Tetrahymena chironomisp.nov., a ciliate from midge larvae, and the current status of facultative parasitism in the genusTetrahymena

Abstract

A holotrichous ciliate found repeatedly in very large numbers in the body cavity of larval midges(Chironomus plumosus)from Paris and Berlin areas is described as a new species of the genusTetrahymena, namedT. chironomisp.nov. It appears to represent a true example of facultative parasitism, since parasites released from the host survive in laboratory cultures, and free-living ciliates believed identical have been isolated from fresh-water sources in nature. Over a 3-month period more than 2000 larvae, principally fourth-instar stages, were examined; about 9 % of these were found to be infected with ciliates.T. chironomiis the thirteenth species to be added to the growing holotrich hymenostome genusTetrahymena.It is taxonomically distinguishable from other members of the genus on the basis of a combination of characteristics related to its morphology and bionomics. It is one of the smallest species, has 24–27 ciliary meridians and a relatively large, spherical micronucleus, does not exhibit dimorphism or cystic stages in its life cycle, and does not possess a caudal cilium.