Revision of the Family Spironemidae Doflein (Protista, Hemimastigophora), With Description of Two New Species, Spironema Terricola N. Sp. and Stereonema Geiseri N, G., N. Sp.

<jats:p><jats:bold>ABSTRACT.</jats:bold> Two new hemimastigophoran flagellates are described using light and electron microscopy, and the family Spironemidae is revised. <jats:italic>Spironema terricola</jats:italic> n. sp. occurs in soil from the Grand Canyon (southwest USA). It moves in a conspicuously euglenoid manner and differs from <jats:italic>S. multiciliatum</jats:italic> Klebs by its vermiform shape and shorter kinetics. <jats:italic>Spironema terricola</jats:italic> is similar to Goodey's <jats:italic>Spironema multiciliatum</jats:italic> from soil in England. However, Goodey's vermiform species has a very elongate nucleus and is thus neither identical with <jats:italic>S. terricola</jats:italic>, which has a roundish nucleus, nor with Klebs' lanceolate <jats:italic>S. multiciliatum</jats:italic>; we consider it a new species, <jats:italic>Spironema goodeyi</jats:italic> n. sp, <jats:italic>Stereonema geiseri</jats:italic> n. g., n. sp. was discovered in the Aufwuchs (periphyton) of a river in Bavaria, Germany. the new genus differs from <jats:italic>Spironema</jats:italic> by its a contractility, and from <jats:italic>Hemimastix</jats:italic> by its shorter kinetics and less plicate cortex. the fine structure of <jats:italic>Spironema</jats:italic> and <jats:italic>Stereonema</jats:italic> is very similar to that of <jats:italic>Hemimastix</jats:italic> Foissner et al., viz., the cortex is composed of two plates having diagonal symmetry and the flagellated basal bodies have associated a short and a long microtubular ribbon. All species have unique extrusomes of the same type. the main differences between the three genera and five species recognized are contractility, length of kinetics, body size, shape of cell and nucleus, and particulars of the cortex and extrusomes. the phylogenetic relationships of the Hemimastigophora are still uncertain. However, the diagonal symmetry of the cortical plates and the pronounced euglenoid movement of <jats:italic>Spironema</jats:italic> spp. suggest a common ancestor with euglenids.</jats:p>