Tenuicephalus multitrabs, Schwarzhans & Møller, 2021

Schwarzhans, Werner W. & Møller, Peter R., 2021, Revision of the ‘ dragon-head’ cusk eels of the genus Porogadus (Teleostei: Ophidiidae), with description of eight new species and one new genus, Zootaxa 5029 (1), pp. 1-96 : 77-79

Tenuicephalus multitrabs n. sp.

Figs. 4 , 39–40 , 48 , 51 , Tab. 1–7

Porogadus sp : Shcherbachev 1980: 92.

Material examined ( 13 specimens): Holotype CAS 83066-3 , 153 + mm SL, R / V Fishery Researcher 1, Philippines, Lagonoy Gulf, 13°20’30”N, 124°16’30”E, 30 m otter trawl, 1037–1100 m, collected by Tomio Iwamoto and party, 24 September 1995; paratypes: CAS 83066- 2, 156 mm SL, same data as holotype; MNHN 1994-0761 , 202 mm SL, 22°06’S 166°27’E, 1920–2040 m, R / V Coriolis, Biogeocal Expedition, Sta. co273, 20 Apr 1987; MNHN 1997- 0381 , 133 mm SL, 14°52’S 167°18’E, 1550–1620 m, R / V Alis, Musorstom 8 Expedition, Sta. cp1109, 08 October 1994; ZMMGU 15104, 176 mm SL, R / V Fiolent, Cruise 9, trawl 22, 13 June 1977, 11°24’S 88°50’E, 1650 mm,; ZMMGU 15105, 180 mm SL, R / V Fiolent, Cruise 9, trawl 25, 11°36S 87°50’E, 1800–2000 m, 19 June 1977; ZM- MGU 15172, 202 mm SL, R / V Prof. Mesyatzev, Cruise 7, trawl 15, 11°31’S 88°55’E, 1600–1700 m, 18 March 1979; ZMMGU 15173, 175 mm SL, R / V Prof. Mesyatzev, Cruise 7, 14°30’S 88°12’E, 1820–1880 m, 18 March 1979; ZMMGU 15174 , 175– 195 mm SL (3 specimens), R / V Prof. Mesyatzev, Cruise 7, trawl 11,14°51S 86°49’E, 1760 m, 19 March 1979; ZMMGU 15175 , 156– 182 mm SL (3 specimens), R / V Prof. Mesyatzev, Cruise 7, trawl 12, 14°42’S 86°49’E, 1760 m, 19 March 1979; ZMUC P 2397219, 188 mm SL, R / V Vityaz sta.17-2666, 27°49’S 44°34’E, 1870–1880 m, 6 December 1988.

Diagnosis. Precaudal vertebrae 14–16, 3–5 loin vertebrae (last precaudal vertebrae without ribs); long gill rakers on first gill arch 18–21; pectoral-fin rays 16–18; HL:HD 1.38–1.63; maximal HD:HD through center of eye 1.35–1.70; weak head spines on ethmoidal, interorbital and 5th infraorbital; opercular spine sharp, extruding; opercular flap moderately large; vomer narrow, naked or with few teeth or one row of teeth; palatines narrow with 1–3 rows of teeth; basibranchial tooth patch small, narrow with 1–3 rows of teeth; otolith large, 11.5–14.5 % in HL, with single colliculum; OL:OH = 1.22–1.34; OL:TCL = 2.46–2.92.

Description. Meristics: precaudal vertebrae 14–16, last 3–5 vertebrae without ribs; pectoral-fin rays 18 (16– 18); D/V = 5 (4–5); D/A = 23 (21–25); V/A = 16 (15–17); long gill rakers on lower gill arch 20 (18–21). Gill rakers in holotype on lower first gill arch with five short rakers, followed by a series of 20 long rakers. The lower nine of those intercepted by narrow plate shaped rakers with a single spine pointing inward. Upper gill arch with four short rakers intercepted by four semi long rakers.

Morphometrics: in % of SL: HL 14.4–16.0; maximal HD 9.0–11.2; HD through center of eye 5.9–6.9; bony interorbital width 2.6–3.7; snout length 4.7–5.5; upper jaw length 9.5–10.7; predorsal 16.3–18.1; preanal 28.6–31.7; prepelvic 10.8–12.6; prepectoral 15.4–16.4; pectoral length not measurable. Relations: HL:HD = 1.38–1.63; maximal HD:HD through center of eye 1.35–1.70; HL to snout length 2.78–3.30; preanal to predorsal 1.68–1.94; predorsal to prepectoral 1.00–1.11.

