Difflugia lacustris (Penard, 1899)
Diagnosis: shell transparent, colorless; elongated ovoid with a long, thin neck that makes up about half of the shell length; shell composed of a mixture of flattish pieces of quartz, fragments of diatom frustules and some small siliceous plates; usually the neck has an encrustation of thicker quartz particles just anterior to the junction with the body. Small isolations of organic cement, in the form of small rings, are sometimes seen. Aperture circular and surrounded by small pieces of quartz.
Dimensions: Ogden 140-231 µm. My measurements: 131-205 µm.
Remarks: This seems to be an "easy" species to recognize, but it closely resembles Difflugia bryophila from which it is possibly indistinguishable. Just look here!