Coelorinchus divergens Okamura & Yatou, 1984

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 45-48

Coelorinchus divergens Okamura & Yatou, 1984

[Japanese name: Hanare-hige]

( Figs. 30 , 31 A–B; Appendix 3-1F)

Coelorinchus divergens Okamura & Yatou, 1984:237 , fig. 169 (original description; holotype: BSKU 26865, from Okinawa Trough; 1 paratype from Okinawa Trough; new Japanese name: “Hanare-hige”); Okamura 1988:453, pl. 373, fig. J (compiled); Shao et al. 2008b: table 2 (15 spec. listed from northeastern and southwestern Taiwan, and South China Sea); Nakabo & Kai 2013:509 (in key; Japan); Iwamoto et al. 2015:53, fig. 5 (brief description; 17 spec. from northeastern and eastern Taiwan, South China Sea, and Philippines); Motomura 2020:38 (listed; Japan).

Caelorinchus divergens: Nakabo 1993:368 (in key; Japan); Nakabo 2000:432 (in key; Japan); Nakabo 2002:432 (in key; Japan); Yoda et al. 2002:11 (listed; East China and Yellow Seas); Shinohara et al. 2005:416 (listed; Ryukyu Islands).

Diagnosis. No external evidence of light organ anterior to anus. Underside of head, including ventral surfaces of preopercles, and dorsal surface of snout almost completely and uniformly scaled; nasal fossa scaled anteroventrally. Snout long, sharply pointed, length 64–69% PRL; dorsal profile of snout almost straight in lateral view; terminal scute moderately short, diamond-shaped, dorsoventrally flattened; lateral nasal ridge incompletely supported by nasal bone. Anus abutting anal-fin origin. Premaxillary teeth small, conical, arranged in short, uniformly wide band, with outer series slightly enlarged; posterior margin of tooth band falling far short of lateral corner of mouth. Body scales covered with stout, narrowly trihedral, shieldlike spinules in subparallel ridge-like rows; middle row enlarged and higher, giving striated appearance to body surface; lateral rows often incomplete, not extending to posterior scale margin; buttresses broadly developed. Transverse scale rows below first dorsal-fin origin 5.5–6. Occipital scales covered with widely divergent, crest-like rows of keel-like spinules; no prominent naked area atop head between parietal ridges. Modified scales on head ridges prominently spiny and thickened. Free neuromasts on underside of head not especially enlarged. Upperjaw length 45–47% PRL; height of first dorsal fin 58– 74% PRL. Head and body uniformly dark brown; orbit narrowly edged in black; all fins blackish.

Material examined. 3 specimens. Holotype of Coelorinchus divergens: BSKU 26865 (98.1 mm HL, 358+ mm TL), north-northwest of Amami-oshima Island , Kagoshima Pref., Okinawa Trough , Japan, East China Sea, 29.7850ºN, 128.4467ºE, 1000 m, F/ V Yuryo-maru, No. 8, tr. 17, bottom trawl, coll. Y. Kinoshita and S. Hagino, 3 Feb. 1978 . Paratype of C. divergens: BSKU 33464 (1, 81.6 mm HL, 315+ mm TL), west of Yaku-shima Island , Okinawa Trough, 30.2067ºN, 128.2833ºE, 780–810 m, F/ V Yuryo-maru, No. 8, sta. 3, tr. T1, bottom trawl, coll. H. Maeda, 26 Oct. 1979 . Non-type : South China Sea: ASIZP 66084 (1, 73.7 mm HL, 214+ mm TL), 20.7167ºN, 117.5500ºE, 954 m, otter trawl, coll. P.-F. Lee, 19 Aug. 2005 .

Counts and measurements. Based on 3 specimens (73.7–98.1 mm HL, 214+–358+ mm TL). Counts: first dorsal-fin rays II,7–8; pectoral-fin rays i17–i18; pelvicfin rays 7; gill rakers on first arch (outer/inner) 0/7–9, on second arch 6/8–9; longitudinal scales 28–42; transverse scale rows below first dorsal-fin origin 5.5–6, below first dorsal-fin midbase 4–5.5, below second dorsal-fin origin 5–5.5.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 39–41 (64–69); orbit diameter 25–27 (41–44); postorbital length 34–36 (56–59); postrostral length 60–62; orbit–preopercle distance 35–37 (56–61); suborbital width 14–15 (22–25); upper-jaw length 28–28 (45–47); length of rictus 21–22 (34–37); length of premaxillary tooth band 12–15 (20– 24); preoral length 32–36 (52–60); length of terminal snout scute 7 (12); length of lateral nasal ridge 26–29 (42–48); length of suborbital ridge 91–97 (148–162); snout width 26–31 (43–52); internasal width 20–22 (32– 35); interorbital width 24–26 (40–42); occipital width 8 (14); body width over pectoral-fin bases 37–46 (62–75); body depth at first dorsal-fin origin 48 (80); body depth at anal-fin origin 37 (63); prepelvic length 103–109 (168– 183); preanus length 140 (234); preanal length 143 (239); isthmus–pelvic distance 26–32 (44–52); isthmus–anal distance 63 (105); pelvic–anal distance 38 (63); pelvicfin length 34–43 (56–70); pectoral-fin length 35–42 (58– 67); predorsal length 107–112 (177–181); height of first dorsal fin 35–46 (58–74); length of first dorsal-fin base 13–15 (22–24); interdorsal length 13–14 (22–23); length of gill slit 12–14 (20–22); length of posterior nostril 7–9 (12–15); barbel length 7–9 (11–15).

