Sciadonus longiventralis, Nielsen, 2018

Nielsen, Jørgen G., 2018, Revision of the cosmopolitan deep-sea genus Sciadonus (Teleostei, Bythitidae) with two new species, Cybium 42 (2), pp. 177-187 : 182

Sciadonus longiventralis n. sp.

( Tab. I, Figs 1 , 6-7 )

Material examined (1 specimen, SL 70 mm)

Holotype. NMV A5672 , SL 70 mm, male, off New South Wales , 35°0.00’S- 34°54.42’S, 151°16.30’E- 151°13.36’E, R / V Franklin, st. CSIROFR5/86, 5 m otter trawl, 1100 m, 15 Jul. 1986.

Diagnosis

Sciadonus longiventralis is long, slender and compressed. Mouth horizontal with protruding lower jaw. A pair of distinct tissue flaps anteriorly on lower jaw. No black pigment spots seen through transparent skin. Dorsal fin rays 87, anal fin rays 52, pectoral fin rays 14, precaudal vertebrae 39 and total vertebrae 80. Pelvic fin rays long (3.5% SL) and predorsal length 28.5% SL.

Description

The principal meristic and morphometric characters are shown in table I. Body slender and compressed with loose, scaleless, transparent skin showing the inner organs ( Fig. 6 ). Anterior nostril with skin-flap, posterior a mere hole. Mouth horizontal with protruding lower jaw. A distinct pair of tissue flaps on tip of lower jaw ( Fig. 7 ). Small, black, deep-set eyes placed above middle of upper jaw. Opercular spine absent. Otolith dissolved. Origin of dorsal fin above tip of pectoral fin. Origin of anal fin well behind midpoint of fish. Vertical fins joined. Pectoral peduncle three times as long as high. Pelvic fin rays thin and the longest (3.5% SL) among the 34 Sciadonus specimens examined for this revision. Anterior gill arch with 15 small rakers and short filaments. Second and third arches with small rakers and 2-3 times as long filaments and fourth arch without filaments. Pseudobranchial filaments not observed. A well-developed, rather flat urogenital hood with a wing-like extension distally on each side of the hood that ends in a penis-like prolongation. Length of distinct testes 11 mm.

Figures

Figure 1. – Records of Sciadonus species.

Figure 6. – Sciadonus longiventralis n. sp. NMV A 5672, holotype, male, SL 70 mm.

Figure 7. – Sciadonus longiventralis: Ventral view of head. MNV A 5672, holotype, male, SL 70 mm. a: tissue flaps, b: ventral fins.