Ultrastructure and geographic distribution of the genus Paradermamoeba (Gymnamoebia, Thecamoebidae)

Abstract

The genus Paradermamoeba includes two species with a distinct and unusually thick cell coat. This coat consists of densely packed helical glycostyles, up to 520 nm in length. Perhaps due to the impenetrable properties of the cell coat, we were unable to achieve satisfactory quality of EM fixation in these species until recently. In this study the treatment of cells with dilute Triton X-100 detergent prior to fixation has improved preservation of the ultrastructure of both Paradermamoeba species. Paradermamoeba valamo has an unusual central nucleolus consisting of densely packed fibrils of nucleolar material. A newly isolated strain of P. levis from a UK pond, Priest Pot, forms rounded, single-walled cysts. Both species have enigmatic trichocyst-like bodies in the cytoplasm. Despite the presence of a thick and highly differentiated cell coat, dictyosomes in both species are few and are not more developed than in many other species of gymnamoebae. Neither ultrastructure nor LM morphology indicates the phylogenetic position of Paradermamoeba. It seems that the family Thecamoebidae is a heterogeneous assemblage of unrelated genera. Recent isolation of both P. valamo and P. levis in Switzerland and in the UK indicates the wide distribution of both species in Europe.