Coelorinchus lanceolatus, Nakayama, Naohide, 2020

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 94-96

Coelorinchus lanceolatus sp. nov.

[New Japanese name: Yajiri-hige]

( Figs. 62–63 ; Table 1 ; Appendix 3-3E)

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 almost completely naked; dorsal surface of snout fully scaled, except narrow naked clefts along each side of median rostral ridge. Nasal fossa heavily scaled anteroventrally. Snout very long, sharply pointed, length 107% PRL; dorsal profile of snout moderately concave in lateral view. Terminal snout scute long, slender, spearhead-shaped, dorsoventrally flattened, length 27% PRL. Scales on median rostral ridge covered with divergent rows of spinules. Lateral nasal ridge completely supported by nasal bone, almost straight when viewed dorsally, giving sharply pointed and distinctly attenuated appearance to snout. Anus slightly separated from anal-fin origin. Premaxillary teeth small, conical, arranged in short, uniformly wide band, none especially enlarged; posterior margin of tooth band falling far short of lateral corner of mouth. Body scales covered with short, reclined, keel-like spinules in narrowly divergent, saw-toothed ridges; every spinule row complete, extending to posterior scale margin; spinules in each row greatly overlapping, closely adjoined to one another, but generally free at tips; buttresses only narrowly developed. Occipital scales covered with short, erect, keel-like spinules in widely divergent, saw-toothed rows. Postorbital length 53% PRL; preoral length 101% PRL; prepelvic length 227% PRL; preanal length 292% PRL; predorsal length 214% PRL; height of first dorsal fin 84% PRL; interdorsal length 34% PRL. Free neuromasts on underside of head tiny, immaculate, difficult to distinguish; dark hair-like papillae absent on underside of head. Body uniformly pale in preserved specimen; lips white; oral cavity blackish.

Material examined. 1 specimen. Holotype: NSMT-P 95590 (79.2 mm HL, 255+ mm TL), east of Muko-jima Island , Ogasawara Islands, Shichito-Iojima Ridge, Japan, 521–536 m, R/ V Tansei-maru, cr. KT-97-07, sta. MK05, 3-m ORE beam trawl, 7 Jun. 1997.

Description. General features are shown in Fig. 62 . Counts and measurements are given in Table 1 . Body deepest at first dorsal-fin origin, tapering gradually to long laterally compressed tail. Trunk shallow, width over pectoral-fin bases 1.1 in depth below first dorsal-fin origin. Head large, HL about 3.2 in TL. Snout very long, sharply pointed, protruding greatly beyond upper jaw, length 2.3 times as long as orbit diameter; dorsal contour of snout moderately concave in lateral view; lateral nasal ridge completely supported by nasal bone, almost straight in dorsal view, giving sharply pointed and distinctly attenuated appearance to snout. Orbit large, greatest diameter 1.1 in postorbital length. Interorbital space flat, width 1.2 in orbit diameter. Mouth moderate in size, inferior,protrusible, upper-jaw length 1.2 in orbit diameter; posterior margin of maxilla reaching vertical through hind 2/5 of orbit; lateral corner of mouth moderately 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 at about 60º angle, 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 slight posterior free fold. Outer gill slit moderately restricted by skin folds, length 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 slender, length 3.7 in orbit diameter, tapering into filamentous tip.

Anus only slightly separated from anal-fin origin by 1–2 scale rows. Light organ externally represented by short, narrow, naked streak, extending from anus forward to midway between anus and outer pelvic-fin base, its anterior margin 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 7 tooth rows across widest point near symphysis, posterior margin of tooth band falling far short of lateral corner of mouth; teeth becoming progressively smaller inwardly. Mandibular teeth in broad tapered band, with about 5 tooth rows near symphysis; mandibular band narrowing gradually to about 3 rows posteriorly, its posterior margin extending beyond lateral corner of mouth; all teeth uniformly small.

Body scales large, thin, not deciduous; those on dorsum below interdorsal space covered with short, reclined, keellike spinules in 6–7 narrowly divergent rows ( Fig. 63 A–B); middle row longest with about 7 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 often free, forming saw-toothed ridges that give spiny appearance to body surfaces; spinules increasing in height posteriorly, and tip of last spinule in each row extending slightly 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 coarsely modified; those on median rostral ridge covered with radiating rows of spinules. Terminal snout scute very long, slender, attenuated, spearhead-shaped, dorsoventrally flattened, its length 1.7 in orbit diameter. Supraoccipital and posttemporal scutes stout, but not especially enlarged. Occipital scales covered with short, erect, keel-like spinules in narrowly divergent, saw-toothed rows ( Fig. 63 C–D); those on dorsal surfaces of snout posterior to leading edges armed with 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 and more or less needle-like in shape; those on opercle, preopercle, and postorbital and supratemporal canals largest. Nasal fossa heavily scaled anteroventrally. Dorsal surfaces of snout almost fully scaled; naked clefts along each side of median rostral ridge narrowly developed. Underside of head completely naked.

No open pores along cephalic sensory canals. Free neuromasts tiny, poorly marked, not discernible. Anterior nostril small slit; posterior large, oval in shape. Grooved lateral line complete, not interrupted throughout.

Origins of first dorsal and pelvic fins on about same vertical; first dorsal fin moderately high, its height 2.9 times as long as its base length; second spinous ray not elongated, smooth along its leading edge; its tip extending posteriorly to base of 5th ray of second dorsal fin when laid back. Interdorsal space 1.1 times as long as first dorsal-fin base length. Origin of second dorsal fin above base of 2nd ray of anal fin. Tips of pectoral and pelvic fins extending slightly beyond vertical through anal-fin origin when laid back; outer pelvic-fin ray slightly prolonged, filamentous at tip.

