coll. H.-C. Ho, 23 Mar. 2007 . Paratypes of C. fuscigulus: ASIZP 63249 (1, 56.1 mm HL, 238 mm TL), Da-xi fish market, Yilan , bottom trawl, coll. H.-C. Ho, 21 Mar. 2004 ; ASIZP 70168 (1, 77.4 mm HL, 300+ mm TL), CAS 228337 (2, ex. ASIZP 70168 , 69.3–74.1 mm HL,283+–303+ mmTL), Da-xi fish market, Yilan, bottom trawl, coll. H.-C. Ho, 29 Jan. 2007 ; ASIZP 66922 (1, 66.5 mm HL, 286 mm TL), off northeastern Taiwan, Okinawa Trough , 24.8500ºN, 122.0333ºE, 536 m, R/ V Ocean Researcher I, sta. CP248, French-type beam trawl, coll. H.-M. Yeh et al., 28 Aug. 2004 ; ASIZP 66973 (1, 72.8 mm HL, 291 mm TL), Nan-fang-ao fish market, Yilan , bottom trawl, coll. H.-C. Ho, 26 Jan. 2007 ; CAS 228338 [1, ex. CAS 224583 (in part), 65.8 mm HL, 293+ mm TL], Nan-fang-ao fish market, Yilan, bottom trawl, coll. H.-C. Ho, 30 Aug. 2005 ; ASIZP 63193 (1, 53.7 mm HL, 226 mm TL), CAS 224492 (1, ex. ASIZP 63193 , 44.4 mm HL, 189 mm TL), off Senkaku Island, Okinawa Trough , 25.75ºN, 123.48ºE, bottom trawl, coll. H.-C. Ho, 24 Apr. 2004 . Non-types: Japan: KAUM-I. 55534 (1, 65.0 mm HL, 265+ mm TL), northwest of Kuro-shima Island , 30.9877ºN, 129.5725ºE, 300–400 m, coll. Y. Fukui and M. Matsunuma, 16 Jul. 2013 ; BSKU 106760 (1, 41.9 mm HL, 174+ mm TL), southeast of Shimokoshiki-jima Island, East China Sea , 31.5658ºN, 129.8915ºE, 380 m, F/ V Maruko-maru, tr. 1, bottom trawl, coll. N. Nakayama et al., 24 Apr. 2012 . Taiwan: * BSKU 108968 (1, 67.2 mm HL, 295+ mm TL), Da-xi fish market, Yilan, bottom trawl, coll. N. Nakayama and M.-Y. Lee, 25 Jul. 2012 .

Counts and measurements. Based on 12 specimens (41.9–77.4 mm HL, 174+–322+ mm TL). Counts: first dorsal-fin rays II,8–9; pectoral-fin rays i16–i18; pelvicfin rays 7; gill rakers on first arch (outer/inner) 0/7–9, on second arch 5–6/7–9; longitudinal scales 30–36; transverse scale rows below first dorsal-fin origin 6.5–8.5, below first dorsal-fin midbase 5.5–7.5, below second dorsal-fin origin 6–8, above anal-fin origin 21.5–22.5; pyloric caeca 19.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 37–42 (60–72); orbit diameter 24–26 (40–43); postorbital length 34–38 (58–61); postrostral length 58–63; orbit–preopercle distance 33–38 (55–61); suborbital width 12–14 (20–23); upper-jaw length 25–27 (41–46); length of rictus 18–21 (31–36); length of premaxillary tooth band 10–13 (16– 21); preoral length 31–38 (50–64); length of terminal snout scute 9–12 (14–21); length of lateral nasal ridge 25–30 (40–52); length of suborbital ridge 89–92 (143– 158); snout width 18–28 (31–48); internasal width 17– 21 (26–36); interorbital width 20–23 (33–38); occipital width 9–11 (15–18); body width over pectoral-fin bases 36–48 (61–78); body depth at first dorsal-fin origin 49– 56 (84–90); body depth at anal-fin origin 40–48 (66–79); prepelvic length 103–112 (169–185); preanus length 150–165 (245–270); preanal length 144–169 (243–277); isthmus–pelvic distance 29–37 (49–59); isthmus–anus distance 80–96 (134–152); isthmus–anal distance 79–100 (132–158); pelvic–anal distance 45–68 (75–111); anusanal distance 4 (6–7); pelvic-fin length 36–44 (58–74); pectoral-fin length 39–45 (64–76); predorsal length 106– 114 (178–187); height of first dorsal fin 50–66 (80–106); length of first dorsal-fin base 17–23 (28–38); interdorsal length 10–14 (15–24); length of gill slit 12–14 (20–23); length of posterior nostril 7–9 (11–15); barbel length 8–11 (13–17).

