Pseudoscopelus Luetken

Marcelo R. S. Melo, H. J. Walker, Jr. & Cynthia Klepadlo, 2007, Two new species of Pseudoscopelus (Teleostei: Chiasmodontidae), with a new diagnosis for the genus., Zootaxa 1605, pp. 33-46 : 44-45

[[ Pseudoscopelus Luetken ]]

Discussion

Within the family Chiasmodontidae, Pseudoscopelus is the only genus with photophores, but two described species, P. aphos and P. parini , lack this characteristic. Prokofiev and Kukuev (2006c) provided other generic characteristics to define the genus, “characteristics of jaw dentition, (...) peculiarly striated and cancellated cranial roofing bones.” Teeth of Pseudoscopelus are of type 1 or 4, arranged in three series in the premaxilla, and two in the dentary (as described herein for P. lavenbergi and P. bothrorrhinos ), a pattern that is similar to Dysalotus with specific variations. Similar to Pseudoscopelus , bones that form the roof of the cranium in Chiasmodon (i.e., supraoccipital, parietals, and frontals) are also grooved, with crests in the frontals.

The validity of Pseudoscopelus is supported by two synapomorphies present in all species: the dorsal margin of the orbit is formed by infraorbital 6; the position of the last infraorbital pore in the dorsal edge of the orbit is anterior to the middle of the pupil (see Fig. 2). It is further differentiated from Kali and Dysalotus by having a well calcified spoon-shaped nasal, in the lateral or anterior sides of the snout, covered by thin transparent skin (vs. nasal weakly calcified, circular but not spoon-shaped, positioned in the dorsal part of the snout, and covered by pigmented skin), and by having the last scale of the lateral line well separated from the penultimate scale and positioned over the lower lobe of the caudal fin (vs. last lateral-line scale contiguous with penultimate scale), and by the presence of pre- and postzygapophyses (vs. absent in Kali and Dysalotus ). From Chiasmodon , it also differs by the absence of a well developed fang in the anterior edge of premaxilla (vs. fang present in Chiasmodon ), and by a reduced number of pores associated with infraorbital 1 (4-5 vs. 8- 9 in Chiasmodon ). As defined herein, Myersiscus is regarded a junior synonym of Pseudoscopelus .

Pseudoscopelus altipinnis was described by Parr (1933) based on two specimens collected off Cat Island, Bahamas. One year later, Fowler (1934) described P. microps based on a single specimen collected in the Gulf of Boni, off Sulawesi Island, Indonesia, apparently not knowing about Parr’s work, nor describing P. microps adequately. Prokofiev and Kukuev (2005, 2006a) recognized eight species of Pseudoscopelus , including P. altipinnis and P. microps , as valid, even though they did not compare the type specimens of any species. Later, Prokofiev and Kukuev (2006c) followed Lavenberg (1974) in recognizing P. altipinnis as the senior synonym of P. microps , and altered the diagnosis of P. altipinnis provided in their first work, although again they did not examine type specimens. A comparison of primary types by the senior author (MM) confirmed the status of P. altipinnis as the senior synonym of P. microps , in agreement with Lavenberg (1974).

Prokofiev and Kukuev (2006c) also followed Lavenberg (1974) in recognizing P. stellatus Beebe (1932). Pseudoscopelus stellatus was described based on five larval specimens between 6.5 mm and 20.3 mm, obtained off Bermuda. Beebe (1932:75) listed the lot NYZS 21155 as the type (now USNM 170941), and mentioned three other lots during the species description, considered as paratypes by Eschmeyer (2006): NYZS 21321, 1 (now CAS-SU 66494), 21404, 2 (now CAS-SU 66497), and 21456, 1 (CAS-SU 66496). The lot USNM 170941 clearly has photophores along the body, as described and illustrated by Beebe (1932:76), but the other lots lack photophores. A study of the ontogenetic changes in the photophore pattern of Pseudoscopelus is ongoing; meanwhile, the status of P. stellatus should be regarded as species inquerida.