Coelorinchus hexafasciatus Okamura, 1982

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 60-63

Coelorinchus hexafasciatus Okamura, 1982 [Japanese name: Musuji-sokodara]

( Figs. 40–41 , 42 A–B; Appendix 3-2D)

Coelorhynchus hexafasciatus Okamura, 1982:173 , fig. 104 (original description; holotype: BSKU 31443 , from Kyushu-Palau Ridge, 26º45.0ʹN, 135º19.0ʹE, in 336 m; 31 paratypes from Kyushu-Palau Ridge, in 685–910 m; new Japanese name: “Musuji-sokodara”).

Coelorinchus hexafasciatus: Okamura 1984b:97 , pl. 83, fig. G (compiled); Okamura 1988:97, pl. 83, fig. G (compiled); Okamura 1997:127, fig. 16 (compiled); Nakabo & Kai 2013:512 (in key; Japan); Iwamoto et al. 2015:56, fig. 6 (brief description; 1 spec. from Da-xi; first record from Taiwan); Motomura 2020:38 (listed; Japan).

Coelorinchus hexfasciatus [sic]: Iwamoto 1990:159, fig. 374 (synopsis).

Caelorinchus hexafasciatus : Nakabo 1993:371 (in key; Japan); Nakabo 2000:435 (in key; Japan); Nakabo 2002:435 (in key; Japan).

Diagnosis. Light organ externally represented by short, narrow, naked streak immediately anterior to anus, its anterior margin falling far short of line connecting inner pelvic-fin bases. Underside of head completely naked except for oval scaly patches on ventral surfaces of preopercles; naked clefts along each side of mid rostral ridge scarcely developed. Snout long, deep, length 57– 70% PRL, its dorsal profile almost straight in lateral view; tip of snout not sharply pointed, with 3 bluntly pointed scutes; lateral nasal ridge incompletely supported by nasal bone. Anus slightly separated from anal-fin origin. Premaxillary teeth in long, tapered band, with outer series prominently enlarged; posterior margin of tooth band almost reaching lateral corner of mouth. Body scales covered with short, reclined, keel-like spinules in widely divergent, fine saw-toothed ridges; every spinule row complete, extending to posterior scale margin; spinules in each row overlapping, but generally free from one another, gradually increasing in height posteriorly; buttresses poorly developed. Occipital scales covered with narrowly divergent rows of spinules. Preoral length 41–58% PRL; barbel length 10–18% PRL. About 6–7 dark saddles on body; underside of head dusky; lips pale; oral cavity blackish; gular region dusky, branchiostegal membranes blackish posteriorly.

