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)

Wasser" (a dead-water reach) near Schönau (A), downstream Vienna, Oct. 1990; Rába at Győr (H), 28. Jul. 1990; Zala at Bókaháza (H), 31. May 1990 leg. FORRÓ & NESEMANN; Zala at Zalavár (H), 31. May 1990, leg. FORRÓ & NESEMANN; Lajta at Mosonmagyaróvár (H), 3. Mar. 1990; Leitha-Komitatskanal (Lajta bal parti csatorna) near Nickelsdorf (A), Sept. 1987; Leitha at Nickelsdorf (A), Sept. 1987, Oct. 1990; Leitha at Zurndorf (A), Sept. 1987; Leitha downstream Hollern (A), 26. Oct. 1990; empty shells of freshly dead animals also were collected from the Hungarian reaches of the Danube at km 1625 and 1560. This species originally has a Sarmatian distribution and is a typical member of the Danubian fauna. It also colonized some adjacent drainage areas (Po, Axios) during the Pleistocene, where it still lives as a relict. T. danubialis is the most common Neritidae of the Carpathian Basin. Recently it has settled in the Danube upstream to Bavaria near Kehlheim (LEUCHS & TITTIZER 1989). It seems to have a partially disjunct range, because it prefers mostly lowland rivers with a moderate velocity of flow. It was found in large numbers in the Danube only in the Hungarian reaches. Its recent occurrence in the Austrian Danube is restricted to abandoned river lakes with a fauna very rich in Ponto-Caspian species. Elsewhere T. danubialis colonizes the lower reaches of other rivers (Lajta, Rába, Zala) at high densities of individuals. Theodoxus fluviatilis (Linnaeus, 1758) (Figs 6-7) Localities: Danube at Érd-Ófalu (H), km 1625.4, 30. Jan. 199L leg. WIMMER & NESEMANN, for further records (Tisza) see PINTER, RICHNOVSZKY & SZIGETHY (1979). T. fluviatilis is a new prosobranchiate snail to the Hungarian Danube. It is widely spread all over Europe including Anatolia, but does not belong to the original Danubian fauna. Its occurrence in the Carpathian Basin was first recognized for the river Tisza (HORVÁTH 1943), wherein T. fluviatilis allopatrically takes the place of T. danubialis. In general the working hypothesis is accepted, that T. fluviatilis is a Pleistocene immigrant. The species could possibly enter the upper Tisza by river capture, arriving from the Baltic drainage area. The species is a characteristic member of the rheophile fauna of large rivers and littoral zones of lakes. In the southern parts of the settled area, T. fluviatilis is also known from springs and brooks occasionally. Its geographical distribution pattern in the Rhine Basin is very similar to that of the leech Erpobdella nigricollis and the freshwater bivalve Unio tumidus Philipsson, 1788. It prefers overflowed gravelly and stony bottoms. Fam. Thiaridae Fagotia acicularis (A Ferussac, 1823) (Fig. 15) Localities: Danube at Dunaföldvár (H), km 1560.8, 31. Jan. 1991, leg. WIMMER & NESEMANN; Danube at Érd-Ofalu (H), km 1625.4, 30. Jan. 1990, leg. WIMMER & NESEMANN; Szentendre Duna between Tahitótfalu and Leányfalu (H), 31. May 1989, leg. PUKY & NESEMANN; Danube at Visegrád (H), km 1693.6, 31. May 1989, leg. PUKY & NESEMANN; Danube near Hainburg (A), in a secondary branch "Unterer Tiergartenarm", Apr. 1989; Danube near Schönau (A), in a dead-water reach "Kühwörther Wasser", Oct. 1990; Rába at Győr (H), 28. Jul. 1990. The members of the Thiaridae family originally belong to the Pontosarmati-