Helicosphaerella

Helicosphaera seminulum recta Haq, 1966

Coccolith has a helical flange, proximal plate and asymmetrical blanket ( Type II, Helicosphaerella recta type), which is birefringent under polarized light and partly covers the distal surface of the flange.

Blanket Type of Helicosphaerella: Asymmetrical blanket does not cover the entire distal surface of the flange (Type II, Helicosphaera recta type blanket).

Flange Termination:

• Rarely expanded flange termination as in Helicosphaerella gartneri
• Frequently flush flange termination as in Helicosphaerella compacta
• Often truncated flange termination as in Helicosphaerella truncata

Bar: a structure spanning the central opening

• Conjuct bar: formed from the elements of pelaga [optical continuation of pelaga] as in Helicosphaerella truncata
• Disjunct bar: disconnected from the pelaga (optically discontinuous) as in Helicosphaerella robinsoniae

The orientation of the bar:

• Inverse bar: diagonal bar having a frontal/anterior end at the side of flange termination as in Helicosphaerella theodoridisii (conjunct inverse). Helicosphaerella species with disjunct inverse bar is not observed.
• Traverse bar: bar aligned with the short axis of coccolith as in Helicosphaerella truncata (conjunct traverse) and Helicosphaerella wilcoxonii (disjunct traverse).
• Oblique bar: diagonal bar having a latter/posterior end at the side of flange termination as in Helicosphaerella compacta (conjunct oblique) and Helicosphaerella robinsoniae (disjunct oblique).

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.