Helenea staurolithina
Set number: 3107
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Set number: 3106
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Set number: 3108
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10µm
Helenea staurolithina Worsley, 1971
Microstaurus lindensis Black 1971a
Large (>6.0 µm), normally elliptical species (ellipticity 1.2–1.3) of Helenea are characterised by an axial cross that may be slightly rotated relative to the axis of the placolith. The arms of the cross have bifurcated terminations and support a short distal process with a distinct square-shaped termination.
The entire species exhibits first-order, slightly greyish-white interference colours. The pelaga of Helenea staurolithina exhibits inclined extinction and length-fast (-) elongation in its natural settling position, as seen in plan view under crossed polars.
Helenea staurolithina differs from Helenea chiastia in that it is larger than 6.0 µm. Worsley (1971) noted in the remarks section for Helenea staurolithina that “H. staurolithina is differentiated from H. chiasta by its larger size and greater number of elements in the distal rim”. However, the number of segments (elements) cannot be accurately determined using the light microscope.
Black, M. 1971a. Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society 38: 381-424.
Worsley, T. R., 1971. Calcareous nannofossil zonation of Upper Jurassic and Lower Cretaceous sediments from the Western Atlantic. In: Farinacci, A. (ed.), Proceedings of the Second Planktonic Conference Roma 1970. Edizioni Tecnoscienza, Rome vol. 2, pp. 1301-1321.