Overall slender fish with long tapering tail, but stout head and moderately long snout. Maximal size of fishes investigated 202 mm SL (holotype 153+ mm). Head with flat or slightly concave dorsal profile, with few weak spines such as ethmoidal, interorbital and 5th infraorbital except; outer preopercular rim sometimes with few broad spines; opercle with small but sharp, extruding spine. Eye moderately small located in strongly asymmetric orbit. Maxilla extending far beyond eye, strongly widened posteriorly; supramaxilla very narrow. Infra-/postorbital and mandibular-preopercular pores very wide. Head with few scales on cheeks only. Opercular flap moderately large, sometimes with ridges. Lateral line not discernable.

Dentition.All teeth tiny and cone-shaped. Vomer v-shaped naked or with up to 3 teeth rows anteriorly; palatines with a narrow dentition patch with 1–3 rows of teeth. Premaxilla tooth patches not fused anteriorly; 5–6 rows. Dentary tooth patches not fused anteriorly; with 6–8 rows. Median basibranchial tooth patch small and narrow with 1–3 rows of teeth.

Otolith morphology (n = 5). Size up to 4.65 mm in length (MNHN 1994-0761) (holotype 2.9 mm); OL in % HL = 11.5–14.5; OL:OH = 1.22–1.34; OH:OT = 2.45–2.75. Otolith oval in shape with all rims regularly curved and smooth and without angles. Inner face flat, with very short sulcus positioned at center of inner face; OL:TCL = 2.46–2.92. Sulcus with shallow, undivided, uniform, oval, small colliculum. Dorsal field very wide, without distinct depression; ventral field smooth. Outer face smooth, convex, with low relief central umbo.

Coloration. Live coloration not known. Color of preserved uniformly black.

Discussion. Tenuicephalus multitrabs differs from T. melampeplus in the smaller head expressed in a lower ratio of HL in % of 14.4–16.0 (vs 16.4–17.2), more long gill rakers (18–21 vs 14–16), presence of week ethmoidal, interorbital, 5th infraorbital and outer preopercular spines (vs no spines) and the large otolith (OL in % HL = 11.5– 14.5 vs 8.5) with a small sulcus (OL:TCL = 2.46–2.92 vs 1.87). It differs from T. squamilabrus n. sp. in the lack of scales on the occiput, opercle and maxilla (vs present), the ratio maximal HD:HD through center of eye of 1.35–1.70 (vs 1.75–1.90), the ratio OL in % HL of 11.5–14.5 (vs 5.0–6.5) and the ratio OL:TCL of 2.46–2.92 (vs 1.94–2.30). Otolith sizes have been shown to vary with living depth and ocean basin ( Wilson 1985), but here all three species share the same distribution and depth range and T. multitrabs and T. squamilabrus n. sp. have even been collected in very close vicinity in the Lagonoy Gulf of the Philippines. Therefore we regard the relatively large size of the otoliths in T. multitrabs in comparison to the two other species as a valid morphological signal and in deed the most secure one to distinguish it from T. squamilabrus n. sp. (see below).

Distribution. Tenuicephalus multitrabs is widely distributed in the Indian Ocean (except for its northern part) and the western Pacific. It occurs at depth between 1000 and 2000 m and has been caught at great distance from the nearest shelf areas in the central Indian Ocean (nearly 2000 km, Fig. 51 ) above the Ninety-East Ridge. In fact the largest number of specimens have been caught over the Ninety-East Ridge, and well above the sea bottom indicating that these fishes might obtain a bathypelagic rather than a benthopelagic life style.

Etymology. From multi (Latin) = many, multi, and trabs (Latin) = club, spar, referring to the many long rakers in this species as compared to T. melampeplus .

Figures

FIGURE 4. Examples of first gill arches. 4A, Porogadus miles ZMUC P2397157, 259 mm SL. 4B, Tenuicephalus multitrabs n. sp. CAS 83066, 156 mm SL. 3C, P. solomonensis ZMUC P771578, 173+ mm SL.

FIGURE 39. Tenuicephalus multitrabs n. sp., holotype, 153+ mm SL, CAS 83066, Laganoy Gulf, Philippines, 1037–1100 m.

FIGURE 40. Tenuicephalus multitrabs n. sp.; 40A–B, holotype, 153+ mm SL, CAS 83066, Laganoy Gulf, Philippines, 1037– 1100 m, head drawings; 40C–D, ZMMGU 15174, 195 mm SL, paratype, 11°31’S, 88°55’E, 1600–1700 m, head drawings; 40E–G, MNHN 1994-0761, paratype, 202 mm SL, 22°06’S, 166°27’E, 1920 –2040 m, otolith (E inner face, F ventral view, G anterior view); 40H–I, CAS 83066, paratype, 156 mm SL, Laganoy Gulf, Philippines, 1037–1100 m, otolith (H inner face, I ventral view); 40J, holotype, 153+ mm SL, CAS 83066, Laganoy Gulf, Philippines, 1037–1100 m, otolith (inner face).

FIGURE 48. Geographic distribution of the species of the genus Tenuicephalus.

FIGURE 51. Depth versus distance from shelf plots for specimens of the genus Tenuicephalus.