Nannotax

Description: Ubiquitous species, often forming blooms. Coccospheres often with multiple layers of coccoliths.

Remarks: The open structure of E. huxleyi coccoliths makes them highly vulnerable to both overgrowth and etching.

Range: NN21

Variability of extant E. huxleyi 

Well-established morphotypes: Young & Westbroek (1991) distinguished four types (A, B, C & corona) based on heterococcolith morphology, see also van Bleijswijk et al. (1991) and Young (1994). Medlin et al. (1996) consider these types should be regarded as separate varieties, their recommended names are given in brackets, (). Additonal recently recognised are type R and type B/C (Young et al. 2003). It should be noted that further variation is seen in degree of calcification, leading to variable central area closure and slitting of proximal shield.

	Type A (huxleyi)	liths medium -sized (3-4 µm), distal shield elements robust, central area elements curved
	Type B (pujosiae)	liths large (3.5-5 µm), distal shield elements delicate, central area elements irregular laths. Proximal shield often wider than distal shield. Similar large E. huxleyi forms have been recognised in the fossil record and are regarded by some authors as cold-water forms.
	Type C (kleijneae)	liths small (2.5-3.5 µm), distal shield elements delicate, central area open or covered by thin plate.
	Type B/C	Liths medium-sized, (3-4 µm), distal shield elements delicate, i.e. similar in morphology to types B & C, but intermediate in size. This form often dominates assemblages in the Southern Ocean (Hockfield 2000; Findlay & Giraudeau 2000, referred to as type C).
	E. huxleyi var. corona (Okada & McIntyre 1977) Jordan & Young 1990	Like type A, but with inner tube cycle forming discontinuous elevated crown around central area.
	Type R	Like type A, but with heavily calcified shield elements, indeed slits often closed giving a Reticulofenestra-like appearance (hence designation as type R). Several specimens of this form have been isolated from the S.W. Pacific and they have maintained their distinctive morphology for several years indicating that this is stable genotypic variation (Probert, Young unpubl. obs). Similar morphotypes were observed in the same area by Nishida (1979) and Burns (1977)