Nannotax

Description: Coccoliths circular to elliptical, central-area open or closed; central area grill delicate, but quite often preserved.

Remarks: Coccoliths are assigned to Reticulofenestra on the basis of absence of distinguishing features, consequently the genus is certainly highly paraphyletic and possibly polyphyletic.

Species: The rather simple morphology of Reticulofenestra makes subdivision into species notoriously problematic. The conventional taxonomy, as summarised in the table is primarily based on size, this is unstisfactorily arbitrary, but of stratigraphic value, especially since there are two distinct extinctions of larger Reticulofenestra; within NN10 and at the end of NN15 - see Young (1990) for details and discussion of species concepts. There are also a few distinctive short ranging species (e.g R. rotaria, R. calicis).

	Species	Range	Size and distinguishing features
	R. pseudoumbilicus	NN4-15	>5µm, (or >7µm)
	R. haqii	NN2-15	3-5µm
	R. minutula	NN15-19	3-5µm with a few (up to 5) slits in the distal shield
	R. minuta	Eocene-NN19	3-5µm without slits in distal shield
	R. rotaria	NN11	5-7µm circular with wide central area
	R. calicis	NN15	2.5-5µm with tube extended to form cup-like structure
	R. asanoi	NN19	>6.5µm sub-circular to broadly elliptical
	R. sessilis	NN21	2-4µm with close cenral area, associated with diatom
	R. bisecta	Eocene-NN1	8-12µm with closed central area
	R. daviesii	Oligocene-NN2	5-8µm, with plug in central-area surrounded by narrow ring of pores.

Synonym: Dictyococcites Black, 1967 - like Reticulofenestra but with closed central-area.