Coelorinchus nox, Nakayama, Naohide, 2020

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 113-118

Coelorinchus nox sp. nov.

[New Japanese name: Yami-hige]

( Figs. 75–77 , 78A ; Table 3 ; Appendix 3-4E)

Diagnosis. Light organ externally represented by short, narrow, naked fossa immediately anterior to anus, its anterior margin falling far short of line connecting inner pelvic-fin bases. Underside of head mostly scaled except for narrow to moderately broad naked area above upper lip, and anterior portions of mandibular rami; dorsal surfaces of snout fully scaled. Snout long, sharply pointed, length 62–81% PRL; dorsal profile of snout slightly concave in lateral view; terminal scute moderately short, diamondshaped, dorsoventrally flattened, length 12–17% PRL; lateral nasal ridge completely supported by nasal bone, moderately convex in dorsal view, giving spade-shaped appearance to snout. Anus slightly separated from analfin origin. Premaxillary teeth small, conical, arranged in short, uniformly wide band, none distinctly enlarged (outer series slightly larger); posterior margin of tooth band falling far short of lateral corner of mouth. Body scales covered with short, reclined, keel-like spinules in widely divergent, coarsely saw-tooth ridges; every spinule row complete, extending to posterior scale margin; spinules in each row greatly overlapping, increasing in height posteriorly; buttresses narrowly developed. Occipital scales covered with short, erect, needle-like spinules in 4 or more widely divergent, comb-like rows. Orbit diameter 45–52% PRL; suborbital width 18–23% PRL; internasal width 27–31% PRL; interorbital width 39–41% PRL; pectoral-fin length 57–69% PRL; pectoral-fin rays i16– i17; transverse scale rows below first dorsal-fin midbase 3.5–4.5. Body uniformly dark brown, without either dark saddles or blotches; lips pale to dusky; oral cavity blackish; gular and branchiostegal membranes heavily peppered with small melanophores; first dorsal, pectoral, and pelvic fins uniformly blackish.

Material examined. 14 specimens. Holotype: BSKU 109205 (99.2 mm HL, 346+ mm TL), west of Amami-oshima Island, Okinawa Trough , 28.5679ºN, 127.0421ºE, 607 m, T/ V Nagasaki-maru, cr. N365, sta. J6, tr. 1, 3-m ORE beam trawl, coll. N. Nakayama, 16 Nov. 2012 . Paratypes: BSKU 26321 (1, 90.6 mm HL, 313+ mm TL) , BSKU 26322 (1, 127 mm HL, 437+ mm TL) , BSKU 26323 (1, 98.3 mm HL, 339+ mm TL), off Senkaku Islands, Okinawa Trough , 25.6283ºN, 122.8933ºE, 560–692 m, F/ V Yuryo-maru, No. 8, tr. 3, bottom trawl, coll. T. Kitajima et al., 14 Jan. 1978 ; BSKU 28498 (1, 99.9 mm HL, 338+ mm TL) , BSKU 28499 (1, 105 mm HL, 335+ mm TL), northwest of Amami-oshima Island, Okinawa Trough , 29.7333ºN, 128.0500ºE, 815 m, F/ V Ryoan-maru, No. 28, tr. 74, bottom trawl, coll. Y. Kinoshita and S. Hagino, 20 Mar. 1978 ; BSKU 27985 (1, 116 mm HL, 354+ mm TL) , BSKU 27988 (1, 111 mm HL, 379+ mm TL), northwest of Amami-oshima Island, Okinawa Trough , 28.8333ºN, 127.2333ºE, 700–740 m, F/ V Ryoan-maru, No. 28, tr. 59, bottom trawl, coll. Y. Kinoshita and S. Hagino, 16 Mar. 1978 ; BSKU 27582 (1, 91.7 mm HL, 293+ mm TL), northwest of Amami-oshima Island, Okinawa Trough , 28.7167ºN, 127.2333ºE, 750– 755 m, F/ V Ryoan-maru, No. 28, tr. 48, bottom trawl, coll. Y. Kinoshita and S. Hagino, 11 Mar. 1978 ; BSKU 109016 (1, 79.8 mm HL, 271+ mm TL), west of Amami-oshima Island, Okinawa Trough , 28.5686ºN, 127.0419ºE, 604 m, T/ V Nagasaki-maru, cr. N365, sta. J6, tr. 4, 3-m ORE beam trawl, coll. N. Nakayama, 16 Nov. 2012 ; BSKU 109011 (1, 87.3 mm HL, 297+ mm TL), west of Amamioshima Island, Okinawa Trough , 28.5513ºN, 127.0375ºE, 621 m, T/ V Nagasaki-maru, cr. N365, sta. J6, tr. 3, 3- m ORE beam trawl, coll. N. Nakayama, 16 Nov. 2012 ; BSKU 109206 (1, 81.8 mm HL, 270+ mm TL), collected with holotype ; BSKU 27673 (1, 112 mm HL, 375+ mm TL) , BSKU 27675 (1, 111 mm HL, 378+ mm TL), west of Okinawa-jima Island, Okinawa Trough , 28.7333ºN, 127.0167ºE, 610–640 m, F/ V Ryoan-maru, No. 28, tr. 49, bottom trawl, coll. Y. Kinoshita and S. Hagino, 11 Mar. 1978 .

