Coelorinchus brevirostris Okamura, 1984

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 38-42

Coelorinchus brevirostris Okamura, 1984

[Japanese name: Tsumari-hige]

( Figs. 26–27 , 28 A–B; Appendix 3-1D)

Coelorinchus brevirostris Okamura, 1984a:225 , fig. 160 (original description; holotype: BSKU 29562, from Okinawa Trough, 25º47.4ʹN, 124º23.4ʹE, in 600 m; new Japanese name: “Tsumari-hige”); Okamura 1988:453, pl. 373, fig. G (compiled); Okamura 1997:126, fig. 4 (compiled); Shao et al. 2008b: table 2 (6 spec. listed from northeastern and eastern Taiwan and South China Sea); Nakabo & Kai 2013:507 (in key; Japan); Iwamoto et al. 2015:51 (brief description; 21 spec. from northeastern and eastern Taiwan and South China Sea); Motomura 2020:38 (listed; Japan).

Caelorinchus brevirostris: Nakabo 1993:367 (in key; Japan); Nakabo 2000:431 (in key; Japan); Nakabo 2002:431 (in key; Japan); Yoda et al. 2002:11 (listed; East China and Yellow Seas); Chiou et al. 2004b:301, figs. 4–5 (redescription; 11 spec. from Da-xi; first record from Taiwan); Shinohara et al. 2005:416 (listed; Ryukyu Islands); Furuhashi et al. 2010: table 2 (1 spec. listed from northern Okinawa Trough).

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.Snout long, sharply pointed, length 67–83% PRL; dorsal profile of snout straight in lateral view; terminal scute short, moderately broad, arrowhead-shaped, dorsoventrally flattened, length 14–17% PRL; distal portion of snout broadly spade-shaped when viewed dorsally; lateral nasal ridge incompletely supported by nasal bone. Interdorsal space shorter than first dorsal-fin base length.Anal fin originating posterior to vertical through second dorsal-fin origin. Second spinous ray of first dorsal fin greatly elongate, height of fin 139– 220% 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, none especially 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 overlapping, but free from one another, with last spinule extending well beyond posterior scale margin; buttresses narrowly developed. Spinules on scales anterior to light organ rudimentary. Orbit diameter 43–47% PRL; postorbital length 52–56% PRL; upper-jaw length 36–38% PRL; preoral length 58–72% PRL; barbel length 4–10% PRL. Transverse scale rows below first dorsal-fin midbase 3.5–5.5. Body pale overall, lacking prominent blotches or saddles; scale pockets gently outlined by dark brown; underside of head dusky, heavily peppered; lips pale; oral cavity blackish; gular membrane almost immaculate, but branchiostegal membranes moderately dark; first dorsal fin blackish; pelvic fin dark, but outermost ray paler distally.

Material examined. 7 specimens. Holotype of Coelorinchus brevirostris: BSKU 29562 (54.2 mm HL, 204+ mm TL), northwest of Miyako-jima Island , Okinawa Pref., Okinawa Trough , Japan , East China Sea , 25.7900ºN, 124.3900ºE, 600 m, F/ V Yuryo-maru, No. 8, sta. 1-T13, bottom trawl, coll. T. Kitajima, 20 Sept. 1979. Non-types: Japan: FFNU P-00640 (2, 52.0– 52.6 mm HL, 212+– 224 mm TL), east of Okihirazi Bank , East China Sea , 32.1757ºN, 129.4868ºE, 476 m, T/ V Nagasakimaru, cr. N218, sta. B5-4, 3-m ORE beam trawl, coll. J. Hashimoto, 1 Aug. 2006; FAKU 84522 (1, 52.6 mm HL, 221+ mm TL), west of Yaku-shima Island , Okinawa Trough , 30.4133ºN, 128.2300ºE, 499–500 m, FRV Yokomaru , sta. D9, tr. T-2, 10 Nov. 2002. Taiwan: ASIZP 61352 (1, 36.2 mm HL, 147+ mm TL), Da-xi fish market, Yilan, bottom trawl, 1 Jun. 2001; ASIZP 61350 (1, 53.1 mm HL, 181+ mm TL), Da-xi fish market, Yilan, bottom trawl, 30 Jun. 2000. South China Sea: ASIZP 66806 (1, 47.1 mm HL, 181+ mm TL), northeast of Dong-sha Atoll, 21.6701ºN, 117.7195ºE, 509 m, beam trawl, coll. H.-M. Yeh et al., 17 Aug. 2005.

