We examined the settlement preferences of leeches by analysing colonization patterns on artificial substrates. The intention was to check whether the type of material, texture and size of artificial substrates would influence the abundance of leeches. To test substrate type preferences, we used the following nine artificial substrates: polyester, polycarbonate, aluminium, glass, rubber, steel, polyethylene, ceramics and polypropylene. In addition, substrates of different textures (structural vs. smooth) and sizes (900, 400, 100 cm 2 ) were used. We found that rubber, polyethylene and aluminium were most frequently chosen by the leeches. Surface structure and size of the objects were other factors which determined substrate selection by these organisms. Leeches more readily inhabited rough surfaces and the surfaces of smaller-sized objects. The species composition of leech assemblages on analysed artificial substrates was dominated by predatory taxa of the genus Erpobdella and Helobdella.

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I n t e r n a t i o n a l J o u r n a l o f O c e a n o g r a p h y a n d H y d r o b i o l o g y AbstractHirudinida comprise a constant component of benthofauna in running waters and their taxonomic composition is often analyzed to evaluate the environmental quality. However, the indicatory role of particular species is still arguable. Thus, it is very important to provide more detailed information on the impact of environmental parameters on the species structure within this group of invertebrates. Representatives of nine species were found in the investigated upland stream including mainly Erpobdella vilnensis and E. octoculata. The research has demonstrated that the hydromorphological conditions and feeding behavior are the main factors determining the taxonomic composition of leeches in particular sections of a watercourse.

Chironomus melanotus Keyl, a new species of Polish fauna, is described on the basis of cytogenetic characteristics. It belongs to the cytocomplex thummi with the chromosome set 2n = 8, chromosome arm combinations AB CD EF G and species-specific karyotype markers.Two types (somatic and inherited) of structural chromosome rearrangements in salivary gland chromosomes were identified in the species and somatic rearrangements (heterozygous inversions, deficiencies, deletions — Somatic index — 0.54) were observed for the first time in this species. In addition to those in the mosaic state, some genome alterations — trisomy and “B” chromosome, as well as larval malformations (10.27%) were detected for a first time. The malformations and somatic structural and genome aberrations may have been caused by different stress agents in the environment. Thus, we suggest that the high spectrum of somatic rearrangements observed in C. melanotus may indicate the existence of pollution (elevated Cd and Pb concentrations) in Lake Łuknajno (the study area) and perhaps trace metals and different chemicals produced by the Chara species.

The largest rivers in Europe are under strong human pressure, resulting in habitat changes and consequently in structural changes in the quantitative and qualitative composition of fauna assemblages. The aim of this study was to identify the taxonomic structure of leech assemblages and the main environmental factors influencing their distribution pattern on a 306 km stretch of the Oder River encompassing different habitat types. Representatives of 28 leech taxa were recorded in 527 samples of bottom macrofauna. The most abundant and most frequently recorded species was the eurytopic