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)

These are medium to large species (typically 7-11 microns) with flanges that end in distinct wings. They are the most common helicoliths in most samples, but vary markedly through the Neogene. Forms with disjunct (optically discontinuous) bars (H. euphratis & H. intermedia) dominate in the Early Miocene but are replaced progressively by forms with closed central areas or conjunct bars. The blankets on these are initially rather chaotic (H. granulata) but forms with well ordered blankets with two in-line pores (H. carteri) become more common through the Late Miocene. In the Pliocene, forms with large and/or oblique pores (H. sellii and H. wallichii) become common.

Drawing	Outline description	Range
	H. euphratis - broad disjunct bar	NN1-3
	H. intermedia - narrow disjunct bar	NN1-11
	H. granulata - granular central area, without real pores	NN1-10
	H. carteri - pores inline	NN1-21
	H. wallichii - pores oblique	NN11(?)-21
	H. sellii - pores large	NN12-19
	H. inversa - pores separated by inversely oriented bar (points toward flange termination)	NN19-20
	H. pavimentum - small, narrow flange, inline pores	NN19-21