THE HABITATS OF LYMNAEA-TRUNCATULA MULLER (MOLLUSCA) ALONG 2 RIVER BANKS

Malacological investigations were carried out over 1994 and 1995 along two river sections to count and to determine the characteristics of t he habitats of the snail Lymnaea truncatula. The two river sections st udied were a) along a 10 km stretch of the River Creuse near Argenton- sur-Creuse (Indre) and b) along 25 km section of the River Vienne from Saint-Victumien (Haute-Vienne) to Etagnac (Charente). A total of 27 s ites inhabited by L. truncatula were found along the Creuse river. Gre at fluctuations in snail abundance were noted : 6 habitats had less th an 10 L. truncatula in July, 9 had 11 to 20 snails, 6 had 21 to 50 sna ils, and the remaining 6 had more than 51 snails. The length of these habitats did not exceed 5 m in 15 cases, 10 m in 6 cases, 15 m in 4 ca ses, and 35 m in the 2 other stations. A total of 9 sites containing L . truncatula were noted along the 25 Irm of the Vienne river. More tha n 101 snails were recorded at one station in June while less than 50 w ere obtained in the 9 other sites. The habitat length was less than 5 m of river bank in 8 sites and 35 m in one site. it is concluded that these river banks did not constitute favourable sites for the developm ent of L. truncatula populations.