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Habibacysta sp.
Habibacysta? sp. of Head 1994
Figured in Head 1994: Plate 9, figs.8-12; Plate 10, figs. 1-12; Plate 11, fig. 13; text-figure 3.
Description: Head 1994, p. 306
Cysts are spherical, with numerous low rounded bumps over the surface. The pedium is thin and solid, bearing columellae of about 0.2-0.3Ám diameter that are about 1.0 to 2.0Ám apart, although fusion between some adjacent columellae occurs on all specimens. The tegillum, supported by the columellae, is smooth and extremely thin, becoming thicker where it rises to form bumps, and may be perforate. The archeopyle is precingular formed by loss of paraplate 3". The archeopyle margin is smooth and angles are rounded. There are no accessory sutures. The operculum is free. There is no other expression of paratabulation.
Dimensions: Diameter: 29(33.6)38Ám. Wall thickness about 1.0Ám to 1.5Ám. Eight uncompressed specimens were measured.
Discussion: Head 1994, p. 306
Habibacysta? sp. differs from Habibacysta tectata in having low (0.5,um or less high) bumps on the surface. In optical section, slight thickening of the tegillum at bumps is apparent, and SEM observation of a single specimen (Plate 11, fig. 13) shows perforations occurring between bumps but not over them (see also text-figure 3). Even between bumps the tegillum is less perforated than for Habibacysta tectata. Specimens of Habibacysta? sp. are provisionally assigned because whereas they have the tegillate/columellate wall typical of Habibacysta they also possess low bumps suggestive of rudimentary processes. A morphotype of Operculodinium centrocarpum sensu Wall and Dale 1968b, characterized by a columellate/tegillate wall and fibrous processes, is common in all Coralline Crag samples (Plate 11, figs. 14, 15). Wall structure, central body size, and shape of archeopyle compare closely with specimens here assigned to Habibacysta? sp. Furthermore, specimens of Operculodinium centrocarpum sensu Wall and Dale 1968b bearing processes reduced to low bumps are reported in the literature (e.g., Turon and Londeix 1988, pl. 4, figs. 6-8). On balance, Habibacysta? sp. is possibly an end member of the columellate/tegillate morphotype of Operculodinium centrocarpum sensu Wall and Dale 1968b, hence the approach not to name it formally as yet. More work is necessary to fully document the range of morphologic variability in Operculodinium centrocarpum sensu
Wall and Dale 1968b in the Coralline Crag samples.
Occurrence in eastern England: Mid Pliocene Coralline Crag (about 3.55-3.75 Ma), Rockhall Wood, Sutton, all four samples from lithological Unit B (Balson and Long in Gibbard and Zalasiewicz 1988, p. 66-71; Balson 1990).
Other records: There are no other known occurrences of Habibacysta? sp.
Figured in Head 1994: Plate 9, figs.8-12; Plate 10, figs. 1-12; Plate 11, fig. 13; text-figure 3.
Description: Head 1994, p. 306
Cysts are spherical, with numerous low rounded bumps over the surface. The pedium is thin and solid, bearing columellae of about 0.2-0.3Ám diameter that are about 1.0 to 2.0Ám apart, although fusion between some adjacent columellae occurs on all specimens. The tegillum, supported by the columellae, is smooth and extremely thin, becoming thicker where it rises to form bumps, and may be perforate. The archeopyle is precingular formed by loss of paraplate 3". The archeopyle margin is smooth and angles are rounded. There are no accessory sutures. The operculum is free. There is no other expression of paratabulation.
Dimensions: Diameter: 29(33.6)38Ám. Wall thickness about 1.0Ám to 1.5Ám. Eight uncompressed specimens were measured.
Discussion: Head 1994, p. 306
Habibacysta? sp. differs from Habibacysta tectata in having low (0.5,um or less high) bumps on the surface. In optical section, slight thickening of the tegillum at bumps is apparent, and SEM observation of a single specimen (Plate 11, fig. 13) shows perforations occurring between bumps but not over them (see also text-figure 3). Even between bumps the tegillum is less perforated than for Habibacysta tectata. Specimens of Habibacysta? sp. are provisionally assigned because whereas they have the tegillate/columellate wall typical of Habibacysta they also possess low bumps suggestive of rudimentary processes. A morphotype of Operculodinium centrocarpum sensu Wall and Dale 1968b, characterized by a columellate/tegillate wall and fibrous processes, is common in all Coralline Crag samples (Plate 11, figs. 14, 15). Wall structure, central body size, and shape of archeopyle compare closely with specimens here assigned to Habibacysta? sp. Furthermore, specimens of Operculodinium centrocarpum sensu Wall and Dale 1968b bearing processes reduced to low bumps are reported in the literature (e.g., Turon and Londeix 1988, pl. 4, figs. 6-8). On balance, Habibacysta? sp. is possibly an end member of the columellate/tegillate morphotype of Operculodinium centrocarpum sensu Wall and Dale 1968b, hence the approach not to name it formally as yet. More work is necessary to fully document the range of morphologic variability in Operculodinium centrocarpum sensu
Wall and Dale 1968b in the Coralline Crag samples.
Occurrence in eastern England: Mid Pliocene Coralline Crag (about 3.55-3.75 Ma), Rockhall Wood, Sutton, all four samples from lithological Unit B (Balson and Long in Gibbard and Zalasiewicz 1988, p. 66-71; Balson 1990).
Other records: There are no other known occurrences of Habibacysta? sp.