Coelorinchus paraboliceps, Prokofiev & Iwamoto, 2020

Prokofiev, Artem M. & Iwamoto, Tomio, 2020, Revision of the Grenadier Genus Coelorinchus (Teleostei: Macrouridae) from the Mascarene Ridge, Western Indian Ocean, with Description of Two New Species, Proceedings of the California Academy of Sciences 66 (9), pp. 231-273 : 241-243

Coelorinchus paraboliceps new species

Figures 2C , 5G–I , 6C–D , 7C–D , 14 , 15

Coelorinchus sp. B : Shcherbachev et al. 1986:201 (6°20´S, 54°23´E).

Holotype. — IOM M.004–003 (120 mm HL, 410+ mm TL), Mascarene Ridge, 8°26.4´S, 59°29´E, 1300– 1260 m, FRV Fiolent, cruise 7(9), trawl 52, 2 Sept. 1977.

DIAGNOSIS.— A species of the Coelorinchus acanthiger –group with light organ not evident externally; snout 40 % HL, with sides strongly and regularly convex in dorsal view; medial element of terminal scute small, its length 3.3 % HL; preoral region largely naked at 120 mm HL, nasal fossa mostly scaleless, area between nasal fossa, orbit, and suborbital ridge fully scaled; scales over interorbital space with spinules not forming clear keel-like rows; scales on body firmly attached, bearing spinules with buttresses strongly developed, forming concentric ridges even on scales below and in front of first dorsal fin and on scales from tail; 3.5 and 4.5 scales between midbase of first dorsal fin and between origin of second dorsal fin and lateral line, respectively; body medium brown, fins darker, lips and gums pale.

DESCRIPTION.— General features of fish seen in Figs. 2C , 14 . Counts: first dorsal-fin rays ii + 6; pectoral-fin rays i + 18; pelvic-fin rays 7; gill-rakers (inner) on 1 st arch 7; gill-rakers on 2 nd arch 6 (outer) / 7 (inner); transverse scale rows below origin of first dorsal fin 4.0; ditto, below midbase of first dorsal fin 3.5; ditto, below origin of second dorsal fin 4.5; ditto, between origin of anal fin and lateral line 14; lateral-line scales before origin of second dorsal fin 12; pyloric caeca not counted (stomach everted).

Measurements shown in Table 2 . Width of body across pectoral bases 78.2 % of greatest body depth (at dorsal-fin origin), 1.3 times less than greatest width of head (at preopercles). Head c. 3.4 times in TL. Snout moderately long and rather broad, 2.5 times in HL, 1.1 times greater than postorbital length of head. Snout bluntly pointed in lateral view, with dorsal contour gently declining toward the tip, slightly convex at level of nasal fossa ( Fig. 14A ); strongly convex at sides in dorsal view, with tip somewhat angularly rounded ( Figs. 14B, 14C ). Snout tipped with short rectangular terminal scute consisting of transversely extended medial element and small squarish lateral elements ( Fig. 15A ). Anterolateral margins of snout not completely supported by bone. Orbit elliptical, 4.3 times in HL, 1.7 times in snout. Suborbital shelf moderately angulated; shelf depth 1.6 times in suborbital depth. Lateral nasal ridge 3.7 times shorter than suborbital ridge. Mouth large, posterior tip of maxilla extending below posterior quarter of orbit, rictus extending just behind vertical through middle of orbit. Preopercle inclined backward at about 65º, with moderately long, broadly and somewhat angularly rounded posteroventral lobe having roughly crenate free margin. Subopercle terminates ventrally in slender tip that extends somewhat beyond preopercle. Chin barbel short, slender, 3.1 times in orbit. Free neuromasts on snout, along head ridges and on underside of head prominent, more or less infuscated (brownish to blackish); black hair-like papillae poorly developed on dorsal surface of head, numerous on underside below suborbital ridge and in preoral region (especially in area in front of premaxillary symphysis). Inner side of gill opening with shallow ridge-like protrusion in its lower half.

Jaw teeth conical, rather thin (needle-like), in narrow bands; premaxillary teeth larger than those on dentary; outermost teeth of premaxilla somewhat enlarged. Premaxillary tooth band short, 1.9 times in length of rictus; dentary tooth band reaching end of rictus.