Counts and measurements. Based on 7 specimens (36.2–54.2 mm HL, 147+– 224 mm TL). Counts: first dorsal-fin rays II,7–9; pectoral-fin rays i15–i19; pelvicfin rays 7; gill rakers on first arch (outer/inner) 0/6–8, on second arch 5/7–8; longitudinal scales 29–32; transverse scale rows below first dorsal-fin origin 4.5–6.5, below first dorsal-fin midbase 3.5–5.5, below second dorsal-fin origin 4.5–6.5, above anal-fin origin 15.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 41–46 (67–83); orbit diameter 24–27 (43–47); postorbital length 30–33 (52–56); postrostral length 56– 61; orbit–preopercle distance 28–33 (50–55); suborbital width 12–14 (21–26); upper-jaw length 20–22 (36–38); length of rictus 15–16 (26–29); length of premaxillary tooth band 6–9 (11–15); preoral length 35–40 (58–72); length of terminal snout scute 8–10 (14–17); length of lateral nasal ridge 28–30 (48–54); length of suborbital ridge 90–92 (148–165); snout width 29–32 (50–55); internasal width 19–20 (31–35); interorbital width 19–21 (32–36); occipital width 9–10 (14–17); body width over pectoral-fin bases 39–46 (68–81); body depth at first dorsal-fin origin 43–49 (75–83); body depth at anal-fin origin 38–43 (66–77); prepelvic length 113–125 (193– 224); preanus length 158 (270); preanal length 162–164 (279–291); isthmus–pelvic distance 25–29 (43–51); isthmus–anus distance 74 (126); isthmus–anal distance 66–79 (114–135); pelvic–anal distance 42–53 (73–90); anus–anal distance 6 (10); pelvic-fin length 37–44 (64– 75); pectoral-fin length 40–44 (67–74); predorsal length 104–112 (180–190); height of first dorsal fin 82–125 (139–220); length of first dorsal-fin base 16–20 (27–34); interdorsal length 10–16 (18–28); length of gill slit 12–13 (20–22); length of posterior nostril 6–10 (10–17); barbel length 3–6 (4–10).

Supplementary description based on Japanese specimens. Coelorinchus brevirostris has been well described by Okamura (1984a) and Chiou et al. (2004b) that can be referred to for details. Three additional specimens collected from the northern Okinawa Trough ( FAKU 84522 1, 52.6 mm HL, 221+ mm TL; FFNU P-640, 2, 52.0– 52.6 mm HL, 212+– 224 mm TL) allowed to document previously unknown features regarding squamation. General features of the species are shown in Figs. 26–27 .

Body scales moderate in size, thin, highly deciduous, covered with short, reclined, needle-like spinules in subparallel to slightly divergent rows ( Fig. 28A ); those on dorsum below interdorsal space with about 6 rows of spinules; every spinule row complete, extending to posterior scale margin; middle row not especially high or enlarged; spinules in each row greatly overlapping, but free from one another; height of spinules gradually increasing posteriorly, with tips of last spinules extending well beyond posterior scale margin; lateral buttresses narrowly developed; no reticulate structures on unexposed potion. Spinules on chest scales anterior to light organ rudimentary ( Fig. 28B ).

Size. To about 22 cm TL ( FFNU P-640, 1 of 2, 224 mm TL, Okinawa Trough , Japan) .

Distribution. Known only from the Okinawa Trough, Taiwan Strait, and northern South China Sea, at depths of 455–1185 m ( Chiou et al. 2004b; Shao et al. 2008a, 2008b; this study; Appendix 3-1D). Very rare in Japanese waters.

Remarks. Coelorinchus brevirostris was originally described from a single specimen collected from the Okinawa Trough, southern Japan, in 600 m. The holotype ( Fig. 27 ) is in a somewhat poor condition, with all body scales missing and the tip of the first dorsal fin broken. Chiou et al. (2004b) redescribed the species based on 11 specimens obtained at the Da-xi fish market in northeastern Taiwan, and newly documented that the second spinous ray of the first dorsal fin is greatly elongated. Subsequently, Furuhashi et al. (2010) reported two Japanese specimens (FFNU P-00640) collected from the Okinawa Trough off Nagasaki Pref., which represents the northernmost record for the species. An additional specimen from the west of Yaku-shima Island in the Okinawa Trough was also found among the fish collection of the Kyoto University Museum ( Fig. 26 ).

