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).

Remarks:

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 clearly separatelineage 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 spannd 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