I found this one in a sample from the Bert Bospad, the Netherlands. It came up in a wet mount kept in a moist chamber for some days. There was one specimen, attached to the underside of the coverslip. It had granules in its filopodia and showed moving and running plasmveils The granules are few in number, but distinct. It was impossible to detect the shape and structure of the pseudostome and the nucleus. The body is spherical.
M. ovalistoma – after Bartos, 1963 Metaheleopera Bartos, 1963 Diagnosis: Shell clearly narrowing towards the pseudostome, which can be seen even more clearly on the narrower sides
M. radixicola – after Chardez, 1974 Matsakision radixicola Chardez, 1974 Diagnosis: Shell ovoid, slightly compressed, transparent; pseudostome oval, truncated perpendicularly, with a slight neck. Shell
M. cassagnaui – after Bonnet, 1967 Matsakision cassagnaui Bonnet, 1967 Diagnosis: Shell hyaline, elongated ovoid, very little compressed, truncated perpendicularly or very slightly obliquely in
Matsakision – after Bonnet, 1967 Matsakision Bonnet, 1967 Diagnosis: Shell hyaline, elongated ovoid, very little compressed, truncated perpendicularly or very slightly obliquely in the region
Arcella marginata, after Deflandre, 1929 Arcella marginata Daday, 1905 Diagnosis: Shell roughly hemispherical, rather overhanging, with a flattened, smooth edge. In dorsal view showing a
Arcella lobostoma, after Deflandre, 1929 Arcella lobostoma Deflandre, 1929 Diagnosis: Shell hemispherical. In ventral view, irregular circular outline, often a little elliptical; pseudostome irregularly lobed: