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 Author Nielsen, Jørgen G. text Zootaxa 2011 2867 59 66 journal article 10.5281/zenodo.201574 4205abba-b9a9-4aa7-9953-b3a73eaa1d7f 1175-5326 201574 Pseudonus squamiceps Lloyd, 1907 Figs. 1–5 Diplacanthopoma squamiceps Lloyd, 1907 : 10 ( type locality off southeast coast of Arabia, 13°09’N , 46°45’E ). Diplacanthopoma squamiceps : Lloyd 1908 : pl. 42; Lloyd 1909 : 165 ; Menon & Yazdani 1968 : 148 . Cataetyx platycephalus Smith & Radcliffe, 1913: 109 , pl. 16, fig. 1; de Beaufort & Chapman 1951 : 440 , fig. 80. Material examined ( 14 specimens , 76–116 mm SL): USNM 74150 ( holotype of P. platycephalus ), 114 mm SL, female, Molucca Passage, Philippines , 0°37’N , 127°15’E , R/V Albatross, st. 3876, beam trawl, 763 m , 27 Nov. 1909 . USNM 398909 ( paratype of P. platycephalus ), 76 mm SL, off northern Mindanao, Philippines , 8°34’48’’N , 124° 1’24’’E , R/V Albatross, st. 5515, beam trawl, 1281 m , 8 Aug. 1909 . USNM 227191, 108 mm SL, male, Gulf of Aden, 13°5’36’’N , 46°24’42’’E , R/V John Murray, st. 34, Agassiz trawl, 1022 m , 19 Oct. 1933 . BMHN 1939.5.24.1501, 116 mm SL, male, Gulf of Aden, 14°36’6’N, 51°0’18’’E to 14°38’42’’N , 50°57’42’’E , R/V John Murray, st. 184, Agassiz trawl, 1270 m , 4 May 1934 . USNM 226488, 96 mm SL (male) and 92 mm SL (female), off Manila Bay and Lubang Id., Philippines , R/V Coriolis, Nov. 1980 . MNHN 1984-0652, 96–99 mm SL, 2 females , off Luzon Id., Tayabas Bay, 14°1’N , 120°18’E , R/V Coriolis, Musorstom 2 survey, st.49cp4, beam trawl, 183–190 m , 26 Nov. 1980 . ASIZ P 63829 , 107 mm SL, female, off southwestern Taiwan , 22°32’45’’N , 120°5’48’’E , otter trawl, 810 m , 29 Aug. 2002 . ASIZ P 64137 , 106 mm SL, male, off southwestern Taiwan , 22°N, 120°48’E , CD203, otter trawl, 864 m , 29 May 2003 . NMV A 29719-018, 100 mm SL, male, and 76 mm SL, female, off Northwestern Australia , Leveque L27 transect, 14°36’53’’S , 121°19’39’’E to 14°36’15’’S , 121°20’41’’E , R/V Southern Surveyor, beam trawl, 698–705 m , 3 Jul. 2007 . NMV A- 29651-009, 77 mm SL, male, off Northwestern Australia , Barrow L1 transect, 20°59’25’’S , 114°7’54’’E to 20°59’8’’S , 114° 8’24’’E , R/V Southern Surveyor, beam trawl, 700 m , 9 Jun. 2007 . NMV A29679-004, 84 mm SL, female, off Northwestern Australia , Mermaid L24 transect, 16°44’17’’S , 119°15’2’’E to 16°43’48’’S , 119°15’29’’E , R/V Southern Surveyor, beam trawl, 693–698 m , 17 Jun. 2007 . CSIRO H 6593-02, 93 mm SL, female, northwest of Cape Leveque, Western Australia , 14°36’S , 121°20’E , R/V Southern Surveyor, field no. SS0507/147, beam trawl, 705 m , 2 Jul. 2007 . Remarks to material. Additionally three specimens are known from the literature: the two syntypes of P. squamiceps were not available for examination outside ZSI and one of the three specimens caught by the John Murray expedition in the Gulf of Aden seems to be lost. FIGURE 1. Records of Pseudonus squamiceps (● and ․) and P. acutus (˔). The numbers indicate the number of neighbouring stations. FIGURE 2. Pseudonus squamiceps . USNM 227191, SL 108, male. Lateral view. FIGURE 3. Pseudonus squamiceps . USNM 227191, head length 28 mm. Lateral view of head. FIGURE 4. Pseudonus squamiceps . USNM 227191, head length 28 mm. Dorsal view of head. Diagnosis and relationship. Pseudonus squamiceps differs from the only other known species of the genus, P. acutus , by having fewer dorsal fin rays (95–102 vs 101–119), anal fin rays (64–71 vs 74–85) and vertebrae (55–59 vs 61–63); pelvic fins with one ray in each in 14 of the 15 P. squamiceps specimens examined (one specimen with pelvic fin rays absent) vs pelvic fins absent in all six P. acutus specimens examined. Description. The major meristic and morphometric characters are mentioned in Table 2 . Slender body with tapering tail ( Fig. 2 ). Body and gill cover with small, overlapping scales. Indistinct lateral line. Vertical fins joined; origin of dorsal fin above tip of pectorals; origin of anal fin about midpoint of fish; pectoral fins placed below midpoint of body reaching halfway to anus; pelvic fins placed below posterior fourth of gill cover (pelvic fins absent in USNM 226488, SL 96 mm ). Anterior nostril with a low rim close to upper lip, posterior a mere hole in front of eye. Opercle with strong straight or slightly downward-bent spine. Cleithrum with distinct, sharp spine just above pectoral peduncle. Anterior gill arch with two small, spiny knobs on upper branch and lower branch with three long rakers (one specimen with two) and 8–10 small, spiny knobs. Length of gill filaments equal to or larger than long rakers. Two small pseudobranchial filaments. TABLE 2. Meristic and morphometric characters of Pseudonus acutus and s quamiceps.

