New data about the functional morphology of the chaetiferous leech-like annelids Acanthobdella peledina (Grube, 1851) and Paracanthobdella livanowi (Epshtein, 1966) (Clitellata, Acanthobdellida).

Approximately 130 individuals of Acanthobdella peledina and 100 individuals of Paracanthobdella livanowi were studied. Morphometric measurements were taken to explore the body form. The digestive and the reproductive systems of leech-like annelids were analyzed for the first time in such a high number of specimens. Observation of A. peledina and P. livanowi revealed crucial differences in the reproductive system of the analyzed taxa, mostly regarding variation in the shape of the testisacs and the length of the ovisacs. The results of a digestive system analysis suggest that blood-sucking parasites of the order Acanthobdellida may also lead a predatory lifestyle. The presented findings support the taxonomic division of the order Acanthobdellida into the families Acanthobdellidae and Paracanthobdellidae. Multiple similarities between Acanthobdellida and Hirudinida were also discussed.