Parasciadonus brevibrachium Nielsen, 1984

Nielsen, Jørgen G., 2016, Revision of the genera Meteoria and Parasciadonus (Bythitidae) with a new Atlantic, abyssal species of Meteoria, Cybium 40 (3), pp. 215-223 : 222-223

Parasciadonus brevibrachium Nielsen, 1984

(Tab. II, Figs 1 , 8 , 9 )

Parasciadonus brevibrachium Nielsen, 1984: 40 (type locality Central Atlantic ).

Parasciadonus brevibrachium : Nielsen et al., 1999: 141.

Material examined

Holotype. – MNHN 1979-228 , SL 72 mm, female, Central Atlantic , 10°59’N, 45°15’W, Biovema, st. A ( CP 02 ), bottom trawl, 5073 m, 14 Nov. 1977.

Diagnosis As of genus.

Description

The principal meristic and morphometric characters are shown in table II. Body elongate and compressed. Skin loose, scaleless and transparent. Minute skinflaps (12-19) along lateral line on both sides of body. Head about double as wide as body with a flat profile. Mouth opening horizontal. Lower jaw distinctly protruding. Small eyes deep-set, placed well behind posterior end of upper jaw. Nostrils midway between upper lip and eyes. No opercular spine. Dorsal fin origin at midpoint and anal fin origin well behind midpoint of fish. Pectoral peduncle short, as high as long. Pelvic fins absent. Figure 9 shows the presence of 15 minute rakers on the anterior gill arch and a few poorly developed gill filaments; both rakers and filaments more developed on 2 nd- 4 th gill arches. Pseudobranchial filaments not observed.

Gonads. – A histological examination of part of the 12 mm long ovaries (16.5% SL) shows many eggs of different sixes (up to 0.5 mm). No embryos, but numerous spermatozoa observed in the ovarian tissue. A distinct genital hood. Claspers not developed.

Axial skeleton (from radiographs). – Number of precaudal vertebrae 50. Anterior neural spine equal in length to the following spines. Ribs and parapophyses absent. Centrum of posterior precaudal vertebra twice as high as long.

Dentition. – Anterior half of dentaries with 2-3 irregular rows of small, sharp, retrorse teeth near symphysis with longest teeth in inner row and further back teeth in a single row; posterior half of dentaries edentate. Similar dentition on premaxillaries. Palatines edentate. Vomer with a few very small, blunt teeth.

Otolith. – Now dissolved, but old radiographs show that the sagittal otoliths were about 1 mm in length.

Coloration. – General colour yellowish. Scattered, black pigment on peritoneum and in dorsal midline. Eyes black.

Distribution

Parasciadonus brevibrachium is known from one specimen caught in the Central Atlantic in a bottom trawl at a depth of 5073 m .

Remarks

The fact that the four species treated in this paper are known from seven specimens only, shows how rarely they are caught, but it is difficult to judge how rare the species actually are considering how few abyssal trawl hauls that have been undertaken. In the last decades the number of hauls has decreased even further while the number of photos from abyssal depths has increased considerably. Unfortunately, quite often a specific identification of the specimens shown on the photos is not possible. More sampling is required in the deep sea!

Acknowledgments. – I wish to thank the following persons for providing data and/or material: Hans Peter Dahlgren (NHMG), Guy Duhamel (MNHN), Irina Eidus (ZMH) , Eric Hilton (VIMS), Sarah Huber (VIMS), James Maclaine (BMNH), Ralf Thiel (ZMH), Jeff Williams (USNM). Marcus Krag (ZMUC) provided the photos.

Figures

Figure 1. – Records of species of Meteoria and Parasciadonus.

Figure 8. – Parasciadonus brevibrachium, MNNH 1979-228, holo- type, female, SL 72 mm. A: Drawing; B: Photo after 38 years of preservation.

Figure 9. – Parasciadonus brevibrachium, MNNH 1979-228, holo- type: anterior, left gill arch.