Ultrastructure of the heterotrophic flagellates Cyathobodo sp., Rhipidodendron huxleyi Kent, 1880, Spongomonas sacculus Kent, 1880, and Spongomonas sp

Four free-living, heterotrophic flagellates from dystrophic bog lakes in Northern Germany were examined by light and electron microscopy: Cyathobodo sp., Rhipidodendron huxleyi, Spongomonas sacculus, and Spongomonas sp. In general morphology and in ultrastructure Cyathobodo sp. is a typical member of its genus: it is triangular in shape, colourless and stalked. One contractile vacuole is anterior-medially situated. The single nucleus is dorsally located and always associated with the basal bodies of the two flagella, the Golgi apparatus and a tubulocristate mitochondrion. Two microtubular roots that support the cytopharynx with their distal parts arise from the flagellar apparatus. Cyathobodo sp. differs from the other described species of the genus in the absence of body scales. It has a theca instead which suggests a reduction of the scales. Rhipidodendron huxleyi, Spongomonas sacculus and Spongomonas sp. belong to the family Spongomonadidae. This family comprises free-living, colonial, heterotrophic flagellates, embedded in an organic matrix with brownish matrix spherules. Their mode of nutrition remains unresolved, since neither structures for food uptake nor definite food vacuoles were observed. The ultrastructure of their flagellar apparatuses closely resembles that of previously described species. All three described species contain en-dosymbiotic bacteria which may be involved in the formation or degradation of the matrix spherules.