Genetic Variability of Two Evolutionary Distinct Classes of the Acanthocephala Isolated from European Chub from Rivers of the Adriatic and Black Sea Basins in Croatia

Abstract The aim of our study was to investigate the genetic variability of two members of two evolutionary different classes of the Acanthocephala, Eoacanthocephala ( Neoechinirhynchus sp.) and Palaeacanthocephala ( Acanthocephalus sp.) from the same host, Squalius cephalus , from rivers of the Adriatic (rivers in Lika region: Lika, Novčica, Bogdanica and Jadova) and the Black Sea basins (Medsave location on the Sava River) in Croatia. The samples were collected from May 2021 to July 2022. To put the genetic position of the analyzed acanthocephalans in a broader context, the COI sequences of other specimens from the NCBI GenBank were used. BLAST analysis of partial COI sequences of acanthocephalans showed the presence of two different species: Acanthocephalus sp. and Neoechinorhynchus sp. Acanthocephalus sp. specimens did not show different grouping related to geographical origin (Bogdanica, Lika, Jadova) or Black Sea basin (Medsave-Sava River). Acanthocephalus cluster was subdivided into five main subclusters and 13 haplotypes were determined. When we compared our haplotypes with those from the NCBI GenBank, our haplotypes were closer to the A. anguillae specimens from the Kupa River and Dobra River in Croatia, and also to the haplotypes from Austria. For the species Neoechinorhynchus sp. from the Lika River and the specimens from the NCBI GenBank, four haplotypes were found out of five specimens. This genus was recorded for the first time in the Lika River area and for the first time in European chub in Croatia. The closest species Neoechinorhynchus sp. from Austria and Finland were grouped separately. Due to the lack of NCBI GenBank data for this species from other geographical regions, our data could not be compared. This shows that the taxonomy of the genus Neoechinorhynchus from Europe remains a challenge and underlines the need for further DNA sequence data and in-depth morphological study.