First dorsal-fin base 1.5 times shorter than the interdorsal space; second dorsal-fin spine with very short filament (reaching origin of second dorsal fin only). Pectoral fin narrow based, short, falling well before anus. Pelvic fin originates behind the vertical of pectoral-fin base. Outermost pectoral-fin ray filamentous and extending to anus. Anus close to anal-fin origin. Light organ not externally visible.

Squamation ( Figs. 5G–I , 6C–D , 7C–D ). All scales strong and adherent, those on body large; those on flanks, on tail, and on belly with spinules arranged in parallel rows; those in predorsal region, on cheek, opercle, and isthmus arranged in more or less diverging rows. Spinules on scales below first dorsal-fin base arranged in 5–6 (7) rows; those on scales below beginning of second dorsal fin arranged in 6–8 rows; rows incomplete (except middle one); middle row of spinules distinctly enlarged and raised, giving appearance of horizontal striations on body surface; spinules in rows gradually increasing in length posteriad. Spinules on tail behind anterior quarter of anal-fin base with spinules more inclined backward and with last spinule of middle row much produced behind posterior margin of scale. Each spinule with prominent lateral buttresses often joined with those of neighboring rows to form low transverse ridges across exposed field of scale (buttresses well-developed and joined with those of neighboring rows even on tail scales). Predorsal scales smaller in size than those on flanks, with similarly erect but shorter spinules, arranged in 3–4 rows. Scales on top of head chiefly with more or less diverging rows of spinules; however, spinules often situated so irregularly that rows becoming indistinguishable; all spinules with prominent lateral buttresses. Area between the orbit, nasal fossa, and suborbital ridge fully scaled, with spinules on scales arranged mostly in clusters. Narrowest portion of suborbital shelf bearing about 4 rows of tightly joined scales between lower rim of orbit and upper edge of suborbital ridge (lowermost row consisting of scales much larger in size). Nasal fossa largely scaleless (few minute spinulose scales present on right side at anterodorsal and anteroventral margins of fossa, and two minute cycloid scales found on left side at anterodorsal margin of fossa). Top of snout densely scaled. Underside of head largely scaleless in preoral region except small area behind terminal scute and lateral quarters of posterior third of preoral length, where densely scaled ( Fig. 15B ); also densely scaled behind the level of premaxillary symphysis toward the preopercular lobe and on mandibular rami; naked on gular region and branchiostegal membranes; scales adherent. Spinules on scales from underside of head arranged in a cluster or in a single short row. Scutes of head ridges strongly armed with numerous rather long and stout conical spinules with pointed tips; scutes of medial nasal ridge with radiating rows of spinules having conspicuous lateral buttresses, 9 scutes in number (including terminal scute). Supraoccipital and postoccipital scutes small, not larger than neighboring scales, coarsely spinulated.

Body color medium brown without markings. Brown coloration formed by dense aggregations of melanophores on epithelium covering the exposed field of the scales. When scales removed, scale pockets pure white with narrow dark-brown margins and with variably expressed concentrations of brownish to blackish melanophores along posterior margins (poorly expressed on scale pockets from dorsal half of body and from breast and tail, conspicuous and broad on lower parts of trunk and on belly). Orbit encircled by dark-brown ring; anterior border of second naris blackish. Preoral area infuscated, gular region and branchiostegal membranes much darker, becoming blackish on upper reaches of branchiostegal membrane. Lips and gums as well as mouth cavity pale, gustatory papillae pale except minute dark-brownish papillae along outer margin of lower lip; branchial cavity blackish; stomach pale. Anal fin blackish; other fins less dark, more or less dusky, basal third of dorsal fin apparently much darker than rest of fin.

ETYMOLOGY.— Derived from “parabola” (a kind of graphics with all points equidistant from the given straight line) and “ceps” (Latin, a head), in allusion to the characteristically shaped snout in dorsal view; noun in apposition.