Size. To about 36 cm TL ( BSKU 26865 , holotype, 358+ mm TL).

Distribution. Restricted to Japan and Taiwan. So far known only from the Okinawa Trough and northern South China Sea at depths of 515–1110 m ( Shao et al. 2008a, 2008b; this study; Appendix 3-1F). Very rare.

Remarks. Coelorinchus divergens was described from two specimens collected from the Okinawa Trough ( Fig. 30 ), and subsequently recorded from the East and South China Seas off Taiwan ( Shao et al. 2008a, 2008b; Iwamoto et al. 2015). For further morphological details see the original description given by Okamura & Yatou (1984). Despite intensive collecting efforts, no additional specimens have been collected from Japanese waters.

Relationships. Coelorinchus divergens falls into a group of Coelorinchus species characterized by the following combination of features: no external evidence of light organ anterior to anus; lateral nasal ridge incompletely supported by nasal bone; premaxillary teeth in short, uniformly wide band; underside of head entirely or almost entirely scaled; body scales covered with shield-like spinules in parallel to subparallel rows, with middle row enlarged and some rows incomplete; buttresses of body-scale spinules broadly developed; modified scales on head ridges prominently spiny and thickened; body uniformly dark brown to swarthy. This group was originally recognized by Iwamoto et al. (2006:437), and is called here the C. parallelus group. Apart from C. divergens , nine valid species belong to this group: C. acanthiger Barnard, 1925 from southern Africa across the Indian Ocean to Australia and New Zealand; C. amirantensis Iwamoto, Golani, Baranes & Goren, 2006 from the Seychelles and the Mascarene Ridge in the Indian Ocean; C. braueri Barnard, 1925 from South Africa; C. kermadecus Jordan & Gilbert in Jordan & Starks, 1904 from the southwestern Pacific; C. mycterismus McMillan & Paulin, 1993 from New Zealand and off the Pacific and Indian Ocean coasts of Australia; C. parallelus (G̹nther, 1877) from Japan, Taiwan, and New Caledonia (a senior synonym of C. sparsilepis Okamura & Yatou, 1984 ; see the Nomenclatural discussion of C. parallelus ); C. spinifer Gilbert & Hubbs, 1920 from the Gulf of Tomini, Indonesia, and the South China Sea off Taiwan; C. trachycarus Iwamoto, McMillan & Shcherbachev, 1999 from the southwestern Pacific and off the southern and western coasts of Australia; and C. yurii Iwamoto, Golani, Baranes & Goren, 2006 from the Seychelles and the Mascarene Ridge in the Indian Ocean.

Comparisons. Coelorinchus divergens readily differs from C. acanthiger in having fewer scales below the first dorsal-fin origin (5.5–6 vs. 7–10) and in lacking a prominent naked area atop the head between the parietal ridges; from C. amirantensis and C. yurii in that the underside of the head is densely scaled (vs. somewhat sparsely scaled); from C. braueri and C. yurii in having a lower first dorsal fin (height of first dorsal fin 58–74% PRL vs.>98%); from C. mycterismus in that the dorsal contour of the snout is almost straight (vs. distinctly concave); and from C. trachycarus in that the ventral surfaces of preopercles are heavily scaled (vs. broadly naked). Coelorinchus divergens also differs from all except C. kermadecus , C. mycterismu s, C. parallelus , and C. spinifer in that the nasal fossa is heavily scaled (vs. completely or generally naked); all except C. acanthiger , C. braueri , C. parallelus , and C. yurii in having a distinctly shorter snout (64–69% PRL vs.>74%); and from all except C. kermadecus and C. parallelus in having a somewhat larger mouth (upper-jaw length 45–47% PRL vs. <45%).

Coelorinchus divergens may be confused with C. parallelus , with which it occurs sympatrically in the East and South China Seas. However, these two species are readily distinguished by two squamation characters. The first character concerns spinulation of the occipital scales, and C. divergens readily differs from C. parallelus in having occipital scales covered with divergent rows of spinules (vs. uniserial). The second character involves the shape and arrangement of the body-scale spinules; although both species have prominent buttresses at each base of the spinules, those of C. divergens are less developed than those of C. parallelus ( Fig. 31 A–B vs. C–F); consequently, the spinules of C. divergens are narrowly triangular in appearance, whereas those of C. parallelu s are broadly triangular. Coelorinchus divergens further differs from C. parallelus by having a relatively larger mouth (upper-jaw length 45–47% PRL vs. 36–46%) and a shorter snout (64–69% PRL vs. 67–89%), although these ranges are slightly overlapping.

Figures

FIGURE 30. Holotype of Coelorinchus divergens. BSKU 26865, 98.1 mm HL, 358+ mm TL, Okinawa Trough, East China Sea, 1000 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 31. Scanning electron micrographs showing body scales (from the dorsum below the interdorsal space) of two species of the Coelorinchus occa group.(A–B) C. divergens, BSKU33464, paratype, 81.6 mm HL; (C–D) C. parallelus, BMNH 1887.12.7.65, lectotype, 93.2 mm HL; (E–F) C. parallelus, BSKU 28441, holotype of C. sparsilepis, 73.3 mm HL. (A, C, E) Views from above; (B, D, F) oblique views. [Photos: (A–B, E–F) NSMT; (C–D) N. Nakayama]