Nybelinella brevidorsalis Shcherbachev, 1976

Nielsen, Jørgen G., 2017, Revision of the genus Nybelinella (Teleostei, Bythitidae) with a new Atlantic, abyssal species, Zootaxa 4247 (1), pp. 45-54 : 52-53

Nybelinella brevidorsalis Shcherbachev, 1976

Table 1 , Fig. 11

Nybelinella brevidorsalis Shcherbachev, 1976: 162 (type locality: southeastern Indian Ocean) Nybelinella brevidorsalis: Cohen & Nielsen 1978: 62 ; Nielsen et al. 1999: 140.

Material examined (1 specimen, SL 52 mm). Holotype: ZISP 42297 , SL 52 mm, male, southeastern India Ocean, 12°47’S, 88°54’E, R/ V Vityaz, st. 6744-5, Sigsby trawl, 5160 m, 15 Mar. 1973.

Diagnosis. Nybelinella brevidorsalis is long, slender and compressed with a downward bent head and a slightly protruding lower jaw. Dorsal fin with 70 rays, anal fin with 50 rays and pectoral fins with 27 rays. Totally 72 (37 + 35) vertebrae. Origin of anal fin below dorsal fin ray no. 19. Upper branch of anterior gill arch with short rakers; lower branch with shorter rakers dorsally than ventrally. Palatines and vomer edentate. Predorsal 52% SL and preanal 65% SL.

Comparisons. Nybelinella brevidorsalis differs from N. brevianalis and N. erikssoni by having fewer dorsal fin rays (70 vs. 79–92), fewer vertebrae (72 vs. 75–79), origin of anal fin below dorsal fin ray no. 19 (vs. 29–40), predorsal length 52% SL (vs. 39.5–46.5), no teeth on vomer (vs. small teeth on vomer) and by having longer rakers ventrally on lower branch of anterior gill arch (vs. longer rakers dorsally on lower branch in N. erikssoni and all rakers equal in length in N. brevianalis ). Furthermore, N. brevidorsalis differs from N. brevianalis by having slender neural and haemal spines (vs. ovate-formed spines).

Description. The original description was published in Russian. The present description is based on a translation of the original description and examination of the holotype. The principal meristic and morphometric characters are shown in Table 1 . Body long and slender and head higher and broader than body. Skin loose, transparent and without scales. Lower jaw slightly protruding. Black eyes small and deep-set with a black, surrounding ring. Vertical fins joined. Origin of dorsal fin just behind midpoint of fish. Anal fin origin far behind midpoint (preanal length 65% SL). Anterior gill arch with four short rakers on upper branch and lower branch with seven short followed by 11 somewhat longer rakers on the lower part. Gill filaments very short. A radiograph shows a pair of sagittal otoliths 0.2 mm in diameter. Penis covered ventrally by well-developed urogenital hood.

Axial skeleton (from radiographs). Number of precaudal vertebrae 37. All neural and haemal spines thin and pointed. Anterior neural spine longest and the spines gradually decreasing in length posteriorad. Parapophyses and ribs not developed. All vertebral centra almost rectangular in lateral view, being twice as high as long.

Dentition. Teeth generally poorly developed. Palatines and vomer edentate. Premaxillaries and dentaries with small, pointed teeth.

Coloration. After two years in formalin the specimen was yellowish with small cinnamon-brown pigment spots on body and at base of pectoral fin rays. A black ring surrounds the black eyes.

Distribution ( Fig. 1 ). Nybelinella brevidorsalis is known from one specimen trawled at abyssal depth (5160 m) in the southeastern Indian Ocean.

Figures

FIGURE 1. Records of Nybelinella species.

FIGURE 11. Nybelinella brevidorsalis: ZISP 42297, holotype, male, SL 52 mm.