Resolving phylogenetic relationships and taxonomic revision in the Pseudogastromyzon (Cypriniformes, Gastromyzonidae) genus: molecular and morphological evidence for a new genus, Labigastromyzon.

Abstract

The Pseudogastromyzon genus, consisting of species predominantly distributed throughout southeastern China, has garnered increasing market attention in recent years due to its ornamental appeal. However, the overlapping diagnostic attributes render the commonly accepted criteria for interspecific identification unreliable, leaving the phylogenetic relationships among Pseudogastromyzon species unexplored. In the present study, we undertake molecular phylogenetic and morphological examinations of the Pseudogastromyzon genus. Our phylogenetic analysis of mitochondrial genes distinctly segregated Pseudogastromyzon species into two clades: the Pseudogastromyzon clade and the Labigastromyzon clade. A subsequent morphological assessment revealed that the primary dermal ridge (specifically, the second ridge) within the labial adhesive apparatus serves as an effective and precise interspecific diagnostic characteristic. Moreover, the distributional ranges of Pseudogastromyzon and Labigastromyzon are markedly distinct, exhibiting only a narrow area of overlap. Considering the morphological heterogeneity of the labial adhesive apparatus and the substantial division within the molecular phylogeny, we advocate for the elevation of the Labigastromyzon subgenus to the status of a separate genus. Consequently, we have ascertained the validity of the Pseudogastromyzon and Labigastromyzon species, yielding a total of six valid species. To facilitate future research, we present comprehensive descriptions of the redefined species and introduce novel identification keys.