Nybelinella brevianalis, Nielsen, Jørgen G., 2017

Nielsen, Jørgen G., 2017, Revision of the genus Nybelinella (Teleostei, Bythitidae) with a new Atlantic, abyssal species, Zootaxa 4247 (1), pp. 45-54 : 51

Nybelinella brevianalis n. sp.

Table 1 , Figs. 9–10

Material examined (1 specimen, SL 62 mm). Holotype: BMNH 2016.7 .29.11, SL 62 mm, female, west of Madeira , 31°14.9’N, 27°7.5’W, R/ V Discovery, st. 12174#31, OTSB 14, 4914– 4938 m, 20 Aug. 1990.

Diagnosis. Nybelinella brevianalis is long, slender and compressed. Dorsal fin with 81 rays, anal fin with 45 rays and pectoral fins with 25 rays. Totally 76 (42 +3 4) vertebrae. Origin of anal fin below dorsal fin no. 33. Upper branch of anterior gill arch without rakers and lower branch with 20 equally sized, small rakers. Small teeth on vomer. All neural and haemal spines ovate-formed (see note to Key to Species). Predorsal 44.0% SL and preanal 73% SL.

Comparisons. Nybelinella brevianalis differs from N. brevidorsalis and N. erikssoni by having fewer anal fin rays (45 vs. 50-57), no rakers on epibranchials (rakers present) and all neural and haemal spines ovate-formed (vs. all spines thin and pointed). From N. brevidorsalis it differs furthermore by having more dorsal fin rays (81 vs. 70), shorter predorsal length (44.0 vs. 52% SL) and origin of anal fin below dorsal fin ray no. 33 (vs. 19) and from N. erikssoni it differs by a longer preanal length (73% vs. 58–64 % SL).

Description. The principal meristic and morphomorphic characters are shown in Table 1 . Body elongate and slender. Head higher and broader than body. Skin loose, transparent and without scales. Lower jaw slightly protruding. Eyes small and deep-set with a centrally placed pigmented part (0.4 mm in diameter) surrounded by a narrow, black ring (1 mm in diameter). Nostrils and head pores very difficult to observe due to torn skin. Vertical fins joined. Origin of dorsal fin well in front of midpoint of fish. Origin of anal fin far behind midpoint of fish (preanal length 73% SL). Pelvic fins, with one short ray in each, placed below basis of pectoral fins. Anterior gill arch without rakers on upper branch and lower branch with 20 equally sized, small rakers all provided with small denticles. Gill filaments extremely small. Length of distended ovaries 17 mm. Many fertilized eggs (1 mm in diameter) and several free embryos (10 mm long). Urogenital hood ends in a pair of torn claspers.

Axial skeleton ( Fig. 10 ). Number of precaudal vertebrae 42. All neural and haemal spines ovate-formed. Parapophyses and ribs not developed. The two vertebrae just in front of the anterior vertebra with an ovate haemal spine are provided with a short, thin ventral process; they are counted as the two posteriormost precaudal vertebrae. All vertebral centra almost rectangular in lateral view, twice as high as long.

Dentition. All teeth small and pointed, some retrorse. Premaxillaries and dentaries with 3–4 rows anteriorly decreasing to one row posteriorly. Vomer with median patch of about 15 teeth. Palatines edentate.

Coloration. After 26 years of preservation the fish is brownish except for the deep-set eyes which appear as a thin, black ring with a black center. The white liver and dark brown, ripe eggs are seen through the transparent peritoneum.

Distribution ( Fig. 1 ). Known from one specimen trawled at abyssal depth (4914–4938 m) west of Madeira in the Northeast Atlantic Ocean.

Etymology. The specific name, brevianalis , refers to the short anal fin.

Figures

FIGURE 1. Records of Nybelinella species.

FIGURE 9. Nybelinella brevianalis: BMNH 2016.7. 29.11, holotype, female, SL 62 mm.

FIGURE 10. Radiograph of Nybelinella brevianalis: BMNH 2016.7. 29.11, holotype, SL 62 mm.