Host Range and Phylogenetic Position of Acipenserobdella volgensis (Zykoff, 1904) (Hirudinea: Piscicolidae) with a Global Checklist of Bivalve-Associated Fish Leeches

The fish leech Acipenserobdella volgensis (Hirudinea: Piscicolidae) is a rare and poorly known freshwater species, which is thought to be an obligate parasite of sturgeons. This leech has a disjunctive range in Europe and eastern Siberia. Here, we estimate the phylogenetic affinities and host range of A. volgensis using a set of DNA sequences (COI and 18S rRNA gene fragments), field observation data, and a review of the body of literature. Based on a time-calibrated Bayesian phylogeny, we show that the European and Siberian lineages of A. volgensis have been separated since the latest Pliocene (mean age = 2.7 Ma). The analysis of available host records indicates that this leech is characterized by a broader host range as it was collected from fish belonging to four families (Acipenseridae, Cyprinidae, Salmonidae, and Esocidae). Conversely, only a few suitable primary hosts (six sturgeons, one cyprinid, and one salmonid fish) were confirmed by earlier research. Moreover, this leech could be considered a facultative mussel-associated species that uses bivalves (duck mussel Anodonta anatina; Unionidae) as shelter. Globally, three other piscicolid leeches have been recorded from the mantle cavity of bivalve molluscs, that is, the freshwater taxa Caspiobdella fadejewi and Alexandrobdella makhrovi, and the marine species Austrobdella coliumicus.