Coccosphaera carterii Wallich, 1877
Helicopontosphaera Hay & Mohler 1967
A helicolith features a symmetrical blanket that entirely covers the flange’s distal surface (Type III, Helicosphaera carteri type). The flange termination varies among species, being expanded (e.g., Helicosphaera carteri) or truncated (e.g., Helicosphaera acuta).
The bar structure spanning the central opening of the proximal plate may be conjunct, as in Helicosphaera bownii, or disjunct, as in Helicosphaera intermedia. The proximal plate lacks any distinguishable structure in some species, as seen in Helicosphaera burkei. The orientation of the bar is a key distinguishing characteristic among Helicosphaera species:
• Inverse bar: A diagonal bar with its anterior (front) end positioned at the side of the flange termination, as seen in Helicosphaera acuta (conjunct inverse). Helicosphaerakilida exhibits an inverse disjunct bar.
• Transverse bar: A bar aligned with the short axis of the helicolith, as in Helicosphaera mediterranea (conjunct transverse) and Helicosphaera truempyi (disjunct transverse).
• Oblique bar: A diagonal bar with its posterior (rare) end positioned at the side of the flange termination, as observed in Helicosphaera wallichii (conjunct oblique) and Helicosphaera intermedia (disjunct oblique). An overview of Helicosphaera species is presented in Table 6.
Optical Properties: The proximal plate and the flange remain in constant extinction, while the blanket exhibits first-order interference colours with inclined extinction and length-fast (−) elongation.
Aubry, M. -P. & Bord, D. 2009. Reshuffling the cards in the photic zone at the Eocene/Oligocene boundary. In: Koeberl, C., Montanari, A. (eds), The Late Eocene Earth-Hothouse, Icehouse, and Impacts. Geological Society of America, Special Papers 452: 279-301.
Hay, W. W., Mohler, H. P., Roth, P. H., Schmidt, R. R., Boudreaux, J. E., 1967. Calcareous nannoplankton zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean area, and transoceanic correlation. Transactions of the Gulf-Coast Association of Geological Societies 17, 428-480.
Kamptner, E., 1954. Untersuchungen über den Feinbau der Coccolithen. Archiv für Protistenkunde 100, 1-90.
Wallich, G. C. 1877. Observations on the coccosphere. Annals and Magazine of Natural History 19: 342-350.