Pseudonus 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 : 59-60

Pseudonus Garman, 1899

Type species. Pseudonus acutus Garman, 1899 by monotypy. Type locality off Galapagos Isls.

Diagnosis. A viviparous genus with depressed, partly naked head; eyes dorsolaterally directed; head pores large with a prominent, eliptical pore between eyes; opercular spine strong and slightly bent; cleithrum with sharppointed spine projecting posteriorly above pectoral peduncle; palatine teeth present; anterior gill arch with (2)–3 developed rakers; pelvic fins absent or with a single ray in each; pectoral fin lobe broader than long with 19–23 rays; precaudal vertebrae 15–16. The presence in males of a thick, fleshy, genital hood of which the copulatory organ is an integrated part and the joined vertical fins place Pseudonus in the subfamily Bythitinae .

Similarity. Pseudonus seems most similar to Bellottia Giglioli, 1883 by having short pectoral fin radials, presence of palatine teeth, lack of a prominent skin flap above opercle, and prominent head pores. Pseudonus differs by having a sharp spine on cleithrum above upper pectoral fin ray, lack of spines on lower angle of preopercle, presence of large interorbital pore, and a more slender body (body depth at origin of anal fin 10.5–13.5 % SL vs 13.0– 23.0 % SL). A DNA-based analysis has not been undertaken.

Species. Three species have been referred to Pseudonus ( Fig. 1 ):

P. acutus Garman, 1899 ,

P. platycephalus (Smith & Radcliffe, 1913) —described as Cataetyx platycephalus P. squamiceps ( Lloyd, 1907) – described as Diplacanthopoma squamiceps

Nielsen et al. (1999: 108) mention that P. squamiceps possibly is a senior synonym of P. platycephalus . In the description of Cataetyx platycephalus Smith & Radcliffe (1913: 169) noted that Diplacanthopoma squamiceps differs from their new species by the slightly longer head, fewer pectoral fin rays, a bifid pelvic fin, larger scales and origin of anal fin much nearer tip of caudal fin than tip of snout. It should be noted that Smith & Radcliffe (1913) did not compare their new species with the types of D. squamiceps but used the original description and the illustration in Lloyd (1908: pl. 42).

The comparison in Table 1 of the assumed separating characters of the two species is based on examination of two specimens from the squamiceps area (Gulf of Aden), characters from the original description of squamiceps and 12 specimens from the platycephalus area ( Philippines, Taiwan and Northwest Australia).

P. squamiceps (Gulf of Aden) P. platycephalus

2 syn-types BMNH USNM Philip+ Taiwan NW Australia

1939.5.24 227191 7 specimens 5 specimens Head length in % SL 28.5 28.5 26.0 24.5–27.0 24.0–25.5 Pectoral fin rays 19 20 19 19–22 21–23 Pelvic fin rays 1 1 1 1 1 Preanal length in % SL - 61 52 52–60 49.5–53 Scales in oblique row from anus - 20–25 20–25 25–30 25–30 Table 1 shows that none of the five separating characters mentioned by Smith & Radcliffe (1913: 169) remains after more specimens were included in the comparison between the two species. The two Gulf of Aden specimens (BMNH and USNM) show certain differences mainly in preanal length in % of SL (52 vs 61), but not more than found within P. platycephalus (52–60). Additional material from the northwestern Indian Ocean may confirm or invalidate the synonymizing of the two species.

It should be noted that the differences shown in Table 2 (interorbital length and distance from base of pelvic fins to anal fin origin) between the specimens from off Northwest Australia and those from the Philippines and Taiwan are so insignificant that the two populations must be considered conspecific.

The conclusion is that P. platycephalus is a junior synonym of P. squamiceps .

Figures

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