Description. General features are shown in Figs. 75– 76 . Counts and measurements are given in Table 3 . Body deepest at first dorsal-fin origin, progressively tapering to long, laterally compressed tail. Trunk short, moderately compressed, width over pectoral-fin bases 1.1–1.3 in depth below first dorsal-fin origin. Head large, HL about 3.1–3.5 in TL. Snout long, sharply pointed, protruding well beyond upper jaw, length 1.2–1.8 times as long as orbit diameter; dorsal contour of snout slightly concave in lateral view; lateral nasal ridge completely supported by nasal bone; anterolateral margins of snout moderately convex when viewed dorsally, giving spade-shaped appearance to snout. Orbit large, its greatest diameter 0.9–1.2 in postorbital length. Interorbital space broad, flat, width 1.1–1.3 in orbit diameter. Mouth moderately large, inferior, protrusible, upper-jaw length 0.9–1.3 in orbit diameter; posterior margin of maxilla extending beyond vertical through midorbit; lateral corner of mouth barely restricted by skin folds; lips thin, slightly papillose near tooth bands. Suborbital region divided by longitudinal bony ridge passing from tip of snout to posteroventral angle of opercle; its upper half almost vertical, lower half sharply inclined mesially. Preopercle large, posterior margin inclined, forming moderately angular lobe at posteroventral corner. Subopercle prolonged ventrally as slender flap; posterior margin deeply concave. Gill membranes broadly connected across, and attached mesially to isthmus, with free posterior fold. Outer gill slit moderately restricted by skin folds, length 2.0– 2.5 in orbit diameter. Gill rakers small, low, tubercular, armed with short, fine spines; no rakers on outer side of first arch and inner side of fourth arch; gill filaments moderately long. Chin barbel short, slender, length 2.3–3.6 in orbit diameter.

Anus only slightly separated from anal-fin origin by 1–2 scale rows. Light organ externally represented by short, narrow, naked streak anterior to anus; its anterior margin not extending to about posterior 1/3 of distance from outer pelvic-fin bases to anus, and falling far short of line connecting inner pelvic-fin bases.

Teeth small, sharp, conical, gently incurved, in narrow bands in both jaws. Premaxillary teeth in short, uniformly wide band, with about 5 tooth rows near symphysis; posterior margin of tooth band falling far short of lateral corner of mouth; teeth becoming progressively smaller inwardly, with outer series only slightly larger. Mandibular teeth uniformly small, in narrow tapered band, with about 4 tooth rows across widest point near symphysis; posterior margin of tooth band extending beyond lateral corner of mouth. All teeth deeply embedded in thick layer of gum papillae.

