Cleistosphaeridium microcystum, (Bujak in Bujak et al., 1980), Lentin and Williams, 1981

Originally Tenua Eisenack, 1958, then Cleistosphaeridium, subsequently (and now) Sentusidinium

Holotype: Bujak in Bujak et al. 1980, pl.22, fig.2-3
Paratype: Bujak in Bujak et al. 1980
Locus typicus: Alum Bay, Isle of Wight, southern England
Stratum typicum: Late Eocene

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Original description as Tenua microcysta: [Bujak in Bujak et al., 1980, p. 88-89]:

Diagnosis:
Autocyst ovoidal, sometimes with two weakly developed antapical lobes.
Autophragm smooth to chagrinate with abundant processes. The processes are nontabular and are of constant length on a specimen, but vary in length intraspecifically. The processes are mostly expanded proximally, hollow, and are distally capitate or bifid. Occasional processes are solid or simple.
The archaeopyle is apical, tetratabular, and has well-developed accessory archaeopyle sutures between the precingular paraplates. The operculum is detached.

Dimensions:
Autocyst length (without operculum) = 28-36 µm, breadth = 24-34 µm. Process length is up to 6 µm.