Barathronus roulei Nielsen 2019, n.

Barathronus roulei n. sp.

Table 2. Figs. 1, 25

Barathronus parfaiti: Roule, 1916: 18–19; Roule 1919: 73–74.

Barathronus parfaiti (in part.): Roule 1915: 57–58; Grey 1956: 221; Nielsen 1969: 53–57.

Barathronus sp.: Nielsen et al. 1968: 242, 247.

Material examined (1 specimen, SL 100 mm). Holotype: MOM POI-0003655, SL 100 mm, male, Azores, 39°11’N, 30°44’40’’W, RV Princesse-Alice, st. 698, trawl, 1846 m, 18 July 1896.

Diagnosis. Barathronus roulei differs from the other five Barathronus species with a pigmented peritoneum by the following combination of characters: dorsal-fin rays 71, anal-fin rays 66, precaudal vertebrae 34, total vertebrae 82, origin of dorsal fin above vertebra 29, anterior gill arch with 26 long rakers, peritoneum dark, paired bulbs at basis of penis not developed, no ventral flexure of anteriormost vertebrae and vomer with one fang in each side and 2–3 small, pointed teeth in between.

Description. Body compressed with caudal part rather short and loose, transparent skin. Origin of dorsal fin at midpoint of fish and anal fin origin well behind midpoint. Tip of pectorals end halfway to anus and pectoral peduncle as high as long. Pelvic fins end below middle of pectoral fin. Head broad and high with an almost vertical mouth-cleft. Eyes indistinct consisting of a subcircular, dark ring (4 mm in diameter) with a small (0.5 mm) centrally placed and deeper situated dark spot. Nostrils with a low rim placed close together midway between upper lip and eyes. Anterior gill arch with one short and five long rakers on upper branch, one long raker in the angle, and lower branch with 20 long and two short rakers. Gill filaments about 50. Pseudobranch with 2–3 filaments. Histological examination of the gonads showed many spermatocytes and no spermatozoa indicating an unripe male, which corresponds well with the only 1 mm long penis placed in a thick-walled urogenital hood. Otoliths dissolved.

Sensory papillae. All very small with 12–14 papillae in lateral midline on caudal part; from about anus it forks into a dorsal and ventral branch the latter with 8–10 papillae which ascend near tip of pectoral fin reaching dorsal branch behind gill slit. Dorsal branch consists of 20–25 papillae arranged in an irregular row. Head with indistinct sensory canals. Four supratemporal papillae, preopercular-mandibular canal with 3–4 papillae on preopercular and 12 prolonged papillae on mandible.

Dentition. Premaxillary with small, pointed teeth arranged in 3–4 rows anteriorly decreasing to one posteriorad. Vomer with a large fang in each side and a few smaller, pointed teeth in between. Dentaries with numerous small teeth on anterior third, middle third with 3–4 large, recurvated fangs and posterior third edentate.

Vertebral column (from radiographs). Number of precaudal vertebrae 34. Anterior neural spine the longest and thereafter length gradually decreases to caudal fin. Haemal spines and arches similar in form and length to corresponding neural ones. Thin pleural ribs on 3-8 vertebrae and parapophyses on precaudal vertebrae 9–34.

Coloration (Fig. 25). Roule (1919) described the color of the newly caught specimen as: “The body has a uniform greyish color. Around the jaws and eyes the specimen is somewhat more brown-yellow and darkish. The fins are bluish with the fin bases ochrous”. After 72 years of preservation the body is brownish gray and the peritoneum dark.

Comparisons. Barathronus roulei is most similar to B. bicolo r, but differs by the higher number of anal fin rays (66 vs 53–61) and vertebrae (82 vs 69–73), fewer long rakers on anterior gill arch (26 vs 28–35) and origin of dorsal fin above vertebra no. (29 vs 22–28). Already Nybelin (1957: 314) had indicated the similarity to B. bicolor. As shown by the list of synonyms above and by the list in connection with B. parfaiti the present specimen has often been referred to B. parfaiti.

Distribution (Fig. 1). Trawled on a depth of 1846 meters off the Azores.

Ethymology. Named after the French ichthyologist, Louis Roule.