Fisculla terrestris (Dumack, Müller et Bonkowski, 2016) comb. nov.
Diagnosis: Colorless, testate amoebae. Test round or pyriform, colorless, hyaline, highly flexible, due to ingested material maybe deformed. Nucleus vesicular, usually located in the apical end of the cell. Nucleolus spherical, central to nucleus. Locomotion: actively creeping with filopodia (which may anastomose and rarely extend longer than 60 µm); inactively by floating forms, these are formed during digestion and under unavailability of food material, the cytoplasm of starving cells shrinks during starvation. Cell aggregates: formed in older cultures with decline of food density, regular (concentric arrangement of cells where every fused cell retains its nucleus and cell shape) or irregular (deformed cells that lead to one big test enclosing several nuclei). Size depends on the number of fused individuals (usually < 7 rarely more). Cell division: longitudinal, binary.
Dimensions: Test length 12-17 µm, width 10-16 µm, L/W ratio 1-1.27; nucleus about 4.5 ± 0.2 µm, nucleolus about 2.1 ± 0.1 µm.
Ecology: Feeding on immobile, unicellular fungi and algae < 25 µm; no ingestion of bacteria observed. Prey gets ingested by a siphon-like pseudopodium, highly flexible and expandable (< 20 µm).
Remarks: in 2015 I got a culture from Kenneth Dumack. I kept some specimens in a wet mount for several weeks (in a moist chamber) and in the end a number of very large multinucleate specimens could be observed, see photomicrographs below.