Contribution à l'étude du genre Pseudoscopelus (Chiasmodontidae) avec une espèce nouvelle, P. pierbartus n. sp., deux synonymies junior et une clé d'identification des espèces valides

The genus Pseudoscopelus Lutken, 1892 is easily distinguished from the other Chiasmodontidae by the presence of well-defined rows of photophores. Until 2005, eight species were known. Pseudoscopelus scriptus was the first described by Lutken in 1892, then P. sagamianus by Tanaka in 1908, P. stellatus by Beebe in 1932 and P. altipinnis by Parr in 1933. Later in 1934, Fowler described three new species: P. microps, P. cephalus, and P. obtusifrons. These three species, known from only one specimen each, have not been recorded since. Lastly, an easily distinguishable species, P. scutatus, was discovered by Krefft in 1971. In a recent review, Prokoviev and Kukuev (2005, 2006) confirmed the validity of all species and described a new one P. aphos, distinguishable by the absence of photophores. Our study proposes some different conclusion. A total of 58 specimens have been examined, four of them on photography. These fishes are deposited in the collections of the Museum d'histoire naturelle de La Rochelle (MHNLR), the Zoological Museum of the University of Copenhagen (ZMUC) or the National Museum of Natural History of Washingthon (USNM). We followed the standard method for counts and measurements. After examination, we describe a new species: P. pierbartus characterized by long pectoral fins extending beyond the 5(th) anal fin ray, teeth curved toward the front on the posterior part of the premaxilla and a photophore group on the caudal peduncle composed of three double rows forming an arrow in the direction of the head. We also propose to consider P. microps as a junior synonym of P. altipinnis and, similarly, P. cephalus with P. scriptus. P. scriptus, P. altipinnis and P. scutatus are three valid species and numerous specimens are available in museum collections. P. obtusifrons is also valid but few specimens seem to be available. The descriptions provided by Lutken, Parr, Krefft and Fowler allow their identification. According to Tanaka's original figure, the strong difference between P. sagamianus and P. scriptus is the position of the anus at a distance equal to the eye diameter of the anal fin. However, we didn't find a valid specimen. The types were lost and the 6 specimens from the examined materials identified as P. sagamianus were actually P. scriptus. Even Nakabo's illustrations of P. sagamianus (1993) show an anus close to the anal fin. So, to our knowledge, the validity of this species depends on the lost record of 1908. P. stellatus was not identified since its description by Beebe. The specimen is a juvenile and is too damaged for being re-examined. If the adult form is similar to that of the juvenile, this species will be valid. However, a study of juvenile forms of Pseudoscopelus is required. Finally, in the future, we recommend the group of photophores for identification and/or description of Pseudoscopelus spp.; a key is included to this study. Considering the numerous anatomical differences, like the presence of photophores and the form of the otoliths, between Pseudoscopelus and the other Chiasmodontidae, future study is required to determine whether the specimens currently included in the genus Pseudoscopehis should be placed in a new family.