TAXONOMIC AND ECOLOGICAL CHARACTERIZATION OF STOMATOCYSTS OF SPUMELLA‐LIKE FLAGELLATES (CHRYSOPHYCEAE)1

Cyst formation is a characteristic feature of chrysophytes. Cyst morphology is used for species identification, and the distribution of cysts in sediment cores is used to infer past climate conditions. The affiliation of stomatocyst demes with morphospecies, however, remains unclear. Here, we investigated the taxonomic and ecological value of the occurrence of cyst formation and cyst morphology to differentiate chrysophyte flagellates of the Spumella‐morphodeme, which are among the numerically dominant eukaryotes in many aquatic and terrestrial habitats. In the investigated 90 strains of Spumella‐like flagellates, we observed encystment only in six strains despite the broad range of temperature regimes and chemical factors tested. Spumella‐like flagellates that produce cysts are affiliated with different subclusters within the Chrysophyceae and are closely related to strains for which cyst formation is not known. The occurrence of cyst formation is therefore unsuitable as a taxonomic criterion. Cyst morphology allows for differentiating some strains even though distinctly different strains may have similar or even identical‐looking cyst demes. Despite considerable changes in cell size of the vegetative cells related to the nutritional status, the size of the cysts was always larger than that of a typical vegetative cell. Cysts were colorless and had no chromatophores, and some granula were visible in the light microscope. None of the investigated strains and none of the so far published cyst descriptions of Spumella spp. entirely seem to match the cyst description of the generic type strain. However, taking methodological bias between light and electron microscopical investigations into account, the cysts 199hm (this paper) and N1846 (Yubuki et al. 2008) seem to correspond to the cyst of the generic type strain. We propose the strain 199hm as epitype for Spumella vulgaris Cienkowsky; we further describe Spumella rivalis Boenigk et Findenig sp. nov., Pedospumella encystans Boenigk et Findenig gen. et sp. nov., and Poteriospumella lacustris Boenigk et Findenig gen. et sp. nov.