Actinosphaerium arachnoideum Penard, 1904

Diagnosis: Body 50-90 µm. Ectoplasm with large vacuoles; endoplasm granulated with small vacuoles. Up to 12 nuclei, usually less than 6. Diameter of nucleus up to 12 µm. Nucleus with many small nucleoli. Axopodia long, up to four times the body diameter, anastomosing and sometimes smooth like filopodia.

Remarks: I found many specimens that resembled this species in a dune lake near Bakkum, the Netherlands, 2022. They all had long axopodia and their nuclei were filled with granular nucleolar material. The nuclei were not numerous and 13.2-13.8 µm in diameter, a little larger than those described by Penard.