Difflugia microclaviformis (Kourov, 1925)
Diagnosis: test pyriform, usually with a distinct aboral protuberance; test circular in cross-section, colorless to brown, usually composed of small to medium pieces of quartz; smooth surface and a well defined outline; protuberance often eccentrically placed; neck sometimes slightly bent; pseudostome circular, surrounded by small particles; zoochlorellae observed; nucleus spherical, with ring-shaped nucleolar material scattered through the nucleus.
Dimensions: Kourov 185 µm; Ogden 202-206 µm (n=2); my measurements: 151-186 µm (n>30).
Ecology: in sediments of ditches.
Remarks: shells of Difflugia microclaviformis seem to be rare. I found this species only in the sediment of two ditches with Sphagnum contact in the nature reserve Naardermeer (north and south) in the Netherlands. Specimens on both locations were abundant and alive. Between the typical specimens, with protuberances, also specimens with a smooth fundus were present (see the photo below).