Coelorinchus tricristiger, Prokofiev & Iwamoto, 2022

Prokofiev, Artem M. & Iwamoto, Tomio, 2022, A new species of the grenadier genus Coelorinchus (Gadiformes: Macrouridae) from the western Indian Ocean, Zootaxa 5194 (2), pp. 193-212 : 195-207

Coelorinchus tricristiger sp. nov.

Figs. 1–4 , 6 ; Table 2

Holotype. IOM M.120–009, TL 197+ mm, HL 57 mm, R / V Vityaz-II, cruise 17, sta. 2573, 10°20′– 10°16′ N, 56°07′ E, 408–415 m, bottom shrimp trawl 19.4 m, 30 Oct. 1988.

Paratypes. CAS 228399 , 5 (TL 181+–202+ mm, HL 33–40 mm) , R / V Beinta , cruise 19, sta. 24, Somalia, 9°04′42″ N, 50°51′20″ E, 178–182 m, 14 Feb. 1987, coll. Greg Small ; IOM M.120–001 to 008, 010 to 033, 44 (TL 107–228+ mm, HL 29–67+ mm), and CAS 66483, 8 (TL 125+–195+ mm, HL 37–56+ mm), collected with the holotype ; IOM M.122–001 and 002, 2 (TL 192+–206+mm, HL 56–57 mm), R / V Vityaz-II, cruise 17, sta. 2560, 12°18′– 12°14′ N, 53°09′– 53°06′ E, 375–380 m, bottom shrimp trawl 19.4 m, 27 Oct. 1988 ; IOM M.125–001 to 012, 12 (TL 119+–214+ mm, HL 36–56+ mm), and CAS 66489, 12 (TL 135+–224+ mm, HL 36–60+ mm) , R / V VityazII, cruise 17, sta. 2825, 10°19′30″ N, 56°08′48″ E, 420– 395 m, bottom shrimp trawl 29 m, 14 Jan. 1989 .

Diagnosis. A species of the Coelorinchus hubbsi complex as defined by Okamura (1984) and Nakayama et al. (2020) with transversely banded pattern on body, no isolated suprapectoral spot, and third transverse band diagonally inclined and extending forward to pectoral-fin base. The new species can be distinguished from similarly colored species ( C. cingulatus , C. fuscigulus , C. melanosagmatus , C. spilonotus ) by the presence of a long medial occipital ridge consisting of 4 to 7 (usually 5 or 6) enlarged scutes and the absence of a ventral projection of the subopercle.

Description. General features seen in Fig. 1A . Counts: first dorsal-fin rays, ii+8 [ii+8, rarely ii+7 or ii+9]; pectoral-fin rays, i+18 [i+14–18, modally i+16]; pelvic-fin rays, 7; gill-rakers (inner) on 1 st arch, 6 [5–8]; gill-rakers on 2 nd arch, 5 [5–8] (outer) / 6 [5–8] (inner); transverse scale rows below origin of first dorsal fin, 5.5 [4.5–6.5, usually 5.5]; transverse scale rows below midbase of first dorsal fin, 4.0 [3.0–4.5]; transverse scale rows below origin of second dorsal fin, 4.0 [4.0–6.0, usually 4.5–5.5]; transverse scale rows between origin of anal fin and lateral line, 12 [10–15, most often 11–12]; lateral-line scales before origin of second dorsal fin, 14 [12–14, rarely 15]; pyloric caeca, 22–27 (n = 5). Measurements shown in Table 2 . Head 3.5 [3.3–4.0, usually 3.6–3.8] times in TL. Snout long and sharply pointed, tipped with narrow-lanceolate, acute, strongly attenuated terminal scute, ~ 5 [4.0–4.5] times in snout length (3.0 and 3.4 times in two smallest specimens 29 mm HL). However, in most larger specimens examined (HL> 43 mm), about a third to two-thirds of distal part of terminal scute are missing or worn down resulting in a much shorter and rather obtuse snout. When terminal snout scute is complete or nearly so ( Figs. 1B, C , 2A ), snout length contained 2.4 [2.1–2.8] times in HL, while in specimens with strongly worn terminal scute ( Fig. 2B, C ), its length decreases to 2.9–3.3 times HL. Snout length excluding terminal scute, 2.9 [2.8–3.6] times in HL. Postorbital length of head 1.3 [1.0–1.3] times shorter than snout. Dorsal contour of snout slightly concave in front of nostrils; sides in dorsal view strongly convergent and slightly concave from near midlength of lateral nasal ridge toward terminal scute, straight and moderately convergent before this midlength ( Figs. 1B , 2A–C ). Anterolateral margins of snout not completely supported by bone. Orbit elliptical, 4.1 [3.1–4.1] times in HL, 1.4 [1.1–1.5, usually 1.2 or 1.3] times in postorbital length of head. Suborbital shelf sharply angulated; shelf depth 1.7 [1.3–1.9] times in suborbital depth. Lateral nasal ridge 3.1 [2.7–4.5, usually 3.0–3.7] times shorter than suborbital ridge. Mouth moderately large, posterior tip of maxilla ending at posterior third of pupil to midway between hind margin of pupil and hind border of orbit. Jaw teeth uniformly short, needle-like, densely clustered in bands that are broadened toward symphysis; teeth on premaxilla larger than those on dentary; outermost premaxillary teeth not enlarged, their tips expressed through upper-lip margin. Premaxillary tooth band 1.8 [1.5–2.1, usually 1.8–2.0] times shorter than length of rictus; dentary tooth band reaching rictus. Lips rather thin, very finely papillose in symphyseal area (magnification required). Preopercle margin inclined backward at about 65º, with posteroventral lobe broadly rounded; subopercle lacking a ventral projection. Chin barbel slender, 2.6 [2.7–3.8, 2.4 in one specimen] times in orbit. Length of first gill slit 5–14 % HL (n = 17). Free neuromasts on head mostly encircled by brownish pigment but not very conspicuous, more pronounced though rather sparsely distributed in preoral region.

