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Cleistosphaeridium spinulastrum

Cleistosphaeridium spinulastrum, Islam, 1983

Holotype: Islam, 1983, pl.2, fig.1
Locus typicus: Hampshire Basin, S England
Stratum typicum: Middle Eocene

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Original description: [Islam, 1983, p. 337-338]:

Diagnosis:
Cyst subspherical and skolochorate with chagrinate surface; numerous nontabular, elongate conical processes of more or less half cyst diameter in length, hollow, closed at both ends, tapering from broad circular bases to narrow solid necks and acuminate, entire or rimmed distal tips; pairs of processes frequently proximally joined;
paracingulum not indicated;
archeopyle apical type tA.

Dimensions:
Holotype: cyst body 28 x 38 µm (without operculum), length of processes 10-13 µm.
Range: cyst length 33(28)23 µm, breadth 38(31)26 µm, length of processes 10-17 µm. Specimens measured: 7.

Affinities:
This species differs from others of the genus in process morphology by which it resembles Diphyes spinula but differs in lacking the distinctively broad antapical process. It also resembles Dapsilidinium pastielsii (Davey and Williams) Bujak et al. 1980 but differs in possessing distally closed processes. However, C. spinulastrum n. sp. and D. pastielsii are morphogenetically related through transitional forms, but the former could not be referred to Dapsilidinium Bujak et al. 1980, as the genus is characterized by distally open processes while the generic circumscriptions of Cleistosphaeridium readily accommodated the species. Cleistosphaeridium spinulastrum, is also stratigraphically significant and younger.
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