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Actinosphaerium nucleofilum
A. nucleofilum, Phase-contrast, Netherlands, 2020

Actinosphaerium nucleofilum Barrett, 1958

Diagnosis: Cell strongly vacuolated, ecto- and endoplasm not clearly differentiated. Diameter of endoplasm approximately the thickness of the ectoplasm. With small and numerous nuclei, 4-11 µm in diameter, with peripherally located nucleoli and with a cyst wall incorporating spherical siliceous elements. Axopodia approximately twice as long as the cell diameter. Cells can adhere so strongly to the substrate that they cannot be aspirated with a micro pipette!

Dimensions: Cell body 45-700 µm, average 200-400 µm. My measurements 230-400 µm; nuclei 4-11 µm.

Ecology: Freshwater. North-America (Barrett, 1958) and Europe (Netherlands, Siemensma, 1981 and 2020)

Remarks: Barrett (1958) distinguished this species from A. eichhornii, because in A. nucleofilum the axopodia terminate on the surface of a nucleus or in their immediate vicinity, and the nucleolar material is located peripherally. The diameter of the nuclei is relatively small. Cysts have spherical siliceous elements in the wall (Patterson and Thompson 1981).

Actinosphaerium nucleofilum
A. nucleofilum, somewhat compressed by the cover glass, Netherlands, 2020
Actinosphaerium nucleofilum
A. nucleofilum, some nuclei arrowed; approximately 30 nuclei visible. Netherlands, 2020
Actinosphaerium nucleofilum
A. nucleofilum, nuclei; notice the difference in size.
Actinosphaerium nucleofilum
A. nucleofilum, Phase-contrast, Netherlands, 2020
Actinosphaerium nucleofilum
A. nucleofilum, Phase-contrast, Netherlands, 2020

Actinosphaerium nucleofilum
Actinosphaerium nucleofilum – a habitus; b nucleus – Ferry Siemensma, 1991
Actinosphaerium nucleofilum
Actinosphaerium nucleofiluma specimen with strongly bend axopodia; b detail; c specimen with preyed rotifer; d A. eichhornii compared with e A. nucleofilum – drawing Ferry Siemensma, 1991
Actinosphaerium nucleofilum
Habitat of A. nucleofilum, Gooimeer, Netherlands, 2020
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