REMARKS.— Shcherbachev et al. (1986) reported as Coelorinchus sp. B two specimens, 59 and 73.6 mm HL, collected during the second cruise of R / V Rift at 6°20´S, 54°23´E. We were unable to find these specimens for the current study but a brief description provided by Shcherbachev et al. (1986) leaves no doubt as to their conspecificity with the holotype of C. paraboliceps . The Rift specimens have snout lengths of 40.8–44.1 % HL, preoral region almost scaleless, 4.0 scales between midbase of first dorsal fin and lateral line; flank scales with overlapping spinules, their rows not numerous; and external light organ absent.

The new species is notably different from all other Mascarene Coelorinchus in the shape of the medial element of the terminal scute of the snout, which is small and rectangular in shape in contrast to the acuminate and diamond-shaped element in the other species. However, the new species shows other differences ( Table 4 ) that support its separation. 1

COMPARISONS — The new species is most similar to C. yurii but can be easily distinguished from that species in the preoral region largely scaleless (vs. completely scaled except for a small triangular area in front of premaxillary symphysis), and in the buttresses of spinules forming harsh transverse ridges even on scales in front and below first dorsal fin and on tail (vs. transverse ridges poorly developed to absent) ( Figs. 5G–L , 6D, 6F , 7D, 7F ). See Table 4 for additional minor differences and for comparison with C. amirantensis , another closely similar species. Overall, the buttresses of the scale spinules appear to be more highly developed, and the transverse crests across the scales formed by the buttresses are harsher in the new species than in any other Mascarene Coelorinchus ( Figs. 5–7 ). The stability of these features requires confirmation with more extensive material.

Within the extralimital species, C. paraboliceps is reminiscent of C. trachycarus from the Tasman Sea and southern Australia; however, the latter species differs by its more extensive naked areas along the suborbital and lower preopercular margins, by its snout being sharply pointed and weakly convex at sides in dorsal view, and by its shorter postorbital length (22–32 % HL, orbit into postorbital 1.0–1.2 times vs. 36.7 % and 1.6 times in C. paraboliceps ).

Figures

FIGURE 2. Coelorinchus spp., habitus, lateral view. A. C. amirantensis, IOM M.008–002, paratype, 108 mm HL. B. C. mascarenus, IOM M.011–007, holotype, 91 mm HL. C. C. paraboliceps, IOM M.004–003, holotype, 120 mm HL. D. C. yurii, IOM M.003–017, non-type specimen, c.156 mm HL.

FIGURE 5. Coelorinchus spp., isolated scales from predorsal region (A, D, G, J), from flank between first dorsal-fin origin and lateral line (B, E, H, K), and from flank between second dorsal-fin origin and lateral line (C, F, I, L) (stained by alizarine red S for contrast). A–C. C. amirantensis, IOM M.007–001, paratype. D–F. C. mascarenus, IOM M.011–007, holotype. G–I. C. paraboliceps, IOM M.004–003, holotype. J–L. C. yurii, IOM M.003–017, non-type specimen. Scale bars: A, J, 2.5 mm. B, C, E, F, H, K, 3.0 mm. D, 1.5 mm. G, 2.0 mm. I, L, 3.5 mm. Scale bar is common for E and F.

FIGURE 6. Coelorinchus spp., squamation of interorbital region (A, C, E) and of flank between mid-base of first dorsal fin and lateral line (B, D, F). A, B. C. amirantensis, IOM M.007–001, paratype. C, D. C. paraboliceps, IOM M.004–003, holotype. E, F. C. yurii, IOM M.003–017, non-type specimen. Scale bars: A, C, E, 2.5 mm. B, D, F, 5.0 mm.

FIGURE 7. Coelorinchus spp., squamation of flank between origin of second dorsal fin and lateral line (A, C, E) and of tail behind anterior third of second dorsal-fin base (B, D, F). A, B. C. amirantensis, IOM M.007–001, paratype. C, D. C. paraboliceps, IOM M.004–003, holotype. E, F. C. yurii, IOM M.003–017, non-type specimen. Scale bars: 5.0 mm.

FIGURE 14. Coelorinchus paraboliceps, IOM M.004–003, holotype, 120 mm HL. A. Lateral view of head. B. Dorsal view of head. C. Ventral view of head.

FIGURE 15. Coelorinchus paraboliceps, IOM M.004–003, holotype. A. Terminal scute of snout (arrowed), dorsal view. B. Preoral region. Scale bars: A, 1.5 mm. B. 5.0 mm.