Scales on body large, thin, moderately deciduous, covered with short, reclined, keel-like spinules in widely divergent rows ( Fig. 77 ); in 86.6 mm HL specimen (BSKU 109011), those on dorsum below interdorsal space with 6–8 rows of spinules; middle row usually longest with about 8 spinules, but not especially high or enlarged compared with adjacent rows; every spinule row complete throughout; spinules forming angle of about 40º to scale surface; spinules greatly overlapping, closely adjoined to one another, but their distal tips usually free, forming saw-toothed ridges that give spiny appearance to body surfaces; height of spinules increasing posteriorly, with tip of last in each row extending moderately beyond posterior scale margin; buttresses of spinules narrowly developed; no reticulate structures on unexposed potion. Body fully scaled except for fins and ventral light organ.

Scales on head ridges thickened and coarsely modified; those on median rostral ridge covered with radiating rows of spinules.Terminal snout scute moderately short, diamond-shaped, dorsoventrally flattened, its length 2.7–4.3 in orbit diameter. Supraoccipital scute stout, prominent, armed with single row of spinules; posttemporal scutes present, but not especially marked. Occipital scales covered with short, erect, needle-like spinules in widely divergent rows ( Fig. 78A ); spinules in each row free from one another, forming comb-like ridges, and their height gradually increasing posteriorly; scales on dorsal surfaces of snout posterior to leading edges armed with divergent rows or small cluster of short, erect, needle-like spinules. Other scales on head variable in size, generally similar to those on body, but spinules more erect; those on opercle, preopercle, and postorbital and supratemporal canals largest. Nasal fossa and dorsal surfaces of snout fully scaled; naked clefts along each side of median rostral ridge rudimentary. Underside of head completely scaled, except for narrow to moderately broad area above upper lip, anterior portions of mandibular rami, and posteroventral margins of preopercles; scales on ventral surfaces of head small, non-imbricate, covered with small cluster of short, erect, needle-like spinules.

No open pores along cephalic sensory canals. Free neuromasts scattered over head surfaces, especially on underside of snout, but not prominently marked. Anterior nostril small and circular; posterior large, bean-shaped; septum between nostrils forming anteriorly opened hood. Lateral line complete, not interrupted throughout.

Origins of first dorsal and pelvic fins on about same vertical; first dorsal fin moderately high, its height 2.1–3.0 times as long as its base length; second spinous ray not elongated, smooth along its leading edge; its tip usually extending to second dorsal-fin origin or beyond when laid back. Interdorsal space 1.4–2.2 times as long as first dorsal-fin base length. Second dorsal fin originating posterior to anal-fin origin (above bases of 2nd–7th analfin rays). Pectoral fin inserted slightly anterior to vertical through pelvic-fin base. Outer pelvic-fin ray prolonged, with fine distal tip.

Color when fresh ( Fig. 75 ). Head and body uniformly dark brown; gill cover slightly iridescent; all fins blackish.

Color in alcohol ( Fig. 76 ). Head and body uniformly dark brown; abdomen dark blue; lips pale to dusky; oral and gill cavities blackish; gill rakers and filaments light brown, arches pallid; gular and branchiostegal membranes heavily peppered with small melanophores; all fins uniformly blackish.

Size. To about 44 cm TL ( BSKU 26322 , paratype, 437+ mm TL) .

Distribution. So far known from the Okinawa Trough at depths of 560‾ 815 m (Appendix 3-4E). Uncommon.

Etymology. The specific epithet is derived from the Latin noun nox , meaning “darkness”, in reference to the characteristic dark coloration of the species. The Japanese name, Yami-hige, is derived from a combination of a word meaning darkness (= yami) and a Japanese name for grenadiers (= hige).

Relationships and comparisons. Coelorinchus nox sp. nov. belongs to the C. japonicus group (sensu stricto; see the Relationships of C. japonicus ), and is most closely similar to C. smithi Gilbert & Hubbs, 1920 , with which it has been confused in the East China Sea. The latter species includes at least two morphologically distinct populations, of which one is known from Japan and the other from the East Indies (the type locality of C. smithi is Indonesia; see also the Remarks of the latter species). Coelorinchus nox readily differs from the both populations of C. smithi in having the occipital scales covered with short, erect, needle-like spinules arranged in comb-like ridges (vs. moderately reclined, keel-like to knife-like spinules in saw-toothed ridges; Fig. 78A vs. B), while young specimens of Japanese C. smithi occasionally have a similar spinulation pattern. It is further distinguished from C. smithi from the East Indies by having a relatively short snout (snout length 62–81% PRL vs. 80–86%; preoral length 52–71% PRL vs. 71–80%) and a longer chin barbel (14–22% PRL vs. 10–14%) (see also Table 3 ), and from Japanese C. smithi by its uniformly dark brown coloration ( Fig. 75 vs. distinctly paler ventrally, Fig. 85 A–F). The body of Japanese C. smithi is occasionally darker in larger specimens than smaller specimens ( Fig. 85G ), but it is distinctly paler than that of the new species.

