L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)

Nesemann, H., Pöckl, M.; Wittmann, K. J.: Distribution of epigean Malacostraca in the middle and upper Danube (Hungary, Austria, Germany)

Fig. 3a-b. Dikero gammarus villosus, different colour variants from dorsal and lateral view, from Danube at Dunaremete so-called "Ecosystem Study Altenwörth" (Pöckl 1988). For the first time (1989) in Austria, D. villosus was collected by the present authors at several sites, where it was quite abundant. In September 1992, D. villosus was found for the first time abundantly in the Bavarian Danube near Straubing and Regensburg. Recently, D. villosus invaded successfully the River Rhine, where it was sampled in the Netherlands (Bij de Vaate & Klink 1995) and in southwestern parts of Germany (leg. M. Spangenberg). Because of their extreme body dimensions, it seems rather unlikely that specimens of D. villosus were overlooked in the past. Adult males reach up to 30 mm total body length. The colouration of living animals is highly variable (Figs 1-3) but spectacular, most frequently showing a light spot or stripe per segment on a dark background. Pale specimens can also be found but it is suggested that they have moulted most recently. In the preserved material the natural colouration disappears within a few days. D. villosus is found in rockpools and under porous stones, creeping most deeply into the holes where it seems to be rooted, so that it is pulled out only by force. During periods of low water level the rockpools, inhabited by gammarids, may fall dry. Obviously, the abundance of the animals seems to be significantly dependent on water discharge.