Helicosphaera seminulum lophota Bramlette & Sullivan 1961
This helicolith features a symmetrical blanket that partly covers the distal surface of the flange (Type I, Helicosphaerella ampliaperta type). The flange termination varies among species, being either flush (e.g., Helicosphaeroides lophotes), expanded (e.g., Helicosphaeroides magnifica) or truncated (e.g., Helicosphaeroides watkinsii).
The bar structure spanning the central opening of the proximal plate may be conjunct, as in Helicosphaeroides mullerae, or disjunct, as in Helicosphaeroides lophotes. The central opening is featureless in some species, such as Helicosphaeroides ampliaperta.
In some species, the proximal plate lacks any distinguishable structure, as seen in Helicosphaeroides magnifica. Table 8 in Varol (2025) presents an overview of Helicosphaeroides species.
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.
Bramlette, M. N. & Sullivan, F. R. 1961, Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleontology 7(2): 129-188.
Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222