Relationships. Coelorinchus brevirostris falls in the group of Coelorinchus species as defined by Iwamoto et al. (2009:43–44) to include the following 10 species (this group is called here the C. hubbsi group; see also Nakayama et al. 2020): C. brevirostris , C. cingulatus Gilbert & Hubbs, 1920 from Japan to the South China Sea (see also the Remarks of that species); C. cylindricus Iwamoto & Merrett, 1997 from the Norfolk Ridge and New Zealand; C. gladius Gilbert & Cramer, 1897 from Hawaii; C. fuscigulus Iwamoto, Ho & Shao, 2009 from Japan to Taiwan; C. hubbsi Matsubara, 1936 from Japan to Taiwan; C. matsubarai Okamura, 1982 from the Kyushu-Palau Ridge and the Emperor Seamounts; C. melanosagmatus Iwamoto & Anderson, 1999 from the Indian Ocean; C. multifasciatus Sazonov & Iwamoto, 1992 from the Sala y Gomez Ridge; and C. spilonotus Sazonov & Iwamoto, 1992 from the Nazca and Sala y Gomez Ridges and Hawaii. These species are distinctive within the genus in having a somewhat cylindrical body, a long light organ with two external fossae (of which one is immediately anterior to the anus and the other is on the chest immediately posterior to the isthmus), a welldeveloped second dorsal fin (as high as the anal fin), a narrow interdorsal space (less than the first dorsal-fin base length), an incomplete bony support for the lateral nasal ridge, the absence of scales on the underside of the head except for overlapping scales along the lateral nasal ridges (small scaly patches occasionally found above the posterior margins of the upper jaw), and body scales covered with needle-like spinules in subparallel to slightly divergent rows.

Coelorinchus acutirostris Smith & Radcliffe in Radcliffe, 1912 distributed in the Philippines, Australia, and New Caledonia agrees generally with the above-mentioned features, but its lateral nasal ridge is completely supported by the nasal bone. It further differs from all species of the C. hubbsi group in having body scales covered in widely divergent rows of erect spinules (vs. subparallel to slightly divergent rows of reclined spinules).

Coelorinchus melanobranchus Iwamoto & Merrett, 1997 , known from New Caledonia, is also similar in many aspects to the members of the C. hubbsi group. However, it has very different physiognomy associated with a bluntly pointed snout (47–57% PRL vs. Ż60%), a short terminal scute (4–8% PRL vs. Ż12%), a narrow interorbital space (27–32% PRL vs. Ż32), and a long chin barbel (33–42% PRL vs. ±19%).

This group almost corresponds with Okamura’s (1984a:227) “ hubbsi complex”, although the latter also includes C. acutirostris .

Comparisons. Coelorinchus brevirostris differs most notably from all other species of the C. hubbsi group in lacking prominent body markings on the body (vs. dark saddles, blotches, or stripes present) and in having rudimentary spinules on the chest scales anterior to the anterior fossa of the light organ (vs. generally similar to those on the dorsum). It also differs from all except C. cingulatus by having a greatly elongate second spinous ray of the first dorsal fin (vs. not elongate). Coelorinchus brevirostris further differs from C. cingulatus in having shorter terminal scute (14–17% PRL vs. 20–26%) and chin barbel (4–10% PRL vs. 10–13%), and prominent naked clefts along each side of the median rostral ridge (vs. only narrowly developed). The shape of the snout is also significantly different between the two species. In C. brevirostris , its dorsal contour is almost straight in lateral view, whereas it is obviously concave in C. cingulatus . When viewed dorsally, the anterolateral margins are broadly convex in C. brevirostris , giving a spade-shaped appearance to the snout. In contrast, C. cingulatus has a more attenuated snout in dorsal view, with the leading edges distinctly concave anteriorly.

Figures

FIGURE 26. Fresh specimen of Coelorinchus brevirostris. FAKU 84522, 52.7 mm HL, 221+ mm TL, west of Yaku-shima Island, Okinawa Trough, East China Sea, 499–500 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. [Photos: Kyoto University Museum]

FIGURE 27. Holotype of Coelorinchus brevirostris. BSKU 29562, 54.2 mm HL, 204+ mm TL, Okinawa Trough, East China Sea, 600 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

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]