Standard length in mm	P. squamiceps NWAustralia 5 specimens 76–100	Gulf of Aden 2 specimens 108–116	Philip.+Taiwan 7 specimens 76–114	P. acutus East Pacific 6 specimens 68–121
Meristic characters
Dorsal fin rays	98–102	95–98	96–102	101–119
Caudal fin rays	7–8	8	7–8	8
Anal fin rays	64–71	64–70	65–71	74–85
Pectoral fin rays	21–23	19–20	19–22	21–22
Pelvic fin rays Precaudal vertebrae Total vertebrae	1 16 57–58	1 16 55–59	0–1 15–16 55–58	0 16 61–63
Dorsal fin origin above vertebra no.	9–10	9–11	8–9	10–11
Anal fin origin below dorsal ray no.	28–33	24–30	28–32	25–30
Anal fin origin below vertebra no.	19–21	21	19–21	20–22
Rakers on anterior gill arch	(2)–3 long 8–9 plates	3 long 8–10 plates	3 long 8–10 plates	3 long 8–11 plates
Pseudobranchial filaments Morphometric characters in % of SL	2	2	2	2
Head length	24.0–25.5	26.0–28.5	24.5–27.0	23.0–27.0
Depth at origin of anal fin Upper jaw length Diameter of eye window Interorbital width	11.0–12.5 10.0–11.0 4.3–4.8 2.7–3.0	10.5–13.0 12.0–12.5 4.7–5.4 2.6–2.8	11.5–13.5 10.0–12.0 4.2–5.3 2.1–2.7	11.0–12.0 11.0–13.0 3.9–5.7 2.6–3.2
Postorbital length Heigth of posterior maxilla	14.0–15.5 2.9–3.2	15.0–18.0 3.1–3.7	15.0–17.0 2.8–3.9	14.0–16.0 2.5–2.9
Preanal length	49.5–53	52–61	52–60	50–53
Predorsal length	33.0–34.5	37.0–38.5	32.0–37.5	35.5–37.0
Base of pelvic to anal fin origin	29.0–32.0	30.0–37.5	34.0–40.0	–
Length of pectoral fin Length of pelvic fin	11.0–13.5 7.4–10.5	– -	11.0–14.5 6.7–12.0	10.5–13.5 -

Head pores ( Figs. 3–4 ): One pore in front of each eye, one pore between eyes and three pores behind each eye all of which are large and prominent. Six suborbital pores, five pores in mandibular row and three preopercular pores. Dentition: All teeth are small, pointed and close-set. The boomerang-formed vomer and palatines with 2–4 rows, dentaries with 4–6 irregular rows and premaxillaries with 5–7 irregular rows. Sagittal otolith ( Figs. 5 A–B): Otolith pointed anteriorly and more blunt posteriorly. Dorsal and ventral rim subeven. Sulcus undivided and placed closest to anterior and ventral rim, its length one third of otolith length. Otolith twice as long as high and about five times as long as thick. FIGURE 5. Right sagittal otolith of Pseudonus squamiceps , NMV A 29719-018, SL 100, female: A. Median view, B. Ventral view. Axial skeleton (from radiographs): Number of precaudal vertebrae 15–16. Anterior neural spine about one third the length of second spine. All neural and haemal spines with pointed tips. Neural spines 2–10 depressed. Neural spines 4–11 with enlarged bases. Parapophyses on vertebrae 7–9 to 15–16 . Pleural and epipleural ribs very thin and therefore difficult to count with any certainty. Coloration. Specimens preserved for three years are light brown with blue eyes and greenish lens, brownish branchial cavities and light blue abdomen. Distribution. Known from three separated areas ( Fig.1 ): Gulf of Aden ( 5 specimens ), Philippines and south of Taiwan ( 8 specimens ) and off Northwest Australia ( 5 specimens ). All were caught in bottom trawls at depths between 416 and 1270 m .