Nannotax Enabling nannofossil research

Description: Coccoliths with helical flange, sub-groups can be recognised based on presence/absence of a disjunct bar, bar orientation, flange shape, etc. (see e.g. Theodoridis 1984, Perch-Nielsen 1985b, Aubry 1990, Young 1998).

Type: Helicosphaera carteri

Synonym: Helicopontosphaera

Subdivision: The large number of described species have been variously subdivided into sub-groups by different workers (e.g. Aubry 1990, Theodoridis 1984). The subdivision followed here is essentially based on Young (1998). The recta group appears to be a clearly separate lineage from the other Helicosphaera species, but the phylogenetic unity of the walbersdorfensis and ampliaperta groups is less certain.

	Helicosphaera carteri group - typical forms	NPX-NN21
	Helicosphaera ampliaperta group - with open central area, sometime spanned by narrow bar	NP21-NN4
	Helicosphaera recta group - with flange abruptly terminated and inversely-oriented pores/bar	NP23-NN11
	Helicosphaera walbersdorfensis group - small, with flange extending unusually far round coccolith, normally-oriented oblique pores	NN2-NN11

Drawings - the drawings used in the table above are from Theodoridis (1984)