Sedentary ciliates from two Dutch freshwater Gammarus species

The sedentary ciliate fauna living on the body surface of Gammarus tigrinus and G. pulex from Dutch freshwater habitats has been investigated. Fourty-seven ciliate species are found, of which 43 belong to the order Peritrichida, suborder Sessilina, 3 belong to the order Suctorida and 1 belongs to the order Chonotrichida. Two new species in the genera Intranstylum and Pseudocarchesium are described. It appears that there is a seasonal variation in the number of epizoic ciliates as well as in species composition. In general, the species with a contractile stalk are found on external, often fast-moving, body parts. Species with a noncontractile stalk seem to prefer more quiet and sheltered positions. After ecdysis there is a succession of the genera Epistylis and Zoothamnium, the latter becoming dominant on older exoskeletons.