How many species are in the genus Mesanophrys (Protista, Ciliophora, facultative parasites of marine crustaceans)?

Summary The paper presents the morphometric characteristics of the histophagous ciliate Mesanophrys found in the hemolymph of the isopod Saduria entomon from the Baltic Sea. The ciliate is compared with another, very similar one, found free-living on the coast of Vancouver Island, British Columbia, as well as with all literature data on the genus Mesanophrys . The ranges of all morphometric characters among these ciliates and all Mesanophrys species described so far strongly overlap. It seems, therefore, that the available morphological data, in the absence of other criteria, do not justify distinguishing separate species. The two ciliates presented here, as well as all nominal Mesanophrys species, should be referred to M. maggii (Cattaneo, 1888) unless new evidence concerning host specificity, life cycle or biochemical dissimilarity, for example, indicates a taxonomic difference.