Distribution of Schellencandona rhodanensis sp. n. A. Vertical distribution in the sediment of the Valbonne gravel pit from March 1980 to September 1983 (mean abundance and standard error; n=6 sampling dates per depth). B. Lateral distribution in the wetlands of the Ain River (Puits Novet and Brotteaux) located close to the confluence with the Rhône River, at 16 sites, at −50 cm and −100 cm deep inside sediments, from March 1985 to September 1986 (n = 6–9 samples). Black square: species present in at least one sample. White circle: species absent. C. Altitudinal distribution in the bed sediment of the Albarine River, at 12 sites ranging from 939 to 220 m a.s.l. The size of the circle is proportional to the abundances (number of individuals per 10 L of pumped water).