Emys orbicularis is receding from Europe, mainly due to anthropogenic habitat changes. Its parasite, Placobdella costata, is widely distributed within both the former and the present distribution range of the host. Though closely associated with the mud turtle, it may have other hosts (birds, amphibians, reptiles). Its reproductive period coincides with that of its host's migration to the breeding grounds, thus facilitating dispersal of the parasite. Based on literature data we have analyzed the geographic spread of P. costata and mud turtle to observe the possible overlap of their habitats. Observations on the population of mud turtle and the associated leech species (P. costata) were carried out in eastern Poland -Podlasie Lowland. The studies were conducted in spring and summer in 1986-1993. The leeches were collected from the turtles caught in the water and on land. Observations showed that most leeches were found on turtles inhabiting the lake or moving to a breeding area. The greatest intensity of invasion was observed in June and July and that most leeches were observed in female E. orbicularis characterized by greater length of the carapace and weight, compared with males and juvenile individuals.

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.

For the first time, Piscicola brylinskae was described from Lake Vechten in the village of Bunnik, near Utrecht -The Netherlands. Until now, P. brylinskae has been found in Poland in Lake Maróz and in the Lyna River near Olsztyn (the northern part of Warmian-Masurian voivodeship). Thanks to proper conservation the coloration of P. brylinskae was described for the first time. Applying 32 indexes resulted that P. brylinskae clustered to Caspiobdella fadejewi. Analysis based on 113 non-metric characteristics has shown that P. brylinskae is most similar to Piscicola margaritae. Though, P. brylinskae do not form with P. margaritae dichotomic branching nor with any other species from this cluster, it could confirm that it is an individual species of the Piscicola genus.

Batracobdelloides moogi, the species representing the afroasiatic genus, is very poorly known for its biology and anatomy. This species was described on the basis of a small group of samples from south-western Europe. This study presents a morphological analysis and description of the structure of the alimentary tract and reproductive system. Biometry and external morphology were analyzed on 96 individuals and the anatomic structure on 40 individuals. The average length of the examinated specimens was 9.81 mm and the average weight was 0.056 g. The length of proboscis ranged from 2.5 to 4 neurosomites. Lengths of each ovary ranged from 1.5 to 3.5 neurosomites. Lengths of left and right sperm ducts ranged from 0.5 to 2.5 neurosomites. Correlation between the length of sperm ducts and their coiling was recorded.