Overview of Antarctic icefish species of the genus <em>Channichthys</em> Richardson, 1844 (Notothenioidei: Channichthyidae) based on morphological studies

The study presents the results of a most recent comprehensive review of the morphology of little-studied endemic Antarctic icefishes of the genus Channichthys Richardson, 1844 (family Channichthyidae). It aims at a detailed taxonomic revision in order to analyze their general similarity and relationships and to conclude on the exact species composition of this genus. Previously, there was reported from 1 polymorphic to 9 separate sympatrically widespread species within the genus Channichthys, while the validity of most species remained questionable up to date. In this study, the structure of the gill apparatus and the seismosensory system have been studied along with the up-to-date methods of digital microfocus radiography and statistical methods accompanied by conventional methods of analyzing the external morphology of fish. The representatives of all nine species listed previously in different publications were analyzed with strict reference to museum collections. As a result, the validity of only four out of nine nominal species of the genus Channichthys was confirmed: Ch. rhinoceratus, Ch. rugosus, Ch. velifer, and Ch. panticapae. The validity of five other species has not been confirmed: three species (Ch. aelitae, Ch. mithridatis, and Ch. richardsoni) are conspecific with Ch. rhinoceratus, while two species (Ch. bospori and Ch. irinae) with Ch. panticapae. Most of their distinctive morphological characters, identified previously as indicators of the species level, overlap with those of valid species. Improved differential diagnoses of valid species of the genus Channichthys have been compiled, including key features that make it possible to identify the species of this genus correctly.