Bdelloid rotifers and nematodes in a small Italian stream

SUMMARY. The bdelloid rotifers and nematodes of a small clean watercourse in the area surrounding the Po river near Parma have been studied. The samples were collected at two sites 400 m apart. The species found in twelve collections of benthos between May 1977 and June 1978 were eighteen belonging to Bdelloidea and forty-seven to Nematoda (Tylenchida have not been considered). Nearly all the bdelloid species were oligosaprobic or beta-mesosaprobic; the Shannon index of diversity was 3.0 at the first site and 2.4 at the second. Among the Nematoda the dominant species were Paraplectonema pedunculatum and Paraphanolaimus anisitsi which were not previously recorded for Italy. Nearly all nematodes are microphagous; predators represent only 10% of collected specimens. Polluted water indicator species (Secernentia group) were only 3.5% of the total nematodes recorded. Most rotifers and nematodes did not show seasonal fluctuations in numbers. The two sampling sites do not seem to have substantial differences in the taxocoenosis of Rotifera and Nematoda; their percentage of similarity is 69% and 79% for the two classes respectively.