Color when fresh. Unknown.

Color in alcohol ( Fig. 62 ). Head and body uniformly light brown; abdomen darker; lips white; oral cavity faded, but probably blackish originally; gill cavity blackish; gill rakers and arches pale, filaments light tan; fins uniformly pale, but second spinous ray of first dorsal fin slightly darker distally.

Size. To at least 26 cm TL.

Distribution. So far known from off the Ogasawara Islands, Shichito-Iojima Ridge, at a depth of 521‾ 536 m (Appendix 3-3E). Very rare.

Etymology. The specific epithet is derived from the Latin adjective lanceolatus , meaning “armed with a lance”, in reference to the species’ long snout tipped with a spearhead-shaped scute. The Japanese name, Yajirihige is derived from a combination of the Japanese nouns “yajiri”, meaning a spearhead, and “hige”, meaning grenadiers.

Remarks, relationships, and comparisons. Coelorinchus lanceolatus sp. nov. is represented by only a single specimen collected from the Shichito-Iojima Ridge, Japan. It belongs to the C. anatirostris group in having the following combination of features (see the Relationships of C. anatirostris ): light organ externally represented by short naked streak anterior to anus, its anterior margin not reaching line connecting inner pelvicfin bases; lateral nasal ridge completely supported by nasal bone; premaxillary teeth in short, uniformly wide band; underside of head completely naked; body scales covered with keel-like spinules in narrowly divergent rows, and every row complete throughout; buttresses of scale spinules narrowly developed; no prominent markings on body. Coelorinchus lanceolatus is similar to C. anatirostris Jordan & Gilbert in Jordan & Starks, 1904 in many aspects, and the holotype of the former was initially considered to represent an unusual variant of the latter species. Actually, the two species share the most useful diagnostic features distinguishing C. anatirostris from its congeners, and no significant differences are found in meristic characters. However, C. lanceolatus differs notably from C. anatirostris in having a distinctly longer snout [107% PRL ( Fig. 62 ) vs. 60–88% ( Figs. 18– 20 , 24 )] with a well-developed terminal scute (27% PRL vs. 7–18%). The difference in the snout length is too great to ignore, even considering the variation of C. anatirostris in this study, which causes other pronounced differences in measurements, including the preoral length (101% PRL in C. lanceolatus vs. 50–81% in C. anatirostris ), prepelvic length (227% PRL vs. 184–214%), preanal length (292% PRL vs. 239–380%), and predorsal length (214% PRL vs. 177–205%). In addition, C. lanceolatus has a relatively lower first dorsal fin than C. anatirostris (84% PRL vs. 85–107%). Despite limited study material, there is little doubt that the specimen represents a distinct species previously unknown to science.

The new species is also similar in many aspects with C. weberi Gilbert & Hubbs, 1916 known only from the holotype collected from the Philippines. However, C. lanceolatus is readily distinguished from the latter species in that free neuromasts on the underside of the head are unpigmented and difficult to distinguish without a microscope (vs. each neuromast marked with two small black dots). It further differs notably from C. weberi by having a longer snout (107% PRL vs. 80%), shorter postorbital (53% PRL vs. 58%), and lower first dorsal fin (84% PRL vs. 99%). A pronounced difference between the two species was also found in the snout shape. In C. lanceolatus , the anterolateral margins of the snout are almost straight when viewed dorsally, giving a sharply pointed and distinctly attenuated appearance to the snout, whereas those of C. weberi are broadly convex so as to give a spade-shaped appearance to the snout. The latter species will be fully redescribed in a forthcoming paper by the present author.

Figures

FIGURE 18. Fresh specimens of Coelorinchus anatirostris. (A) BSKU 109032, 90.6 mm HL, 354+ mm TL, Okinawa Trough, East China Sea, 351–389 m depth; (B) BSKU 109033, 79.7 mm HL, 318+ mm TL, collected with BSKU 109032; (C–E) BSKU 102003, 73.1 mm HL, 283+ mm TL, Mimase fish market, Kochi, Pacific. (A–C) Lateral views; (D) dorsal and (E) ventral views of the head and trunk. [Photos: N. Nakayama]

FIGURE 19. Holotype of Coelorhynchus anatirostris (= Coelorinchus anatirostris). USNM 51471, 93.7 mm HL, 395 mm TL, Sagami Bay off Misaki, Kanagawa Pref., Pacific. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 20. Preserved specimen of Coelorinchus anatirostris. USNM 76865, holotype of Coelorhynchus productus, 79.9 mm HL, 304 mm TL, Suruga Bay, Shizuoka Pref., Pacific, 544–361 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. [Photos: N. Nakayama]

FIGURE 24. Variation of the snout shape in Coelorinchus anatirostris. [Photos: N. Nakayama]

FIGURE 62. Holotype of Coelorinchus lanceolatus sp. nov. NSMT-P 95590, 79.2 mm HL, 255+ mm TL, off Ogasawara Islands, Shichito-Iojima Ridge, Pacific, 521–536 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 63. Scanning electron micrographs showing scales of Coelorinchus lanceolatus sp. nov. NSMT-P 95590, holotype, 79.2 mm HL. (A–B) Scales from the dorsum below the interdorsal space; (C–D) from the top of the head between the parietal ridges. (A, C) Views from above; (B, D) oblique views. [Photos: N. Nakayama]