The identity and occurrence of Kerona pediculus (Ciliophora: Hypotrichida), a well-known epizoite of Hydra vulgaris (Cnidaria: Hydrozoa)

Epizoic Kerona pediculus have been found on Hydra vulgaris and on Cristatella mucedo (Bryozoa) in the same habitat. On the basis of morphological characters (using Nomarski and Scanning Electron Microscopy) specimens from the two hosts are indistinguishable. Details revealed by SEM agree with previous results from silver staining, confirming the identity of K. pediculus. The taxonomic status of this species is briefly summarised. Host recognition, the inhibition of nematocyst discharge, and the possible role of host growth-promoting substances are not yet understood.