L. Forró szerk.: Miscellanea Zoologica Hungarica 7. 1992 (Budapest, 1992)

Nesemann, H.: Species composition and zoogeography of the invertebrate fauna at the lower reaches of the Lajta River

T. transversalis (Figs 16-17) does not live in the Lajta any more. The species was exhumed from sandy sediments and became extinct before the end of the 19th century. Water pollution and river channelization seems to be responsible for the disappearance. Family Thiaridae Microcolpia acicularis (Férussac, 1823) Localities: Lajta near the confluence with the Mosoni-Duna 6. 9. 1991 (H); Zurndorf (Zurány) subrecent shells 23. 6.1991 (A); Gattendorf (Lajtakáta) subrecent shells 30. 6.1991 (A); Brack, subrecent shells in the deadwater reaches 16. 7.1991 (A); Rohrau, subfossil from sandy sediments (A). Living specimens were found near Mosonmagyaróvár (Fig. 18). The former distribution area included the lower and middle reaches of the Lajta. M. acicularis is a pontosarmatian prosobranche snail. This species is restricted to large rivers along the Pannonian reach of the Danube (Soós 1943, Pintér et al. 1979). It does not enter the upper Danube basin as far upstream as Vienna (Zilch & Jaeckel 1962). M. acicularis was able to reach the Bavarian Danube for several times during interglacial periods. Its uppermost distribution is recently bordered at the Vienna plain and lower reaches of the Lajta and Rába rivers. Esperiana esperi (Férussac, 1823) Locality: Mosoni-Duna near Dunaszeg 23.10.1990 (H). In contrast to M. acicularis, this species was not able to surmount the narrow valley of the Porta Hungarica (Falkner 1989). Its distribution range is bordered by the Kisalföld plain. Originally, E. esperi (Fig. 19) settled the lower reaches of the Lajta as far upstream as Nickelsdorf (Frank 1984). Here the species became extinct because of water pollution. Consequently, the uppermost record in the Danube basin is the Mosoni-Duna. E. esperi lives abundantly in the main stream of the Hungarian Danube. Family Bithyniidae Bithynia tentaculata (Linnaeus, 1758) Localities: Mosoni-Duna at Mosonmagyaróvár (Ungarisch Altenburg) 13. 9. 1991 (H); Lajta near the confluence with the Mosoni-Duna at Mosonmagyaróvár (Ungarisch Altenburg) 6. 9. 1991 (H); Rét-árok 30. 7. 1991 (A/H); Lajta-megyei-csatorna near Nickelsdorf (Miklóshalma) 9. 1991 (A/H); Rohrau 14. 5.1991 (A); Rohrau, in secondary branches 14. 5.1991 (A). B. tentaculata (Fig. 20) is widely distributed and very abundant in European lowland rivers. It is generalist in its habitat preferences and settles all types of running and stagnant waters (Zilch & Jaeckel 1962). Family Hydrobiidae Lithoglyphus naticoides (C. Pfeiffer, 1828) Localities: Mosoni-Duna near Mosonmagyaróvár (Ungarisch Altenburg) 13. 9. 1991 (H); Rohrau, subfossil shells from sandy sediments 1991 (A). This prosobranche snail (Fig. 23) is of pontocaspian origin and a typical member of the mud fauna of slowly running lowland rivers (Botos et al. 1990). In the Lajta, L. naticoides is no longer found in the middle reaches. The sub fossil record shows that, originally, this species settled as far upstream as Bruck (Clessin 1888, Frank 1984). The populations of the Lajta became extinct because of the channelization.