Nannotax Enabling nannofossil research

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.

	H. euphratis - broad disjunct bar	NN1-3
	H. intermedia - narrow disjunct bar	NN1-11
	H. granulata - granullar 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

The principal morphological division is between the forms with a disjunct bar and the others. This forms a convenient means of dividing the lineage. It is nonetheless somewhat arbitrary, since many H. granulata type specimens have partially discontinuous central areas, and no other feature parallels the division.