From Fensome et al., 2019:
Cleistosphaeridium tenuifilum Cookson and Eisenack, 1982, p.40, pl.8, fig.14. Holotype: Cookson and Eisenack, 1982, pl.8, fig.14. NOW Impletosphaeridium?. Originally Cleistosphaeridium, subsequently (and now) Impletosphaeridium?. Age: Paleocene.

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Original description: [Cookson and Eisenack, 1982] (translated from German):

Cleistosphaeridium tenuifilum n. sp.
Plate 8, Fig. 14

Type: The specimen shown on Plate 8, Fig. 14 and preserved in specimen Rivernook 26.
Diagnosis: Shell spherical, with numerous, very thin appendages that are briefly forked at the end.
Dimensions: Spherical shell approximately 71 μ, total approximately 90 μ; appendages up to approximately 17 μ.
Note: Given the thinness of the appendages, it is difficult to determine whether they are hollow.
Distribution: Rivernook Beds, Victoria; Paleocene.
Distinguished from other species of the genus Cleistosphaeridium by its very thin appendages.