Rhabdospora thelohani Laguessé, 1895 (Apicomplexa): New Host and Geographic Records with Taxonomic Considerations*

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Abstract
New fish species and geographic records for R. thelohani Laguesse, 1895 (rodlet cells) are presented. The ultrastructure of R. thelohani in Alburnoides bipunctatus ohridanus Karaman, Borostomias antarcticus (Loennberg), Leuciscus cephalus albus Bonaparte and Rutilus rubilio (Bonaparte) is compared with other reports and with members of subphylum Apicomplexa. The ultrastructure of R. thelohani was similar in all fish species examined; the organism was not present in all members of any single species and had intertissue density variations. R. thelohani is pyriform, averaging in size 7 .times. 12 .mu.m, with a basal nucleus. The surface complex is composed of a layer (0.5 .mu.m diameter) formed by microfilaments (9.3 nm) and an outer trilaminar membrane (9.3 nm). The cytoplasm contains structures identical to rhoptries, micronemes and subpellicular microtubules. Mitochondria, Golgi apparatus and rough endoplasmic reticulum were not observed, although free ribosomes were present and arranged in a vesicular pattern. Observations suggest that the organism moves between cells of epithelial layers and is either released into a lumen intact or passively or actively discharges its contents into a lumen. R. thelohani should be considered a member of Apicomplexa unless definitive evidence is presented to the contrary.