Coelorinchus nox also superficially resembles C. commutabilis Smith & Radcliffe in Radcliffe, 1912 from the East Indies, C. charius Iwamoto & Williams, 1999 from off Western Australia, and C. sereti Iwamoto & Merrett, 1997 from the tropical southwestern Pacific [the holotype of C. commutabilis (USNM 72945, 93.7 mm HL) and type specimens of C. charius (19 spec., 51.3– 98.2 mm HL; including holotype: AMS I.31166-005, 80.6 mm HL) and C. sereti (7 spec., 62.1–124 mm HL; including the holotype: MNHN 1994-925, 119 mm HL) were examined in the course of this study]. However, the new species differs most notably from C. commutabilis and C. charius in that the occipital scales are covered with needle-like spinules in comb-like ridges (vs. keel-like to knife-like spinules in saw-toothed ridges). In contrast, it differs primarily from C. sereti in that the dorsal contour of the snout is moderately concave in lateral view ( Fig. 76B vs. slightly convex; Iwamoto & Merrett 1997: fig. 15a), and the snout is progressively attenuated toward its tip when viewed dorsally, giving a sharply pointed appearance to the snout (vs. broadly convex anteriorly so as to give a much broader appearance to the snout; Iwamoto & Merrett 1997: fig. 15 aʹ). It further differs from C. commutabilis in having fewer pectoral-fin rays (i16–i17 vs. i19–i20), a slightly larger orbit (45–52% PRL vs. 44%), and a shorter postorbital length (49–56% PRL vs. 57%); from C. charius in having a uniformly dark body (distinctly paler ventrally; Iwamoto & Williams 1999: fig. 9); and from C. charius and C. sereti in having a moderately short terminal snout scute (12–17% PRL vs. 19–24% and 9–13% in C. charius and C. sereti respectively) and a narrower internasal width (27–31% PRL vs. 31–35% and 33–37% PRL).

Figures

FIGURE 75. Holotype of Coelorinchus nox sp. nov. BSKU 109205, 99.2 mm HL, 346+ mm TL, Okinawa Trough, East China Sea, 607 m depth. Lateral view. Fresh condition. [Photo: N. Nakayama]

FIGURE 76. Holotype of Coelorinchus nox sp. nov. BSKU 109205, 99.2 mm HL, 346+ mm TL, Okinawa Trough, East China Sea, 607 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 77. Scanning electron micrographs showing a body scale (from the dorsum below the interdorsal space) of Coelorinchus nox sp. nov. BSKU 109205, holotype, 99.2 mm HL. (A) View from above; (B) oblique view. [Photos: NSMT]

FIGURE 78. Photographs showing spinulation of the occipital scales in two species of Coelorinchus. (A) C. nox sp. nov., BSKU 109205, holotype, 99.2 mm HL; (B) C. smithi, BSKU 112398, 94.5 mm HL. Preserved specimens. [Photos: N. Nakayama]

FIGURE 85. Fresh specimens of Coelorinchus smithi. (A–C) BSKU 112403, 55.5 mm HL, 213 mm TL, Tosa Bay off Susaki, Kochi Pref., Pacific, ca. 400 m depth; (D–F) BSKU 112402, 88.0 mm HL, 302+ mm TL, collected with BSKU 112403; (G) KPM- NI 24972, 110 mm HL, 407+ mm TL, off Okinawa-jima Island, Okinawa Pref., 600 m depth. (A, D, G) Lateral, (B, E) dorsal, and (C, F) ventral views. [Photos: (A–F) N. Nakayama; (G) H. Senou]