Material examined. 46 specimens. Holotype of Coelorhynchus hexafasciatus: BSKU 30443 (150 mm HL, 546+ mm TL), Kyushu-Palau Ridge, Japan, 26.7500ºN, 135.3167ºE, 336 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, sta. T8, bottom trawl, coll. Y. Kobayashi et al., 17 Dec. 1979 . Paratypes of C. hexafasciatus: BSKU 30440 (1, 62.6 mm HL, 213+ mm TL), BSKU 30441 (1, 73.9 mm HL, 274 mm TL) , BSKU 30442 (1, 73.9 mm HL, 275 mm TL), collected with holotype ; BSKU 29533 (1, 131 mm HL, 462+ mm TL), Kyushu-Palau Ridge, 26.7500ºN, 135.3167ºE, 336 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, tr. 9, bottom trawl, coll. O. Okamura et al., 17 Dec. 1979 ; BSKU 29427 (1, 97.6 mm HL, 334+ mm TL) , BSKU 29452 (1, 167 mm HL, 541+ mm TL), Kyushu-Palau Ridge, 27.9178ºN, 134.7460ºE, 685–710 m, F/ Vs Shinseimaru, No. 53 and Kyoyo-maru , No. 2, sta. 4-T8, bottom trawl, coll. O. Okamura et al., 19 Dec. 1978 ; BSKU 32149 (1, 131 mm HL, 460+ mm TL) , BSKU 32150 (1, 91.9 mm HL, 298+ mm TL) , BSKU 32151 (1, 73.6 mm HL, 253+ mm TL), Kyushu-Palau Ridge, 27.9178ºN, 134.7460ºE, 685–710 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, tr. T8, bottom trawl, coll. O. Okamura et al., 19 Dec. 1979 ; BSKU 29486 (1, 76.9 mm HL, 247+ mm TL) , BSKU 29506 (1, 115 mm HL, 418 mm TL), Kyushu-Palau Ridge, 27.9000ºN, 134.6667ºE, 697–700 m, F/ Vs Shinseimaru, No. 53 and Kyoyo-maru , No. 2, tr. 12, bottom trawl, coll. O. Okamura et al., 18 Dec. 1979 ; BSKU 30472 (1, 70.1 mm HL, 218+ mm TL) , BSKU 30473 (1, 75.3 mm HL, 233+ mm TL), Kyushu-Palau Ridge, 27.9000ºN, 134.6667ºE, 697–700 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, sta. T11, bottom trawl, coll. Y. Kobayashi et al., 18 Dec. 1979 ; BSKU 26106 (1, 90.3 mm HL, 291+ mm TL) , BSKU 26107 (1, 89.1 mm HL, 337 mm TL) , BSKU 26108 (1, 86.0 mm HL, 275+ mm TL) , BSKU 26109 (1, 85.7 mm HL, 313 mm TL) , BSKU 26110 (1, 88.3 mm HL, 298+ mm TL) , BSKU 26111 (1, 74.7 mm HL, 252+ mm TL), Kyushu-Palau Ridge, 27.9033ºN, 134.6583ºE, 700 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, sta. 2-4, bottom trawl, coll. Y. Kobayashi et al., 20 Feb. 1978 ; BSKU 26025 (1, 76.5 mm HL, 245+ mm TL) , BSKU 26026 (1, 74.8 mm HL, 255+ mm TL), Kyushu-Palau Ridge, 27.9000ºN, 134.6550ºE, 650 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, sta. 2-2, tr. 9, bottom trawl, coll. Y. Kobayashi et al., 15 Feb. 1978 ; BSKU 26070 (1, 118 mm HL, 416+ mm TL) , BSKU 26071 (1, 69.3 mm HL, 224+ mm TL) , BSKU 26072 (1, 96.4 mm HL, 335+ mm TL) , BSKU 26073 (1, 75.1 mm HL, 257+ mm TL) , BSKU 26074 (1, 70.6 mm HL, 256 mm TL) , BSKU 26075 (1, 74.0 mm HL, 258+ mm TL) , BSKU 26076 (1, 82.1 mm HL, 300 mm TL), Kyushu-Palau Ridge, 27.9167ºN, 134.6500ºE, 700 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, sta. 2- 3, bottom trawl, coll. Y. Kobayashi et al., 20 Feb. 1978 ; BSKU 30590 (1, 50.8 mm HL, 175+ mm TL) , BSKU 30591 (1, 79.6 mm HL, 263+ mm TL) , BSKU 30592 (1, 119 mm HL, 440 mm TL), Kyushu-Palau Ridge, 27.9000ºN, 134.6500ºE, 910 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru, No. 2, cr. Ky , sta. T-12, bottom trawl, coll. O. Okamura et al., 18 Dec. 1979 . Non-types : Japan : HUMZ 95116 (1, 156 mm HL), west of Amami-oshima, Okinawa Trough , 28.4033ºN, 127.7567ºE, 735–770 m, bottom trawl, coll. K. Amaoka, 9 Nov. 1981 ; BSKU 42885 (1, 122 mm HL, 416+ mm TL), Kyushu-Palau Ridge, F / Vs Shinsei-maru, No. 53 and Kyoyo-maru, No. 2, date unknown ; BSKU 40980 (1, 91.1 mm HL, 320+ mm TL) , BSKU 40981 (1, 53.5 mm HL, 181+ mm TL), Kyushu-Palau Ridge, 27.9100ºN, 134.6667ºE, 697–1320 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru , No. 2, bottom trawl, coll. O. Okamura et al., 18 Dec. 1979 ; HUMZ 71890 (1, 174 mm HL, 632+ mm TL) , HUMZ 71891 (1, 203 mm HL, 706+ mm TL) , HUMZ 71892 (1, 185 mm HL, 659+ mm TL) , HUMZ 71893 (1, 127 mm HL) , HUMZ 71897 (1, 108 mm HL), Shichito-Iojima Ridge , 26.1667ºN, 140.9167ºE, 500–1200 m, coll. Japan Marine Fishery Resources Research Center ( JAMARC), 30 Oct. 1977 ; NSMT-P 102809 (1, 137 mm HL, 533+ mm TL), NSMT-P 102810 (1, 86.9 mm HL, 325+ mm TL), off Hachijo-jima Island , Shichito-Iojima Ridge, F / V Ryoseimaru, 23 Apr. 2008 ; NSMT-P 64134 (1, 182 mm HL, 635+ mm TL), off Hachijo-jima Island , Shichito-Iojima Ridge, F / V Taiyo-maru, 6 Jun. 2001 ; FAKU 133888 (1, 93.5 mm HL, 354 mm TL), off Nii-jima Island , 20 Dec. 2010 . Taiwan: ASIZP 71202 (1, 133 mm HL, 494+ mm TL), Da-xi fish market, Yilan, 24.9400ºN, 121.9000ºE, coll. H.-C. Ho, 27 Mar. 2004 .