Description of Japanese specimens. General features are shown in Figs. 35–36 . Body slender, deepest below first dorsal-fin origin, progressively tapering into long, laterally compressed tail. Trunk subcylindrical in cross section, width across pectoral-fin bases about 1.2 in depth below first dorsal-fin origin. Head large, shallow, HL about 4.1–4.2 in TL. Snout long, sharply pointed, protruding well beyond upper jaw, length 1.7 times as long as orbit diameter; dorsal profile almost straight in lateral view, but gently upturned near tip; ventral surface slightly inflated when fresh, but concave in preserved specimens; lateral nasal ridge incompletely supported by nasal bone; anterolateral margins of snout slightly convex when viewed dorsally. Orbit large, oval in outline, greatest diameter about 1.4–1.5 in postorbital length. Interorbital space broad, slightly concave in preserved specimen, width 1.2 in orbit diameter. Mouth moderate in size, inferior, protrusible; upper-jaw length about equal to orbit diameter; anterior margin of upper lip below anterior nostril; posterior margin of maxilla extending to below hind 1/3 of orbit; lateral corner of mouth slightly restricted by lip folds; lips slightly papillose near teeth. Suborbital region narrow, sharply divided in dorsal and ventral parts by longitudinal ridge passing from tip of snout to posterior angle of preopercle. Preopercle large, moderately lobed posteroventrally; hind margin oblique, forming angle of about 60º to horizontal axis of head and body. Interopercle completely hidden behind preopercle. Subopercle produced as slender tip posteroventrally. Gill membranes thick, broadly connected across isthmus, with narrow posterior free fold. Gill opening narrow, not reaching forward to vertical through hind margin of orbit. Outer gill slit moderately restricted by skin folds, length 1.8–2.1 in orbit diameter. Gill rakers developed into small, spinous tubercles, but those on epibranchial somewhat pad-like; no rakers on outer side of first arch and inner side of fourth arch. Chin barbel short, terminating as fine tip, length 2.6–2.7 in orbit diameter.

Anus immediately anterior to anal-fin origin. Two dermal fossae of light organ on midventral line of abdomen; anterior fossa oval, situated midway between isthmus and line connecting inner bases of pelvic fin; posterior window small, scarcely discernible, located just anterior to anus.

Teeth small, conical, gently incurved, in bands in both jaws; outer series slightly enlarged, followed by progressively smaller teeth medially. Premaxillary band short, almost uniformly broad, about 5-teeth wide anteriorly, extending to posterior 2/3 of rictus. Mandibular teeth in narrow tapered band, about 4-teeth wide near symphysis; posterior margin of tooth band nearly reaching lateral corner of mouth.All teeth deeply embedded in gum papillae.

Body scales moderately large, thin, somewhat deciduous; those on dorsum below interdorsal space covered with short, slender, needle-like spinules in 6–7 subparallel to slightly divergent, ridge-like rows ( Fig. 28E ); middle row longest but spinules not especially high or enlarged; spinules reclined about 25º to scale surface and greatly overlapping; spinules in each row not adjoined to one another, forming reclined comb-like ridges; height of spinules increasing posteriorly, with last in each row extending well beyond posterior scale margin; lateral buttresses of spinules poorly developed; no reticulate structures on unexposed potion. Scales on isthmus much smaller than those on dorsum, covered with much thicker spinules arranged in 4–6 subparallel rows ( Fig. 28F ). Scales becoming cycloid on light organ, beneath gill cover, and posterior to pectoral and pelvic fins. Body uniformly scaled, but all fins naked.

