Nybelinella erikssoni Nybelin 1957

Nybelinella erikssoni (Nybelin, 1957)

Table 1, Figs. 1–8

Barathronus erikssoni Nybelin, 1957: 308, pl. VII (type locality: tropical East Atlantic); Marshall 1960: 111; Munk 1965: 27; Munk 1966: 37; Nielsen et al. 1968: 242.

Nybelinella erikssoni: Nielsen 1972: 53; Cohen & Nielsen 1978: 62; Haedrich & Merrett 1988: 1336; Merrett 1992: 8; Nielsen et al. 1999: 140; Herring 2002: 174, 185.

Nybelinia erikssoni: Nielsen 1969: 23, fig. 12.

Material examined (22 specimens, SL 30-85 mm): Holotype: NHMG Pi. 1743, SL 75 mm, female, tropical East Atlantic, 01°03’N, 18°40’W, Swedish Deep-Sea Exped. st. 342, bottom trawl, 5250–5300 m, 16 July 1948. Nontypes: ZMUC P77455, SL 70 mm, male, north of Madagascar, 05°25’S, 47°09’E, R/ V Galathea, st. 274, herring otter trawl, 4820 m, 10 Mar. 1951. ZMH 26054, SL 57 mm, female, off NW Spain, 42°38’N, 13°36’W, R/ V Meteor, st. 24, Agassiz Trawl, 5000 m, 16 Sep. 1968. MNHN 1979-231, SL 55 mm, male, Angola Basin, 27°00’S, 01°06’E, Campagne Walvis, st. C (CP10), bottom trawl, 5211 m, 7 Jan. 1979. ZMUC P77706 (former VIMS 05711), SL 78, female, Bahamas, 26°03.3’-10.2’N, 74°03.2’-02.1’W, R/ V Columbus Iselin, cr. CI-8007, st. C-027, 45’semi-balloon trawl, 5065 m, 10 Sep. 1980. BMNH 2016.7.29.1, SL 30 mm, male, SW of Azores Isls., 34°58’6’’N, 32°56’30’’W, R/V Discovery, st. 10379#37, 2960– 2985 m, 16 June 1981. VIMS 34749, SL 73 mm, male, Bahamas, 23°02’N, 68°24’W, R/ V Columbus Iselin, st. D-018, 45’ otter trawl, 5303–5387 m, 25 Nov.1981. VIMS 0 6618, SL 55 mm, female, Venezuela Basin, 13°51.8’-45.5’N, 67°52.4’-46.2’W, R/ V Bartlett, cr. 1301-82, st. E-065, 45’ otter trawl, 5000 m, 9 Nov. 1981. VIMS 0 6 619, SL 60, male, Venezuelan Basin, 14°16.7’-21.9’N, 67°06.2’- 66°58.4’W, R/ V Bartlett, cr. 1301-82, st. E-096, 45’otter trawl, 5011 m, 30 Nov. / 1 Dec. 1981. ZMH 121802, SL 83 mm, female, off NW Spain, 45°55’N, 17°10’W, R/ V Walther Herwig 2, Agassiz Trawl, 4640 m, 27 Apr. 1984. ZMH 119263, SL 76 mm, male, off NW Spain, 42°23'N, 14°31'W, R/ V Walther Herwig 2, Agassiz Trawl, 5260 m, 3 May 1984. BMNH 2016.7.29.2-3, 2 specimens, SL 85 mm (female) and SL 39 mm (unripe), north of Madeira, 34°45’42’’N, 18°30’W, R/ V Discovery, st. 11134#1, OTSB 14, 4790– 4880 m, 10 June 1984. BMNH 2016.7.29.8, SL 36 mm, male, SW of Madeira, 31°12’48’’N, 25°18’18’’W, R/ V Discovery, st. 11261#50, OTSB, 5440 m, 2 July 1985. BMNH 2016.7.29.4-7, 4 specimens, SL 45–68 mm, SW of Madeira, 31°7’N, 25°5’12’’W, R/ V Discovery, st. 11261#44, OTSB, 5440 m, 1 Aug. 1985. BMNH 2016.7.29.9, SL 60 mm, SW of Madeira, 31°12’36’’N, 25°12’30’’W, R/ V Discovery, st. 11261#52, OTSB, 5440 m, 3 Aug. 1985. BMNH 1994.5.9.7, SL 62 mm, female, SW of Madeira, 20°55’58’’N, 31°11’29’’W, R/ V Discovery, st. 12600#66, OTSB, 4500–4610m, 16 Oct. 1993. BMNH 2016.7.29.10, SL 50 mm, female, off Madeira, 35°39’30’’N, 13°41’20’’W, R/ V Challenger, st. 53603#2, OTSB, 4855-4861 m, 29 Sep. 1995.

