Distribution of Eudontomyzon sp. (Petromyzontiformes, Petromyzontidae) Ammocoetes and Diversity of Their Habitats in a Small Flat River of the Baltic Sea Basin

The resident nonparasitic lamprey Eudontomyzon sp., which differs from the only species of this genus known in the Baltic basin (Ukrainian lamprey E. mariae (Berg, 1931)), inhabits the Ilzhitsa River (drainage basin of the Western Dvina River). Eudontomyzon sp. larvae have been collected and the conditions of their habitat in the summer low water are identified. Abiotic and biotic characteristics of habitats are studied. The results of a morphological analysis of the river channel makes it possible to distinguish five types of biotopes: sediment in holes of the river bends (I), the sandy bottom on the straight regions of the river (II), the sediment in the pipes under the bridge (III), the sand and gravel spawning ground (IV), and the sediment at the river mouth (V). A study of the population density of lamprey larvae has made it possible to distinguish the most (I) and least (I, II, V) populated types of biotopes. An analysis of data on benthic communities has demonstrated that chironomids are the most typical representatives in the biotopes. This information complements the knowledge about the habitats of lamprey larvae with information about benthic communities in them and expand the existing classifications of habitats.