Observations on Pyxidium tardigradum (Ciliophora), a protozoan living on Eutardigrada: infestation, morphology and feeding behaviour
Pyxidium tardigradum is a protozoan that has been reported on a few occasions as an epizoan symphoriont living on eutardigrades. We report here the first records of this species from Kirghizia (the first Asian record), Poland and Portugal. The Portuguese population revealed the largest P. tardigradum infestation ever described in terms of both the whole tardigrade population, with 60% affected animals, as well as a single host, with 35 attached protozoan. The first ever Scanning Electron Microscope (SEM) photomicrographs and pictures of live P. tardigradum are also given. No considerable ultrastructural variability was detected within or between the populations, suggesting that P. tardigradum may be a true cosmopolitan species. Given that the ciliate imposed significant extra volumes on infested tardigrades (from 1% to as much as 136%), we also discuss possible negative effects of the protozoan on the fitness of the host and suggest that P. tardigradum should probably be considered as a eutardigrade parasite. Furthermore, some hypotheses about the life history strategies of the ciliate are proposed.
KeywordsBody Volume Moss Sample Portuguese Population Host Size Lichen Sample
The kind help of Dr. Gabriel Martins (University of Lisbon) in obtaining pictures of live specimens is greatly appreciated. We are also grateful to Dr. Matt Gage (University of East Anglia) for the valuable comments on the manuscript.
The study was partially supported by a grant to ŁM & ŁK from the European Commission’s (FP 6) Integrated Infrastructure Initiative programme SYNTHESYS (grant no. DK-TAF-2576). Parts of this paper describing the first SEM observations of P. tardigradum were presented by ŁM & ŁK at the 10th International Symposium on Tardigrada in Catania, Italy, 18th–23rd June 2006.
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