Characters of external morphology of Melanostomiidae fishes of genus Photonectes are critically analyzed. The features previously used to distinguish the subgenera are shown to be unfit for these purposes. Existence of only two decisively diagnosed subgenera is proven within the genus, Trachinostomias and Photonectes s. str., for which the revised diagnoses are given based on the new set of characters. Species P. uncinatus is moved from subgenus Trachinostomias to the nominative subgenus. Reasons for the separation of groups of species within the nominative subgenus and the phylogenetic relationships between these groups are briefly discussed. Three new species are described: P. distichodon, P. filipendulus, and P. xenopogon spp. n. Distinguishing features of another new species that is not yet described due to the lack of data are presented. The key for identification of all known species of the genus is presented.
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The greatly enlarged teeth near symphysis of the dentale were also noted in juveniles of P. dinema and P. phyllopogon; in these species, however, teeth of greatly differing size occur along the entire dentale (Fig. 1m). Teeth near symphysis in juveniles of other species (P. ex gr. albipennis, P. braueri, P. leucospilus, and P. paxtoni) do not differ from the subsequent teeth of dentale.
P. dinema, P. leucospilus, and P. paxtoni are known only from juvenile specimens.
In the sample ZMMU no. 14590, two of five specimens have four palatinum teeth on each side, and three other specimens have two, three, and five teeth, respectively. However, it cannot be excluded that the fishes from the western Indian Ocean are not conspecific with the Western Pacific fishes.
Described from the specimen SL 113 mm Photonectes sp. 2 (Parin et al., 1977), and is undoubtedly conspecific with P. paxtoni (Prokofiev, 2014); however, its description is too brief to estimate most of the characters of interest, and I was not able to track down the specimen. Nevertheless, based on the measurements given by Parin et al. (1977), the barbel length in this species should somewhat increase with growth, which excludes P. paxtoni being closely related to P. braueri, with which this species is most similar.
Both specimens are males according to dissection, but the holotype has completely immature gonads, whereas the paratype appears to be close to spawning.
Similar structure of the P ray was noted for some specimens of P. margarita (for example, ZMMU no. 23289), but it looks solid in other specimens of this species (attempts to separate it were unsuccessful).
The number of rows of praemaxillary teeth and the specifics of location of IP photophores are unknown for P. munificus, which nonetheless differs from the species of point 2(1) by a combination of homogenous (according to the figure of holotype in the first description) jaw dentition, BR 9, and rays of D and A, which are completely covered with skin. P. munificus is different from all other species of the genus by the features in the point 3(4) (except the number of rays in P).
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I am grateful to J. Maclaine (British Museum of Natural History), K. Webb (British Museum of Natural History), and J. Nielsen (Zoological Museum, University of Copenhagen) for providing photographs and data on syntypes of P. dinema and P. leucopogon.
The study of species composition of ichthyofauna of the mesopelagic zone was performed within the framework of state assignment no. 0149-2018-0009 and was supported by the Russian Science Foundation (project no. 19-14-00026); the study of morphology and systematics of Melanostomiidae fishes was supported within the framework of state assignment no. 0109-2018-0076. The writing of the present article was partially supported by the Russian Foundation for Basic Research, project no. 18-04-00019.
Conflict of interest. The authors declare that they have no conflict of interest.
Statement on the welfare of animals. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
Translated by A. Lisenkova
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Prokofiev, A.M. Materials for Revision of the Genus Photonectes (Melanostomiidae). J. Ichthyol. 59, 449–476 (2019). https://doi.org/10.1134/S003294521904012X
- external morphology
- subgeneric composition
- new species