First dorsal-fin base 1.2 [1.0–2.0, usually 1.2–1.8] times longer than interdorsal space; second dorsal-fin spine 1.6 [1.4–2.0] times in HL, extended distally into a short filament. Rays of second dorsal fin nearly as long as those of anal fin. Pectoral fin narrow based, reaching slightly behind anal-fin origin. Pelvic fins originate at vertical of pectoral-fin origin or slightly behind, but usually before vertical of first dorsal-fin origin. Outermost pectoral-fin ray filamentous, ending at or just behind anus in juveniles, not reaching anus in adults. Anus near anal-fin origin. Light organ long, consisting of anterior and posterior fossae connected by a longitudinal strip; front border of anterior fossa closer to tip of isthmus than to pelvic-fin origin.

Trunk flank scales moderately adherent in larger individuals, bearing 5–14 (number increasing with growth, 8 or more in specimens HL ≥ 45 mm) slightly diverging rows of sharp, narrowly lanceolate, semi-erect spinules; spinules in rows uniform in size and shape, separated from each other; all rows complete; spinules in medial row not enlarged ( Fig. 3B ). Tips of posteriormost spinules in rows extending well behind hind margin of scale. Spinules on tail scales are similar to those on trunk flank scales but much more depressed; spinules on scales from isthmus and abdomen are smaller and more numerous than on scales from trunk flanks. Predorsal scales with larger and more erect spinules arranged in 3–6 clearly diverging rows, medial row sometimes slightly enlarged ( Fig. 3A ). Scales on top of head with 3–6 diverging rows of sharp erect spinules, uniform in size. Medial occipital ridge present, consisting of 5 [5–7, usually 5 or 6, 4 in one specimen] supraoccipital scutes. Postoccipital scute as large as neighboring scales but distinguished by much larger and coarser spinulation, similar to those on ridge scutes. Spinulation on cheek and opercle scales in strongly diverging rows (up to 11 rows on opercle, up to 6 rows on cheek); those on opercle with spinules in rows clearly larger and more erect than on flanks. Spinulation on cheek scales differ depending on location of scale: those behind posteroventral margin of orbit bear rather coarse and sparse, erect spinules with medial row sometimes slightly enlarged. Postorbital scales between postorbital ridge and a horizontal line through ventral margin of pupil bear minute, uniform, semi-erect spinules. Dorsal surface of snout with narrow, elongate, scaleless area on each side; nasal fossa totally devoid of scales or with one to few isolated scales in a row along its anteroventral or ventral border, never clustered (on both sides in 34% of studied specimens HL≥ 45 mm, one side only in 28% of specimens); area between nasal fossa, orbit and suborbital shelf with few small spinulose scales; underside of head scaleless. Suborbital shelf with two rows of moderately small squarish scutes; scutes of medial nasal ridge 8 [7–8, 9 in one specimen] in number (including terminal scute), with radiating rows of spinules.