Tentatively referred specimen: BMNH 2016.7.29.12, SL 57+ mm, ripe female, off Western Sahara, 25°33’36’’N, 16°40’6’’W, R/V Discovery, st. 8682# 5, 150 cm sledge, 3000 m, 7 Feb. 1975. A part of the caudal fin is missing so many of the meristic and morphometric characters are unobtainable. The remaining characters are typical for N. erikssoni except for the following: pectoral-fin rays 19 (vs. 23–27 in N. erikssoni) and rakers on anterior gill arch 20 (vs. 23–27) of which two are slightly prolonged (vs. 5–8). Additional material may settle the taxonomic position of the present specimen.

Remarks on material. Ten of the 22 specimens here examined have been mentioned earlier in the literature, but for only three of these (NHMG Pi.1743 (holotype), ZMUC P77455 and ZMH 26054) a description was published while seven were merely listed by Merrett (1992) as caught abyssally in the eastern North Atlantic.

Diagnosis. Nybelinella erikssoni is long, slender and compressed. Dorsal fin with 79–92 rays, anal fin with 51–57 rays and pectoral fin with 23–27 rays. Precaudal vertebrae 37–42, total vertebrae 75–79. Origin of anal fin below dorsal fin no. 29–40. Totally 23–27 small rakers on anterior gill arch with 3–4 on upper branch and lower branch with the dorsal 5–8 rakers slightly longer than the rest. Gill filaments very small. Predorsal 39.5–46.5% SL and preanal 58–64% SL.

Comparisons. Nybelinella erikssoni differs from N. brevianalis by having more anal fin rays (51–57 vs. 45), totally 23–27 rakers on anterior gill arch (vs. 20), 5–8 slightly prolonged rakers dorsally on lower branch of anterior gill arch (vs. none) and preanal length shorter (58–64% SL vs. 73% SL). From N. brevidorsalis it differs by having more dorsal fin rays (79–92 vs. 70), origin of anal fin below dorsal fin no. 29–40 (vs. 19) and predorsal length 39.5– 46.5 % SL (vs. 52).

Description. The principal meristic and morphometric characters are shown in Table 1 and for a thorough description of the holotype and ZMUC P77455 see Nielsen (1969: 23). Body slender and head higher and broader than body. Skin loose, transparent and scaleless. Mouth oblique with protruding lower jaw. Eyes deep-set with a centrally placed pigmented part surrounded by a narrow black ring (diameter 1.5–2.3 % SL). Eyes of smaller specimens more densely pigmented and thus more distinct. Nostrils and head pores difficult to observe due to torn skin. Origin of dorsal fin well in front of midpoint of fish and origin of anal fin posterior to midpoint. One short ray in each pelvic fin placed below basis of pectoral fin. Anterior gill arch with 3–4 minute rakers on upper branch and lower branch with 20–24 small rakers of which the upper 5-8 are longer than the rest. Gill filaments extremely small (Fig. 3). Small, semi-spherical sagittal otoliths twice as long as thick and with a centrally placed, undivided sulcus (Fig. 4). Six of the females are ripe with dark brown eggs about 1 mm in diameter and two of them with free, about 10 mm long embryos (Fig. 5). Females with a pair of claspers posteriorly on urogenital sinus; median fold rarely intact (Fig. 6). Males with well-developed urogenital hood ventrally covering penis; claspers not developed (Fig. 7).

Axial skeleton (Fig. 8). Number of precaudal vertebrae 37–42. Neural spine of anterior vertebra the longest with spine-length decreasing posteriorad. Parapophyses and ribs not developed except for a few specimens with a weak ventral process on the posterior 1–2 precaudal vertebral centra. All vertebral centra are almost rectrangular in lateral view. In a 30 mm SL specimen the highest precaudal vertebral centrum is seven times higher than long, in a 57 mm SL it is three times higher than long and in a 85 mm SL it is twice as high as long.

Dentition. All teeth are very small, pointed and most of them retrorse. Premaxillaries and dentaries with 3-4 rows near the symphysis decreasing to one row further back and with the posterior third edentate. Vomer with 5–15 teeth medially and a few specimens with scattered teeth on the wings. Palatines edentate.

Coloration. Head and body uniformly brown to light-brown. Comparison with photos of newly caught specimens shows that not much bleaching has taken place. Eye and surrounding ring black.

Distribution (Fig. 1). Nybelinella erikssoni is caught in the North Atlantic except for two specimens from the southeastern Atlantic and north of Madagascar. They were caught in bottom fishing gear at depths between 2960 and 5440 m.