Pseudoscopelus Luetken

[[Pseudoscopelus Lütken]]

Four genera are currently recognized in Chiasmodontidae, one of the few families of bathy- and mesopelagic fishes in the large actinopterygian order Perciformes (Nelson, 2006): Chiasmodon Johnson (1864); Pseudoscopelus Lütken (1892); Dysalotus MacGilchrist (1905); and Kali Lloyd (1909). Pseudoscopelus is the most species rich genus with 15 nominal species, 12 of which are valid (Table 1). Most of these species have light organs, which are restricted to Pseudoscopelus within the family. The genus has a worldwide distribution, being found in all major ocean basins, even off Antarctica, but is absent from the Mediterranean and Red Seas. In the present study, two new species of Pseudoscopelus are described, P. lavenbergi from the eastern Pacific, and P. bothrorrhinos from the western Pacific and Indian Oceans.

The genus Pseudoscopelus was initially diagnosed by Lütken (1892) based on the presence of lines of mucous pores [sic] along the body. This definition had been followed by subsequent authors (e.g., Tanaka, 1908; Norman, 1929), until Beebe’s (1932) discovery that instead of mucous pits, the lines over the body of Pseudoscopelus were actually formed by photophores that produce a clear, bright light. Since Beebe’s work, the genus has been defined by the presence of discrete photophores along the body (e.g., Mooi and Paxton, 2001; Nelson, 2006). In 1974, Lavenberg revised the genus Pseudoscopelus for his PhD; he considered six species to be valid and listed six other new taxa, but never published his results according to the ICZN (1999) rules. The most recent works have been published by Prokofiev and Kukuev (2005, 2006a, b, c) who described four new species; two of which, P. aphos and P. parini, totally lack discrete photophores. Prokofiev and Kukuev (2006c), however, still regarded the presence of photophores as a generic character.

Pseudoscopelus is diagnosed herein by two synapomorphies, present in all species. Using this as the diagnosis would also include Myersiscus Fowler (1934), which was erected during the description of P. obtusifrons and was then considered a junior synonym of Pseudoscopelus exclusively because of the presence of photophores (Mooi and Paxton, 2001; Prokofiev and Kukuev, 2005, 2006c).