Sciadonus jonassoni ( Nybelin, 1957 )

Nielsen, Jørgen G., 2018, Revision of the cosmopolitan deep-sea genus Sciadonus (Teleostei, Bythitidae) with two new species, Cybium 42 (2), pp. 177-187 : 181

Sciadonus jonassoni ( Nybelin, 1957)

( Tab. I, Figs 1 , 4-5 )

Leucochlamys jonassoni Nybelin, 1957: 311 (type locality south of Cape Verde Islands ).

Leucochlamys jonassoni : Nielsen, 1969: 73; Haedrich and Merrett, 1988: 1336; Nielsen et al., 1999: 142; Nielsen, 2016a: 1956.

Material examined (7 specimens, SL 35-51 mm)

Holotype. NHMG Pi. ex. 1745, SL 38 mm, female, south of Cape Verde Islands , 9°38’N, 26°20’W- 9°50’N, 26°30’W, Swedish Deep-Sea Expedition, st. 329, bottom trawl, 5600- 5610 m, 3 Jul. 1948.

Non-type: UF 226945 , SL 37-51 mm, 2 males, off Trinidad and Tobago, 11°30’N, 60°15’W , R / V Pillsbury , st. PIL844, bottom trawl, 1464-1848 m, 1 Jul. 1969 . ZMUC P77707 (former VIMS 05712 ), 35 mm, female, Bahamas, 26°04.0’-10.6’N, 74°03.2’-02.1’W , R / V Columbus Iselin , cr. CI-8007, st. CO27, 45’ otter trawl, 5114- 5049 m, 11 Sep. 1980 . BMNH 2017.3.17.1-2, SL 37-38 mm, 2 females, 31°06’N, 25°03’42’’W , R / V Discovery , st. 11261#58, semi-balloon otter trawl, 5440 m, 4 Jul. 1985 . BMNH 2017.3 .17.3, SL 37 mm, male, sw of Madeira , 31°13’18’’N, 25°14’24’’W , R / V Discovery , st. 11262 #17, bottom trawl, 5432 m, 17 Jul. 1985 .

Diagnosis

Sciadonus jonassoni is slender and compressed. It is a small species with fully ripe females 37 mm in SL and known up to 51 mm SL. Many, small, black pigment spots seen along body midline, along dorsal edge of body and at base of anal fin. Dorsal fin with 68-80 rays, anal fin with 38-49 rays, pectoral fin with 9-10 rays, precaudal vertebrae 35-43, total vertebrae 65-75. Origin of anal fin below dorsal fin rays 27-38. Head length 14.5-20.5% SL. Tissue flaps anteriorly on lower jaw in present or absent.

Description

The principal meristic and morphometric characters are shown in table I; for a more detailed description of the holotype see Nielsen (1969: 73). Body slender and compressed with loose, transparent, scale less skin. Mouth almost horizontal with protruding lower jaw. Deep-set, tiny, black eyes placed above middle of upper jaw. Origin of dorsal fin somewhat behind tip of pectoral fins and origin of anal fin well behind midpoint of fish. Pectoral peduncle 2-3 times as long as high. Anterior gill arch with 13-15 very small rakers, two on upper branch and 11-13 on lower branch. Gill filaments extremely small on anterior arch, somewhat longer on the second and third arches. Males with a small penis covered by a ventrally placed urogenital hood. Females with a pair of almost 1 mm long, slender claspers. All three females apparently ripe with 5- 10 eggs 0.5 mm in diameter. Sagittal otolith 0.3 mm in diameter (measured on radiographs).

Figures

Figure 1. – Records of Sciadonus species.

Figure 4. – Sciadonus jonassoni: NHMG PI. ex. 1745, holotype, female, SL 38 mm (from Nybelin, 1957 – figure reversed).

Figure 5. – Sciadonus jonassoni: ZMUC P77707, female, SL 35 mm. A: Drawing; B: Photo after 37 years of preservation.