When I had found Psammonobiotus linearis, I remembered these photomicrographs which I took a year before without paying any attention to the collar. The shells are very small, 14 µm in length, which is nearly half the length of the shells of Psammonobiotus linearis. The second photomicrograph shows a hyaline veil or collar. These shells were found in a sample from Crailoo.
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: