Leucicorus atlanticus Nielsen 1975

Leucicorus atlanticus Nielsen, 1975

Table 1, Figs. 1A, 2C, 3A–D, 5

Leucicorus atlanticus Nielsen, 1975: 113, fig. 1.

Leucicorus atlanticus: Hureau & Nielsen 1981: 16; Nielsen & Møller 2008: 29.

Material examined (22 specimens, SL 48–240 mm).

Holotype: ZMUC P 771813, 154 mm SL, male, Cayman Trench, 19°00’N, 80°38’W, R / V Akademik Kurchatov, cr. 14, st. 1243, Sigsbee trawl, 6400–6800 m, 16. Mar. 1973.

Paratypes (17 specimens): UF 230276 (former UMML 30276), 205 mm SL, female, Puerto Rico Trench, 22°02’N, 65°10’W, R / V Pillsbury, st. 1374, 41’ otter trawl, 5541–5563 m, 2 July 1971. IORAS 02295, 110–151 mm SL and ZMUC P 77575, 154 mm SL, female, Cayman Trench, 18°59’N, 80°30’W, R / V Akademik Kurchatov, cr. 14, st. 1242-A, Sigsbee trawl, 6800 m, 20 Mar. 1973. IORAS 7 specimens not catalogued (specimens missing), 48–139 mm SL and ZMUC P 77585, 125 mm SL, Cayman Trench, 19°05’N, 80°29’N, R / V Akademik Kurchatov, st. cr. 14, 1259, Sigsbee trawl, 6800– 6500 m, 22 Mar. 1973. IORAS 02296, 2 specimens, 79–152 mm SL and ZMUC P77586, 78 mm SL, Cayman Trench, 19°44’N, 76°12’W, R / V Akademik Kurchatov, cr. 14, st. 1266, Sigsbee trawl, 5900–6300 m, 24 Mar. 1973. IORAS 02297,120 + mm SL, Cayman Trench, 19°38’N, 76°40’W, R / V Akademik Kurchatov, cr. 14, st. 1267 Sigsbee trawl, 6740–6760 m, 25 Mar. 1973. IORAS not catalogued (specimen missing), 135 mm SL, Yucatan Trench, 20°08’N, 84°30’W, R / V Akademik Kurchatov, cr. 14, st. 1272, Sigsby trawl, 4580 m, 28 Mar. 1973.

Additional material: MNHN 1979–689, 224 mm SL, Northeast Atlantic Ocean, 10°46.23’N, 42°40.41’W, Campagne Biovema, st. B, benthic trawl, 5100 m, 19 Nov. 1977. VIMS 6857, 183 mm SL, female, Silver Abyssal Plain, 23°20–22.5’N, 68°23–29.4’W, R / V Columbus Iselin, cr. CI-8123, st. D018, 45’ OT, 5303–5387 m, 25 May 1981. BMNH 2020.11.26.2, 240 mm SL, female, Northeast Atlantic Ocean, 38 ° 00’N, 11°32.7’W, R / V Discovery, st. 11911#7, OTSB, 5035 m, 26 Sep. 1989. ZMUC P771571, 87 mm SL, unripe, Solomon Sea, 7°49.4’S, 156°02.8’E, Galathea 3 exp., st. 061228-01, 1.2 m Agassiz trawl, 4350–4450 m, 2 Dec. 2006.

Diagnosis. Dorsal fin rays 82–94, much reduced squamation on preopercle and opercle and occiput almost naked; 18–20 scale rows on trunk above beginning of anal fin. Black eye comparatively small (10–13.5% HL), without or minute lens <10%. Otolith roundish, massive, OL:OH = 1.2–1.55, inner face flat, outer face strongly convex.

Comparison. L. atlanticus is most similar to L. gerringerae by the number of vertebrae and anal fin rays. They differ by the reduced squamation of the occiput in L. atlanticus and in the anal-fin origin placed below dorsal fin rays 15–18 vs 19–21 in L. gerringerae. It further differs in the lower number of transversal scales (18–20 vs 25), more compressed otolith (OL:OH = 1.2–1.55 vs 1.62) with the inner face flat and the outer face strongly convex (vs inner face of otolith convex and outer face slightly convex or flat). It differs from L. lentibus by having fewer dorsal-fin (82–94 vs. 105) and anal-fin (68–80 vs. 87) rays, as well as minute or absent eye lenses (0–10% of black eye vs 57%).

Description. The principal meristic and morphometric characters are shown in Table 1. Body compressed and elongate with tapering tail. Head broad and somewhat depressed with thin fragile bones. Scales often missing, but scale-pockets show a fully scaled body with about 18 to 20 scales transversely across trunk above beginning of anal fin. Head with scaleless occiput and a few scales on opercle and preopercle. Anterior nostril situated midway between upper lip and posterior nostril. Snout equal in length to horizontal orbit. Horizontal length of orbit twice as long as high; lens poorly developed (<10% of diameter of black eye) or absent. Upper jaw ends just below posterior margin of orbit. Opercular spine thin and pointed, almost covered by skin. Upper branch of anterior gill arch with 4–5 knob-like and one long developed raker, a long developed raker in the angle and lower branch with 8–10 long developed and 5–7 knob-like rakers or, 9–12 long developed rakers and 18–21 rakers of both types in total. 1–3 pseudobranchial filaments.

Otolith (Fig. 3A–D). Moderately large otoliths up to 6.2 mm in length (holotype = 5.8 mm) with oval to round shape (otolith length: height = 1.20–1.55, mostly <1.3). Ventral rim regularly curved; dorsal rim variable, broadly rounded or with broad, obtuse, pre- to mediodorsal angle; anterior and posterior rims rounded. Inner face flat, outer face strongly convex; otolith height: thickness = 1.75–2.2. Sulcus horizontal, shallow, short, with single well-defined colliculum; otolith length: sulcus length = 2.52–2.93; sulcus length: height = 2.0–2.5. Ventral furrow variably expressed, mostly wide and weak; no distinct dorsal depression.

Distribution (Fig. 5). Known from eight localities in the West Indies (19 specimens from 4580–6800 m), two localities in the Northeast Atlantic Ocean (two specimens from 5035–5100 m) and one location from the Solomon Sea, SW Pacific (4350–4450 m). Leucicorus atlanticus is the deepest living species in the genus.