Scales on head ridges thickened, weakly spinulated; those on median rostral ridge covered with divergent rows of spinules. Terminal snout scute short, arrowheadshaped, dorsoventrally flattened, its length 2.0 in orbit diameter. Supraoccipital scute rudimentary; posttemporal scutes thickened, elongated, armed with 1–2 rows of spinules. Scales on head generally similar to those on body, but variable in size and spinulation. Occipital scales covered with long, erect, needle-like spinules in narrowly divergent rows; spinules in each row free from one another, forming comb-like ridges, and height of spinules gradually increasing posteriorly; scales on dorsal surfaces of snout posterior to leading edges armed with small cluster of similar spinules. Other scales on head similar to those on body, but spinules arranged in parallel to subparallel rows; those on gill cover and between parietal and postorbital ridges largest. Nasal fossa narrowly scaled ventrally. Dorsal surfaces of snout mostly scaled, but narrow Y-shaped clefts along each side of median rostral ridge naked. Nape between occipital ridges without prominent naked area. Underside of head completely naked, except for characteristic overlapping scales along lateral nasal ridges.

No open pores along cephalic sensory canals. Small, elongated free neuromasts serially arranged along ventral surfaces of infraorbital canals (prominently marked when fresh). Anterior nostril small and circular; posterior large, elongated slit; septum between nostrils forming anteriorly opened hood. Grooved lateral line well developed, not interrupted throughout.

Origins of first dorsal and pelvic fins slightly posterior to vertical through pectoral-fin base; first dorsal fin moderately high, its height 2.8 times as long as its base length; second spinous ray not elongated, almost entirely smooth along its leading edge (small fine spine present near tip in BSKU 106760); its tip extending to base of 7th–9th rays of second dorsal fin when laid back. Interdorsal space equal to half length of first dorsal-fin base. Origins of second dorsal and anal fins on about same vertical. Outer pelvic-fin ray prolonged as fine distal tip, reaching posterior fossa of light organ or beyond when laid back.

Color when fresh ( Fig. 35 ). Ground color of head and body purplish gray dorsally, paler ventrally; abdomen tinged with blue in ventral view; anterior and posterior fossae of light organ marked with dark blue; about 8 broad dark saddles on trunk and tail; anteriormost saddle located at level of first dorsal-fin origin; second saddle faint, diagonal, extending from second dorsal-fin origin to pectoral-fin base; bands farther posterior generally broader and prominent; upper part of opercle much darker than surroundings; lips pale; underside of head generally dusky, heavily peppered, but lower preopercles paler; branchiostegal membranes dull black behind gill apparatus; first dorsal fin dark with white apical tip; pectoral fin pale with blackish uppermost ray; pelvic fin dark, but outermost ray white; second dorsal and anal fin pale to dusky; small intense black spot at origin of first dorsal fin and each base of pectoral and pelvic fins.

Color in alcohol ( Fig. 36 ). Almost same as in fresh condition; oral and gill cavities blackish; gill rakers and arches dusky, filaments yellowish brown.

Size. To about 30 cm TL ( CAS 228337 , paratype, 303+ mm TL, Da-xi , northern Taiwan).

Distribution. Restricted to Japan and Taiwan (Appendix 3-2B). So far known only from the Okinawa Trough and northern South China Sea at depths of 380– 536 m ( Iwamoto et al. 2009; this study). Very rare in Japanese waters.

Remarks. The original description given by Iwamoto et al. (2009) is excellent and can also be referred to for details. Coelorinchus fuscigulus was originally described from 10 specimens collected from the East China Sea ( Fig. 36 ), some of which were initially reported as C. cylindricus Iwamoto & Merrett, 1997 by Shao et al. (2008b: table 2). Interestingly, C. fuscigulus was not recorded by previous Japanese ichthyologists, despite their extensive collecting efforts in the East China Sea (e.g., Okamura & Kitajima 1984; Okamura 1985; Yamada 1986; Shinohara et al. 2005; Yamada et al. 2007; Furuhashi et al. 2010). Iwamoto et al. (2009) indicated the collection site of CAS 224492 (paratype, 44.4 mm HL) as “25º75′N, 123º48′E, Diaoyutai Archipelago, Yilan, Taiwan ” [sic], but the coordinates fall inside Japan’s EEZ (it should also be read as 25.75ºN, 123.48ºE).Accordingly, Nakabo & Kai (2013) subsequently proposed a Japanese name “Shima-sokodara” for the species. Two additional Japanese specimens are herein recorded from the East China Sea off Kagoshima Pref., one of which from off Shimokoshiki-jima Island (BSKU 106760, 41.9 mm HL; Fig. 35 A–C) represents the northernmost record and the smallest specimen of C. fuscigulus .