Counts and measurements. Based on 46 specimens (50.8–203 mm HL, 175+–706+ mm TL). Counts: first dorsal-fin rays II,8–10; pectoral-fin rays i16–i20; pelvic-fin rays 7; gill rakers on first arch (outer/inner) 0–3/7–11, on second arch 6–8/8–11; longitudinal scales 35–49; transverse scale rows below first dorsal-fin origin 6.5–9.5, below first dorsal-fin midbase 5–8, below second dorsal-fin origin 6– 10, above anal-fin origin 26–30; pyloric caeca 54.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 37–42 (57–70); orbit diameter 22–28 (35–45); postorbital length 34–41 (57–66); postrostral length 59–64; orbit–preopercle distance 37–47 (62–75); suborbital width 12–15 (20– 24); upper-jaw length 27–38 (45–61); length of rictus 21–31 (35–49); length of premaxillary tooth band 17–23 (27–37); preoral length 26–35 (41–58); length of lateral nasal ridge 20–33 (32–56); length of suborbital ridge 94–99 (147–163); snout width 23–28 (37–46); internasal width 17–21 (27–35); interorbital width 22–26 (35–43); occipital width 10 (15–16); body width over pectoral-fin bases 32–56 (53–88); body depth at first dorsal-fin origin 52–71 (85–112); body depth at anal-fin origin 40–60 (66– 95); prepelvic length 100–117 (162–188); preanus length 114–148 (186–233); preanal length 118–156 (193–248); isthmus–pelvic distance 27–38 (46–60); isthmus–anal distance 62–74 (98–116); pelvic–anal distance 33–69 (54–110); anus–anal distance 5–10 (8–17); pelvic-fin length 30–50 (48–82); pectoral-fin length 40–50 (66–80); predorsal length 103–112 (165–182); height of first dorsal fin 42–53 (69–88); length of first dorsal-fin base 15–25 (25–40); interdorsal length 13–24 (21–39); length of gill slit 15–20 (24–33); length of posterior nostril 7–17 (12– 28); barbel length 6–11 (10–18).

Size. Attains at least 71 cm TL (HUMZ 71891, 706+ mm TL, Shichito-Iojima Ridge, Japan).

Distribution. Known only from the Kyushu-Palau Ridge, Shichito-Iojima Ridge, and Okinawa Trough, at depths of 366–1320 m (Appendix 3-2D). Common at the Kyushu-Palau Ridge, but rare in other parts of its range.

