Adriamonas peritocrescens gen. nov., sp. nov., a new free-living soil flagellate (Protista, Pseudodendromonadidae Incertae Sedis)

The free-living Adriamonas peritocrescens, a new flagellate from calcareous pasture soil, has been studied by light microscopy and by scanning and transmission electron microscopy. The cell is elongate and possesses two anterior, subapically inserted subequal flagella. A mouth is situated in the antero-ventral part of the cell. Three flagellar roots, of which two are comprised of relatively few microtubules and one of many, arise from the flagellar basal bodies. Two of these roots, a major right and a minor left one, run parallel and posteriorly to the right under the ventral cell membrane. They both end in the lips of the mouth. The major root turns 180° around the opening of the mouth. The third root runs anteriorly and ends in an electron dense polar strip in the antero-dorsal part of the cell. This polar strip gives rise to a corset of microtubules, which lies under the dorsal surface. The cell has one or two concentric presumptive extrusomes and a contractile vacuole in the anterior part of the cell. Mitochondria have tubular cristae. A fragmenting nuclear envelope was observed during mitosis. Adriamonas peritocrescens has minimum doubling times of 2–3 hours in dense pure cultures of Arthrobacter globiformis at pH 7.5 and 20°C. The ultrastructure reveals some affinities with the pseudodendromonads, although scales and a stalk are absent. Its phylogenetic position is discussed.