The presence of dark saddles dorsally on the body is one of the important diagnostic features of C. fuscigulus . While these saddles are prominent in small specimens ( Fig. 35A ), they are often indistinct in large adults ( Fig. 35D ).

Relationships and comparisons. Coelorinchus fuscigulus is one of 10 species of the C. hubbsi group (see the Relationships of C. brevirostris ), and closely resembles the following three species: C. cylindricus Iwamoto & Merrett, 1997 known from New Caledonia and New Zealand; C. melanosagmatus Iwamoto & Anderson, 1999 widely distributed in the Indian Ocean; and C. multifasciatus Sazonov & Iwamoto, 1992 represented by only the holotype collected from the Sala y Gomez Ridge. They share the presence of similar body markings consisting of more than six dark saddles on the body, and the absence of a large dark blotch between the lateral line and the pectoral-fin base. Coelorinchus fuscigulus is distinguished from these three species by having more scales below the midbase of the first dorsal fin (5.5–7.7 vs. 4.5, 4–5, and 5 in C. cylindricus , C. melanosagmatus , and C. multifasciatus respectively) and a greater body depth at the first dorsal-fin origin (84–90% PRL vs. 77%, 62–83%, and 81% respectively). It further differs from C. cylindricus in having a smaller orbit (40–43% PRL vs. 46%), longer postorbital (58–61% PRL vs. 55%) and upper-jaw (41–46% PRL vs. 36%) lengths, a greater orbit–preopercle distance (55–61% PRL vs. 50%), and a wider outer gill slit (20–23% PRL vs. 18%). It also differs from C. melanosagmatus in having a shorter snout (60– 72% PRL vs. 74–95%), greater orbit–preopercle (55–61% PRL vs. 48–54%) and isthmus–anal (132–158% PRL vs. 90–118%) distances, and a longer chin barbel (13–17% PRL vs. 7–13%). The holotype of C. multifasciatus (ZMMGU P.18117, 32.3 mm HL; examined here) is much smaller than the C. fuscigulus specimens examined (41.9–77.4 mm HL), which makes comparisons of their morphometric characters difficult. However, C. fuscigulus differs notably from that species in lacking prominent naked areas along each side the median rostral ridge and atop the head between the parietal ridges (vs. present in C. multifasciatus ).

Figures

FIGURE 28. Scanning electron micrographs showing body scales of three species of the Coelorinchus hubbsi group. (A–B) C. brevirostris, FFNU P-640, 52.6 mm HL; (C–D) C. cingulatus, BSKU 98963, 60.4 mm HL; (E–F) C. fuscigulus, BSKU 106760, 41.9 mm HL. (A, C, E) Scales from the dorsum below the interdorsal space; (B, D, F) from the chest between the isthmus and the anterior tip of the light organ. Views from above. [Photos: N. Nakayama]

FIGURE 35. Fresh specimens of Coelorinchus fuscigulus. (A–C) BSKU 106760, 41.9 mm HL, 174+ mm TL, southeast of Shimokoshiki-jima Island, Kagoshima Pref., East China Sea, 380 m depth; (D) BSKU 108968, 67.2 mm HL, 295+ mm TL, Da-xi fish market, northeastern Taiwan, East China Sea. (A, D) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. [Photos: (A–C) N. Nakayama; (D) M.-Y. Lee]

FIGURE 36. Holotype of Coelorinchus fuscigulus. ASIZP 70169, 76.8 mm HL, 322+ mm TL, Da-xi fish market, northeastern Taiwan, East China Sea. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]