From Fensome et al., 2019:
Spiniferites ramosus ssp. gracilis (Davey and Williams, 1966a, p.34–35, pl.1, fig.5; pl.5, fig.6) Lentin and Williams, 1973, p.130. Holotype: Davey and Williams, 1966a, pl.5, fig.6; Bujak et al., 1980, pl.4, figs.1–2. Originally Hystrichosphaera ramosa var. gracilis, subsequently Spiniferites ramosus var. gracilis, thirdly (and now) Spiniferites ramosus subsp. gracilis. Lentin and Williams (1993, p.614) retained this taxon as Spiniferites ramosus subsp. gracilis. Taxonomic junior synonym (at subspecific rank): Hystrichosphaeridium plicatum, according to Sarjeant (1983, p.93). Age: Cenomanian–Eocene.

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Locus typicus: Sheppey, Kent, England
Stratum typicum: Eocene

Original diagnosis: Davey and Williams, 1966, p. 34: Hystrichosphaera ramosa ssp. gracilis
A variety of H. ramosa (Ehrenberg) with smooth, thin-walled central body bearing gonal and sutural processes. Processes solid or hollow and relatively long and slender. Crests proximal and extending along all processes often as far as the trifurcation. Gonal processes mainly trifurcate, sutural processes bifurcate, all but smallest terminating with small trifurcation.
Dimensions:
Holotype: diameter of central body 35 by 43 µm, length of processes 17-23 µm.
Range of London Clay specimens; diameter of central body 32-61.5 µm.
Length of processes up to 29 µm.