Distribution of Pseudamnicola confusa in the Deltaic region of Rhine and Meuse The small snail Pseudamnicola confusa has been found in 14 localities in the Deltaic region of the rivers Rhine and Meuse, inhabiting fresh as well as oligohaline waters under estuarine conditions. It is an intertidal species, which is very sensitive to currents. Therefore it lives mostly in the upper part of the eulittoral belt, where it is sheltered against the currents by the vegetation. In the fresh water area it occurs most commonly in the willow coppices along the edges of small tidal creeklets and depressions, characterized by a vegetation of Callitriche stagnalis and Polygonum hydropiper. Another biotope are the extreme ends of long mezzanine-ports. In the oligohaline area it has been mainly found in depressions of the outer marshes, which are flooded at high tide. It has been discovered also in the middle part of the intertidal belt, under large boulders. Thus the potential vertical range is much wider than the actual vertical range in the other biotopes. The species tolerates a rather strong pollution; nevertheless it could be found only in the marginal part of the Rhine-sector with its anthropogenously increased saltcontent, although suitable biotopes are available in the whole sector.