LAUSR

During a re-examination of macrozoobenthic samples from a long-term monitoring programme in the Dutch Oosterschelde and Westerschelde, the abundant presence of peritrich ciliates on specimens of Bathyporeia Lindstrom, 1855, was discovered. Out of the more than 3500 Bathyporeia specimens investigated, 44% contained ciliates. Although Bathyporeia sarsi Watkin, 1938 was significantly more often infested than Bathyporeia pilosa Lindstrom, 1855, these differences in infestation rates were largely due to differences between water bodies with higher infestation rates in the polyhaline than in the mesohaline reach. Observation of additionally collected living specimens and freshly preserved material showed that at least two, and likely three, species of ciliates are present of which two might be undescribed so far. One of the observed species matches Zoothamnium nanum Kahl, 1933. A second species belongs to the genus Epistylis Ehrenberg, 1830, but does not seem to match a so far known species. This also accounts for a possible third species belonging to the genus Zoothamnium Bory de St. Vincent, 1826, deviating from Z. nanum amongst others in the habitus of the stalk. The front part of Bathyporeia spp. and the antennae in particular, significantly more often harboured ciliates than the remainder of the body, where additional ciliates were only found on the ventral side. This shows that the peritrich ciliates benefit from the water currents induced by the basibiont, providing food items, but might also indicate that Bathyporeia spp. benefits from the presence of the epibionts as they are most prevalent on the body parts that are easiest to clean. Analyses of densities and distributions of epibiont and basibiont species gave first indications of the ecological niche of the peritrich ciliate communities.