Remarks. Coelorinchus hexafasciatus was described from 32 specimens collected from the Kyushu-Palau Ridge ( Figs. 40 C–D, 41). The reader can refer to the original description (Okamura 1982) for further morphological details. Recently, Iwamoto et al. (2015) reported an additional specimen from the Da-xi fish market in northern Taiwan. This species was also obtained from the middle Okinawa Trough and the Shichito-Iojima Ridge (see Nakayama et al. 2015c:258).

Relationships. Coelorinchus hexafasciatus belongs to the C. tokiensis group as redefined by Nakayama et al. (2015c). In addition to C. hexafasciatus , this group includes the following five species: C. celaenostoma McMillan & Paulin, 1993 and C. osipullus McMillan & Iwamoto, 2009 from New Caledonia to New Zealand; C. quadricristatus (Alcock in Wood-Mason & Alcock, 1891) from the Andaman Sea; C. sheni Chiou, Shao & Iwamoto, 2004 from Japan and Taiwan; and C. tokiensis (Steindachner & D̂derlein, 1887) from Japan and the South China Sea. The above six species are separable from other congeners by having the following combination of features (modified from Nakayama et al. 2015c): light organ externally represented by short naked streak anterior to anus, its anterior margin falling far short of line connecting inner pelvic-fin bases; dorsal profile of snout almost straight in lateral view; lateral nasal ridge incompletely supported by nasal bone; premaxillary teeth in long tapered band, with outer series enlarged; posterior end of premaxillary tooth band almost reaching lateral corner of mouth; body scales covered with keel-like spinules in widely divergent, saw-toothed ridges; series of dark saddles on body; and oral cavity blackish.

Comparisons. Coelorinchus hexafasciatus differs most notably from other species of the C. tokiensis group except C. tokiensis in having the underside of the head completely naked except oval scaly parches on the ventral surfaces of the preopercles. The species is further distinguished from C. celaenostoma by having a shorter snout (57–70% PRL vs. 86–94%; preoral length 41–58% PRL vs. 71–80%), about 6–7 dark saddles on the body (vs. ca. 5), pale lips (vs. black), and lacking a bluish band completely encircling the trunk (vs. present); from C. osipullus by having a shorter barbel (10–18% PRL vs. 19–26%) and fewer saddles on the body (ca. 6–7 vs. ca. 9–11); and from C. quadricristatus and C. sheni by having a bluntly pointed tip of the snout (vs. sharply pointed). Coelorinchus hexafasciatus is most similar to the sympatric C. tokiensis , but differs in having a shorter snout (57–70% PRL vs. 70–85%) with negative allometry (vs. positive; Nakayama et al. 2015c).

Figures

FIGURE 40. Fresh specimens of Coelorinchus hexafasciatus. (A) FAKU 133888, 93.5 mm HL, 354 mm TL, Tokyo Bay, Pacific; (B) HUMZ 71893, 127 mm HL, 416+ mm TL, Shichito-Iojima Ridge, Pacific, 500–1200 m depth; (C) BSKU 29533, paratype, 131 mm HL, 462+ mm TL, Kyushu-Palau Ridge, Pacific, 336 m depth; (D) BSKU unknown, Kyushu-Palau Ridge. Lateral views. [Photos: (A) Y. Kai; (B) HUMZ; (C–D) BSKU]

FIGURE 41. Holotype of Coelorhynchus hexafasciatus (= Coelorinchus hexafasciatus). BSKU 30443, 150 mm HL, 546+ mm TL, Kyushu-Palau Ridge, Pacific, 336 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 42. Scanning electron micrographs showing body scales (from the dorsum below the interdorsal space) of three species of the Coelorinchus tokiensis group. (A–B) C. hexafasciatus, BSKU 29452, paratype, 167 mm HL; (C–D) C. sheni, CAS 215541, 112 mm HL; (E–F) C. tokiensis, BSKU 26104, paratype of C. longicephalus, 202 mm HL. (A, C, E) Views from above; (B, D, F) oblique views. [Photos: (A–B, E–F) N. Nakayama; (C–D) NSMT]