Pseudonus acutus Garman , 1899

Nielsen, Jørgen G., 2011, Revision of the bathyal fish genus Pseudonus (Teleostei, Bythitidae); P. s q u a m i c e p s a senior synonym of P. platycephalus, new to Australian waters, Zootaxa 2867, pp. 59-66 : 64-66

Pseudonus acutus Garman, 1899

Figs. 1 , 6–9

Pseudonus acutus Garman, 1899: 169 , pl. XXXIII (type locality off Galapagos Is., 0°4’S, 90°24’30’’W). Pseudonus acutus: Nielsen et al. 1999: 107 ; Nielsen & Nishioka 2009: 201.

Material examined (6 specimens, 68–121 mm SL): Holotype: MCZ 28630, 69 mm SL, female, off Galapagos Is., 0°04’S, 90°24’30’’W, R/V Blake, st. 3407, bottom trawl, 1620 m, 3 Apr. 1891.

Non-types: ZMUC P 771516-1518, 68– 77 mm SL, 3 females, Gulf of Panama, 7°22’N, 79°32’W, R/V Galathea, st. 739, bottom trawl, 915–975 m, 15 May 1952. - HUMZ 174426, 77 mm SL, male, off northern Peru, 4°6.3’S, 81°20.1’W, R/V Shinkai-maru, st. NET47, bottom trawl, 981–1093 m, 8 May 2000. – HUMZ 175107, 121 mm, female, off northern Peru, 8°11.9’S, 80° 11.9W, R/V Shinkai-maru, st. NET38, bottom trawl, 1061–1105 m, 27 Apr. 2000.

Diagnosis and relationship. See under P. squamiceps (p.?).

Description. The major meristic and morphometric characters are mentioned in Table 2 . Body slender with pointed head and tapering tail ( Fig. 6 ). Preopercle and body with small, overlapping scales. Lateral line indistinct. Vertical fins joined; origin of dorsal fin above tip of pectoral fin; origin of anal fin at about midpoint of fish; pectoral fin placed below midline of body reaching about halfway to anus; pelvic fins absent. Anterior nostril close to upper lip and posterior near eye both a mere hole. Diameter of eye window equal to length of snout. Upper jaw ending somewhat posterior to hind margin of eye. Opercle with strong, slightly upward-bent spine. Cleithrum with distinct, sharp spine just above pectoral peduncle. Anterior gill arch with three small, spiny knobs on upper branch and lower branch with three long rakers and 8–11 small, spiny knobs. Length of gill filaments shorter than long rakers. Two small pseudobranchial filaments.

Head pores ( Figs. 7–8 ): One pore in front of each eye, one pore between eyes and three pores behind each eye all of which are large and distinct. Six suborbital pores, five mandibular pores and three preopercular pores.

Dentition: All teeth are small, pointed and retrorse. The boomerang-formed vomer and palatines with 2–3 rows and dentaries and premaxilaries with about five rows.

Sagittal otolith ( Figs. 9 A–B): Otolith with both anterior and posterior end forming an angle. Sulcus undivided and placed centrally, its length 1/4–1/3 of otolith length. Otolith length twice its height and four times as long as thick.

Axial skeleton (from radiographs): Number of precaudal vertebrae 16. Anterior neural spine half the length of second spine. All neural and haemal spines with pointed tips. Neural spines 3–8 somewhat depressed. Neural spines 6–13 with enlarged bases. Parapophyses on vertebrae 9–16. Thin pleural ribs on vertebrae 3–8. Epipleural ribs indistinct.

Coloration. Specimens preserved for ten years have a light brown body, a mainly brown head with blue eyes and a white lens and a bluish abdomen.

Distribution. The five additional specimens were caught off Equador and northern Peru not far from the type locality ( Fig. 1 ). All specimens were taken in bottom trawls at depths between 915 and 1620 m.

Figures

FIGURE 1. Records of Pseudonus squamiceps (● and ․) and P. acutus (˔). The numbers indicate the number of neighbouring stations.

FIGURE 6. Pseudonus acutus. ZMUC P 771516, SL 77, female. Lateral view.

FIGURE 7. Pseudonus acutus. ZMUC P 771516, head length 19 mm. Lateral view of head.

FIGURE 8. Pseudonus acutus. ZMUC P 771516, head length 19 mm. Dorsal view of head.

FIGURE 9. Right sagittal otolith of Pseudonus acutus, HUMZ 175107, SL 121, female: A. Median view, B. Ventral view.