Psammonobiotus dinarica Baković and Siemensma, 2023
Diagnosis: Shell is bilaterally symmetrical, in dorsal and ventral views spherical to ovoid in outline and in lateral view compressed with a length/height ratio of about 2:3. A funnel-shaped collar extends from a kidney-shaped oral aperture. In lateral view, the angle of the plane of this pseudostome collar is usually zero degrees, but can sometimes be as high as 33°. The translucent and fragile organic shell is covered with small irregularly-shaped thin and flat quartz particles. Larger particles are located on the dorsal and distal part of the shell and smaller particles on the ventral side. The rim of the collar is covered with relatively large flat particles. The organic matrix is colorless to dark brown.
Dimensions: Length including the collar 45–54 μm; main body width 26–30 μm, height 17–30 μm; collar 20–29 μm across (n=6).
Habitat: Freshwater, in cave sediment. Type locality: Croatia, Lika region, Lipovo polje, Dražice ponor, 44°46’20.2″N, 15°11’10.6″E.
Differential diagnosis. There are several testate amoebae similar in shape and size to P. dinarica: Centropyxis platystoma, Psammonobiotus communis, P. septentrialis and P. minutus, some Centropyxiella and Corythionella species, and Conicocassis pontigulasiformis. Centropyxis platystoma was described by Penard in 1890, but in 1902 he considered this species identical to Leidy’s C. constricta (Penard, 1890, 1902). Since he originally described it as Difflugia platystoma, the shell must have looked to him as that of a Difflugia, with a dense covering of quartz particles. Penard described the shell as “pierreuse”, stony. This is different from P. dinarica, where the shell is covered with tiny flat particles. In the original description, Penard showed a drawing of the visor with a strongly inwardly curved edge, in contrast to the edge of the collar of P. dinarica which is not curved. P. dinarica can be distinguished from P. septentrialis and P. minutus by its larger size, 45–54 μm long versus 10–12 μm and 23–30 μm, respectively (Golemansky 1970; Chardez 1977). The size is about the same as P. communis, 45–54 μm (Golemansky 1967) versus 33–52 μm, but P. dinarica can be distinguished from the latter by the kidney-shaped aperture. P. dinarica also bears some resemblance to Conicocassis pontigulasiformis, but this species is much larger, 82–90 μm, and the test wall has a much more pronounced granular organic cement and a circular aperture (Nasser and Patterson 2015). P. dinarica can be distinguished from Centropyxiella arenaria by its kidney-shaped aperture, and from C. elegans and C. lucida by its smaller size, length 45–54 μm versus 70–80 μm and 70–81 μm, respectively (Golemansky and Todorov 2007). It can be distinguished from similarly shaped Corythionella species (Golemansky 1970b) by the presence of small elliptical or oval idiosomes in the latter genus.