L. Forró - É. Murai szerk.: Miscellanea Zoologica Hungarica 6. 1991 (Budapest, 1991)

Nesemann, H.: Zoogeography and composition of leech fauna of Danubian lowland rivers in the Kisalföld compared with some molluscs (Hirudinea, Gastropoda)

MISCELLANEA ZOOLOGICA HUNGARICA Tomus 6. 1991. p. 35-51 Zoogeography and composition of leech fauna of Danubian lowland rivers in the Kisalföld compared with some molluscs (Hirudinea, Gastropoda) by II. NESEMANN (Received March 25,1991) Abstract: 24 species of Hirudinea were found in the alluvial floodplains of 7 rivers of the Kisalföld between 1987 and 1991. Ten of them are typical members of the Potamon biocoenosis and are restricted to the lowlands in the basin of the River Danube. The main distribution patterns are compared with those of some prosobranchiate snails (Thiaridae, Neritidae) and zoogeography is also concerned. A few Pontocaspian or Pontomediterranean species had not been recorded anywhere in Central Europe earlier. Keywords: Hirudinea, Gastropoda, distribution, lowland rivers INTRODUCTION Even today, the freshwater fauna of the River Danube is relatively unknown. The Pontocaspian rivers are the most important and oldest running waters in Europe. A permanent development of the European freshwater fauna has been taking place since Miocene drying up and dulcifying the former marine Paratethys Sea. The Preglacial Eumediterranean or Paleoeuropean fauna was formed using the former Egean river systems and the Pontosarmatian basins as a symmetry axis for spreading. Due to climatic changes during Pleistocene glaciation, the "oldest" groups (Thiaridae, Corbiculidae) have lost the northern part of their distribution and the fauna was influenced strongly by the more recent Eurosiberian fauna. The Danube became an important pathway to the northwest serving the invasion of formerly lost areas. The most important characteristics of the recent faunal composition in the Central Pontocaspian and Sarmatian Basin were separation and relict character during the upper Pliocene and Pleistocene (BOTHÁR 1966, KROLOPP 1978, BALON 1968). While other parts of Europe were completely influenced by glaciation, here several species of the former fauna survived. At the same time the freshwater fauna of the listed basins developed further strongly. In the light of geographical and faunal history the origin of the recent Danubian freshwater fauna is understandable. It comprises several groups with different distributional patterns: (a) Eurosiberian species with a wide distribution, (b) Pontocaspian and Pontosarmatian "endemic" species in the separated drainage area, e.g. Limnomysis benedeni (WEISH & TÜRKAY 1978) and (c) Pontomediterranean species. The faunal members of (b) and (c), which originated from the Paleoeuropean fauna (KINZELBACH 1987), have much more specifications and fossil connections to the Tertiary fauna. Therefore the Danube contains more freshwater species than other river basins. In this paper the first results of the study on faunal composition and species richness are presented for the freshwater leeches. Most of the species are similar regarding the main pattern of distribution. The biological classification of the investigated rivers is discussed. Zoogeographical barriers and pathways are also shown.