Helicosphaera carteri

Nannotax Commentary on Helicosphaera carteri

Varol (2025) proposed restricting the name H. carteri to specimens exhibiting very large pores, arguing that the holotype displays this morphology. However, the type illustration of Wallich (1877) is schematic and depicts only the central area of the coccolith, rendered under bright-field rather than cross-polarised light (XPL). See also Young (1998, p. 236).

Several points challenge this interpretation:

A schematic drawing does not necessarily misrepresent the proportions of the specimen.

Different illumination modes — bright field, phase contrast, or cross-polarised light — do not produce notable differences in apparent pore size (see examples below).

Nevertheless, Helicosphaera carteri must be restricted to large-pore specimens in order to remain consistent with the holotype.

Species Known to Possess Large Pores

Helicosphaera inversa — The bar shows no inversion whatsoever. Restricted to NN21, Chibanian (0.13–0.29 Ma). This species is considered invalid and is a synonym of Helicosphaera carteri.

Helicosphaera sellii — Restricted to NN19, Calabrian, through NN11, Tortonian (1.26–5.6 Ma). This leaves a stratigraphical gap of nearly one million years with Helicosphaera inversa above, and over five million years with Helicosphaera bownii below.

Helicosphaera bownii — Restricted to NN7, Tortonian, through NN4, Langhian (11.42–15.99? Ma).

These species may be treated as synonymous on morphological grounds or maintained as distinct species given the age gaps between their stratigraphical ranges.

Note: Helicosphaera mediterranea has been excluded from the above discussion, as it is distinguished from all the above forms by a conspicuous suture running parallel to the long axis on the conjunct bar.