Leptogromia operculata Valkanov 1970
Diagonosis: Shell pyrifom, organic, thin, hyaline and colorless, in cross-section broad elliptical; aperture rounded triangular, invaginated, with a small but distinct tube; cytoplasm doesn't fill the membrane completely; a globule, not a vacuole, is always present just above the aperture in the narrowing cytoplasm which moves through the aperture; nucleus large, ovoid, granular; filopodia branching and anastomosing, with bidirectional streaming of small granules; cytoplasm filled with food in the region of the aperture and with globules around the nucleus; vacuoles present near the aperture. The aperture is bordered by three flexible 'membranes' by which the aperture can be closed or opened.
Dimensions: 56-70 µm (n=18)
Ecology: Brackish and marine. Valkanov reported it from the Black Sea (salinity of 15-20 ). I sampled it from sediment in a small stream (2011) and a pond (2018), both with brackish water (salinity 13 ‰) on the island of Schiermonnikoog, in the northern part of the Netherlands.
Remarks: The most remarkable key characteristic is the globule which is always present in the cytoplasm just above the aperture. Also remarkable is the triangular shape of the aperture. However, Valkanov (1970) describes this as circular, but probably he has overlooked this small treat.