Microcorycia radiata (Brown, 1912) Hopkinson, 1919
Diagnosis: Upper test part flat, of slightly conical shape (not dome shaped as with other species) having a somewhat raised centre point, colorless, less frequently slightly yellowish. In dorsal view, round, surrounded by two concentric rings, from the centre of which 5-8 (rarely up to 10) lines irradiate. The external ring of the two concentric rings may also be missing. The lower test part is a flexible, thin, plicate, open at the bottom and colorless membrane, which can be highly contracted. The test is purely organic in composition.
Dimensions: Brown (1912): 24-30 µm, Badewitz (2004): mean=28.1 (23-39) µm, n=25; my results: 24-26 µm, n=40.
Ecology: Terrestrial species. Moss, sphagnum, moss located at the lower part of tree trunk and on a roof, xerophile moss. Europe, arctic North-America, Greenland.
Remarks: The cell body does not fill up the test. Cytoplasm is greyish and granulate. It contains small food particles as well as several vacuoles. Epipodia and pseudopodia are formed (Penard 1917). The cell is mononuclear. The nucleus has a diameter of 5-6 pm . It has a variable shape: hemispherical, oblong, compressed or oval and has got a central nucleolus (Penard 1917).
M. radiata can form a lobopodium, which enables it to move. However, locomotion is so slow that it can be detected only by observation over a longer period of time. A widely rotund pseudopodium can also be extruded.
Reproduction: Penard (1917) made drawings of individuals in their division stages. According to this, division is of the transverse type. Hallas (1975), too, observed division stages. He wrote on this: “The thee of the ‘new’ animal is apparently produced within the thee of the ‘old’. Thereafter it is extruded out with its distal part first – folded like an umbrella.” The contradiction in both authors’ observations cannot be resolved presently.
Encystment: M. radiata forms exocysts. Hallas (1975) described the process of encystment. It starts with the formation of a thin, elastic saccule that is connected with the test through the pseudostoma. Then the amoeba leaves the test and crawls into the saccule. The saccule is enclosed by a capsule made of a highly refringent material. Next a gelatine-like external mantle surrounding the saccule is deposited. The encysted amoeba forms another test. Hallas observed directly the process of the amoeba’s move into the saccule with subsequent formation of a capsule. However, the encysted amoeba was squeezed by gentle pressure out of the cyst for proof of the test formed. Hallas pointed out that the test of an amoeba squeezed out of a cyst may lack typical test features.
All from Badewitz, 2004
