A new leech species (Clitellata: Hirudinida: Piscicolidae) from the Łyna River near Olsztyn, Poland.

A new species of fish leech from Poland, Piscicola burresoni n. sp. (Piscicolidae), is described. The leech was found in 2007 on stones and on pike ( Esox lucius L.) and chub ( Leuciscus cephalus L.) in the Łyna River, Poland. The leech is small, relatively flattened, with a prominent coarctation between the trachelosome and urosome. The pigmentation is unique to the new species and it has 14 annuli with gonopores separated by 4 annuli. The receptaculum seminis consists of an elliptical aperture located at a distance of 3 annuli behind the female gonopore. The copulatory area on the clitellum is characteristic in the shape of a parallel ellipse. The vector tissue is in the form of a transverse plate below the oviduct outlet. For a complete description of the external morphology, a geometric-mathematical model of the leech body form was used.