In preserved fish, body color pale with dark brownish markings ( Figs. 1A , 4 ); margins of scale pockets more densely peppered by brownish melanophores. Head with indistinct infuscation along ridges and rather regular and dense dotting of minute melanophores on scales; top of head with very vague dark speckled pattern formed by concentration of melanophores on posterior fields of most scales and along ridges; melanophores becomes much larger and pronounced ventrally along suborbital ridge and on underside of head; branchiostegal membranes dark brownish. Opercle usually with a more or less extensive dark area dorsoposteriorly.Lips and gums pale, unpigmented; mouth inside premaxillary symphysis pale, otherwise brownish like underside of gill cover. Occipital ridges are slightly to substantially darker than the surrounding ground, often with a dark blotch-shaped area at their ends, usually more pronounced and extensive at end of medial ridge; more or less pronounced longitudinal infuscation often present between lateral occipital and postorbital ridges, sometimes connecting with that on opposite side through occiput behind endings of occipital ridges. A conspicuous transversely extended saddle-like band at first dorsal-fin origin, running down to pectoral fin base, not confluent with that mark on opposite side in front of first dorsal-fin origin. Most often this band is bar-like, but clearly narrower above lateral line than below (2–4 and 4–6 scale rows in width, respectively), showing a blotch-like lower portion, extending to first dorsal-fin base by a narrower strip ( Fig. 4A ); rarely this band is in form of transversely extended blotch, diamond-shaped or bar-like but of nearly equal width (4–5 scale rows) above and below lateral line ( Fig. 4B, C ). Usually, this band is margined by extensive pale areas along its anterior and posterior border giving an “ocellate” appearance, although in some specimens these can be indistinct or expressed along anterior border only. Subsequent pronounced dark band situated below origin of second dorsal fin, connecting with that on opposite side through the dorsum (and expressed in blackish rays of second dorsal fin), widest above lateral line (4–5 scale rows), diagonally inclined and running forward to pectoralfin base but strongly diffusing and often disappearing below level of upper end of pectoral-fin base. A much more diffuse light-brownish triangular or bar-like saddle-mark often present between these two conspicuous dark bands (situated below the first dorsal-fin base). A pronounced dark-brownish saddle-like band connecting with those on opposite side present at ending of anterior third of second dorsal fin, 4–6 scale rows in width, usually short and not reaching the lateral line, but sometimes extending forward along the lateral line (where it is much more diffuse). Two or three inconspicuous agglomerations of dark pigment or indistinct saddles may be present dorsally farther back on tail. Scales on lower sides, isthmus and abdomen with numerous large well-separated black melanophores. Subdermal melanophore pigmentation present below lateral line, becoming much larger and denser on isthmus and abdomen. First dorsal fin conspicuously bicolored, blackish in distal two-thirds. Second dorsal-fin rays pigmented above saddle marks to same degree; rays in anterior third of anal fin and of distal parts of second dorsal and anal fins blackish. Pectoral fin indistinctly speckled with light-brownish melanophores. Pelvic fin dark-brownish to blackish, outermost ray whitish. Peritoneum pale and densely peppered with minute dark melanophores interspersed with much sparser larger melanophores.

Ontogenetic variations. Juvenile specimens (29–43 mm HL) differ by having more deciduous body scales, more spinulose head ridges, and fewer rows of spinules on scales (5–7 rows on flank scales vs. 8–14 in specimens 45 mm HL or larger). Mean values of many measurements are different from those in larger specimens (HL ≥ 45 mm), but dispersion of individual variation is nearly the same in both size classes ( Table 2 ). We find no clear trends in change with growth for any measurement. Morphometric analysis is complicated by considerable wear of the terminal scute in most specimens over 45 mm HL. Among 45 specimens collected in a single haul from Vityaz-II sta. 2573, 12 of 14 specimens 29–43 mm HL possessed a complete terminal scute, but only 4 of 31 larger specimens 45–67+ mm HL had a complete scute—this despite the more fragile nature of the smaller specimens, whose snout is easier to damage. In most larger specimens with a worn or missing terminal scute, free outer sides of scute lack traces of fresh fractures ( Fig. 2D, E ), suggesting possible wear during life. The terminal snout scute in the studied juveniles is often retained and complete, even when the lateral nasal ridge is damaged. The pigment pattern is less prominent, but in general, similar to that in larger specimens. The pale margins of the first saddle-like band on flank of body become traceable at about 40 mm HL.

Etymology. The species epithet is created from the Latin words “ tres ” (three), “ crista ” (crest), and “ gero ” (to carry) and reflects the most peculiar feature of this species: the presence of three complete occipital ridges; indeclinable noun.

Figures

FIGURE 1. Coelorinchus tricristiger sp. nov., holotype, IOM M.120-009, 197+ mm TL, 57 mm HL, preserved. A. Lateral view. B. Head, dorsal view. C. Head, ventral view. Captions: 1, scaleless area on top of snout; 2, medial occipital ridge. Scale bars: 15 mm (common bar for B and C).

FIGURE 2. Coelorinchus tricristiger sp. nov., shape of snout and terminal snout scute, paratypes. A–C. Dorsal view of head. A. IOM M.122-001, 57 mm HL. B. IOM M.120-015, 56+ mm HL. C. IOM M.120-022, 55+ mm HL. D, E. Terminal snout scute showing spination and total size apparently worn down with use, IOM. M.120-015. D. Dorsal view. E. Anteroventral view, see longitudinal ridges extending onto anterior face. Scale bars: A–C, 10 mm; D, E (common bar), 3 mm.

FIGURE 3. Coelorinchus tricristiger sp. nov., holotype, IOM M.120-009, isolated scales.A. Predorsal region. B. Flank below first dorsal-fin base. Scale bar (common): 1 mm.

FIGURE 4. Coelorinchus tricristiger sp. nov., variations in shape of first saddle-mark on flank, paratypes. A. M.120-001, c.61 mm HL. B. M.120-022, 55+ mm HL. C. M.120-032, 48+ mm HL. Scale bars: 10 mm.

FIGURE 6. Distribution of Coelorinchus tricristiger sp. nov. and other similarly banded species (see comparative material examined for information about specimens). A single symbol may indicate more than one capture.