Helicosphaeroides

Helicosphaera seminulum lophota Bramlette & Sullivan 1961

Coccolith has a helical flange, proximal plate and symmetrical blanket which is birefringent under polarized light and partly covers the distal surface of the flange (Type I, Helicosphaeroides ampliaperta type blanket).

Blanket Type of Helicosphaeroides: Symmetrical blanket that partly covers the distal surface of the flange (blanket does not reach the periphery of the flange or confined the central area). Type I, Helicosphaeroides ampliaperta type blanket).

Flange Termination:

• Often expanded flange termination as in Helicosphaeroides magnifica
• Frequently flush flange termination as in Helicosphaeroides seminulum
• Rarely truncated flange termination as in Helicosphaeroides watkinsii

Bar: a structure spanning the central opening

• Conjuct bar: formed from the elements of pelaga [optical continuation of pelaga] as in Helicosphaeroides crouchii
• Disjunct bar: disconnected from the pelaga (optically discontinuous) as in Helicosphaeroides seminulum

The orientation of the bar:

• Inverse bar: diagonal bar having a frontal/anterior end at the side of flange termination as in Helicosphaeroides bowmanii (conjunct inverse). Helicosphaerella species with a disjunct inverse bar is not observed.
• Traverse bar: bar aligned with the short axis of coccolith as in Helicosphaeroides crouchii (conjunct traverse) and Helicosphaeroides seminulum (disjunct traverse).
• Oblique bar: diagonal bar having a latter/posterior end at the side of flange termination as in Helicosphaeroides waltrans (conjunct oblique) and Helicosphaeroides lophotes (disjunct oblique).

The definition of Helicosphaeroides is amended to include helicoliths with the symmetrical blanket that partly covers the distal surface of the flange (blanket does not reach the periphery of the flange or confined the central area). This amendment is consistent with the holotype. The presence or absence of a bar is not used for diagnostic criteria.

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.