Calicotyle confusa n. sp. (Monogenea: Monocotylidae) from Okamejei boesemani (Elasmobranchii) off Vietnam.

Monogeneans of the genus Calicotyle Diesing, 1850 were found in the cloaca of the Arafura skate Okamejei boesemani (Ishihara, 1987) from the coastal waters of Vietnam. A partial 28S rDNA sequence (822 bp) was obtained from the collected specimen and deposited in GenBank (accession number PP868284). Comparative analysis with the available 28S rDNA sequences of Calicotyle spp. in the NCBI database revealed the smallest p-distances with the C. kroyeri Diesing, 1850 species complex. However, the genetic distance between the obtained sequence and C. kroyeri (AF279746) from its type host, Amblyraja radiata (Donovan, 1808), and type locality (the North Sea), was 4.2 %, while distances from all C. kroyeri isolates from the Atlantic Ocean (AF279744 - AF279747) ranged from 4.2 to 5.9 %. Based on these results, a new species, C. confusa n. sp., was proposed. Morphologically, C. confusa n. sp. exhibits smaller, albeit overlapping, dimensions compared to C. kroyeri specimens from the North Atlantic. However, no significant differences were observed between the two species in taxonomically important characters. Further morphological studies of C. kroyeri from its type host, as well as from other hosts and regions, are required to identify potential diagnostic characters distinguishing it from C. confusa n. sp.