The radiation of Thaparocleidus (Monogenoidea: Dactylogyridae: Ancylodiscoidinae): phylogenetic analyses and taxonomic implications inferred from ribosomal DNA sequences.

The monophyly of Thaparocleidus Jain 1952 and its phylogenetic relationship with Pseudancylodiscoides were assessed using the D1-D2 domains of the large-subunit ribosomal deoxyribonucleic acid sequences, and taxonomic implications were discussed concerning the relative taxonomic importance of the characters of the reproductive complex and those of the haptoral scleties for future genus erection and combination within the Ancylodiscoidinae. Thaparocleidus contained divergent genetic lineages and was not resolved as a monophyletic group. The first lineage was represented by two species found on Pangasium sutchi (Pangasidae), and the second one contained 12 species all from Silurus astus (Siluridae). Three clades were observed for species from S. astus, consistent with results of morphological analyses, indicating that 12 Thaparocleidus species could be divided into three groups by morphological examinations of the male copulatory organ (MCO). Pseudancylodiscoides spp. was more closely related to Thaparocleidus spp. from S. astus, and morphologically, it was found that shapes of MCOs of these species were the same type but different from that of Thaparocleidus spp. from P. sutchi. Therefore, based on results of molecular phylogenetic analyses and morphological examinations, we propose to abolish Pseudancylodiscoides and to erect a new genus to accommodate Thaparocleidus species from S. astus and Pseudancylodiscoides spp. It is also suggested to erect another new genus to accommodate two Thaparocleidus species from the P. sutchi, whose MCO shapes are different from other Thaparocleidus species.