Nannotax3 - Coccolithophores - Coccolithophores

Citation: Coccolithophores informal

Rank: overall group

Notes & discussion: Coccolithophore classification is primarily based on the calcareous coccoliths they produce. The structure and mineralogy of coccoliths is very tightly controlled during the, intracellular, coccolith-formation process and so coccolith structure has proven a remarkably robust classification tool, well supported by modern molecular-genetic data. It also means biologists and palaeontologists use the same classification.

There are complications however, most obviously, typical coccolithophores have haplo-diplontic life-cycles with different coccoliths produced in haploid and diploid phases. The diploid phase heterococcoliths have complex structures formed of radial arrays of interlocking crystal units usually with alternating vertical and radial crystallographic orientations (V/R model). The different rim-structures of these heterococcoliths form the essential basis of the classification. The haploid phase holococcoliths are beautifully organised arrays of rhombohedral crystallites, but their morphology is relatively plastic and does not yield useful phylogenetic data. Finally, some other nannofossils occur which do not obviously fit either the heterococcolith or holococcolith model and these are conventionally refered to as nannoliths.

Understanding the classification of coccolithophores thus requires some basic knowledge of coccolithophore life-cycles, biomineralisation, crystallography and optical mineralogy (to interpret cross-polarised light images). A useful overview is provided by Bown & Young (1998) and other references which help explain the system applied here are listed below.

References:

Bown, P. R. & Young, J. R. (1998a). Introduction - calcareous nannoplankton biology. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 1-15. gs

Young, J. R., Didymus, J. M., Bown, P. R., Prins, B. & Mann, S. (1991a). Crystal assembly and phylogenetic evolution in heterococcoliths. Nature. 356: 516-518. gs

Young, J. R. et al. (1997). Guidelines for coccolith and calcareous nannofossil terminology. Palaeontology. 40: 875-912. gs V O

Young, J. R., Davis, S. A., Bown, P. R. & Mann, S. (1999). Coccolith ultrastructure and biomineralisation. Journal of Structural Biology. 126: 195-215. gs

Young, J. R., Geisen, M., Cros, L., Kleijne, A., Probert, I. & Ostergaard, J. B. (2003). A guide to extant coccolithophore taxonomy. Journal of Nannoplankton Research, Special Issue. 1: 1-132. gs V O

Young, J. R., Geisen, M. & Probert, I. (2005). A review of selected aspects of coccolithophore biology with implications for palaeobiodiversity estimation. Micropaleontology. 51(4): 267-288. gs

Daughter taxa: (blue => in age window 0-800Ma)		Granddaughter taxa
	Heterococcoliths
	Isochrysidales Heterococcoliths mostly placoliths with R-unit dominant. Motile phases with vestigial haptonema.	Noelaerhabdaceae Prinsiaceae Isochrysidaceae
	Coccolithales Mostly placolith heterococcoliths, with V-unit forming the distal shield; R-unit the proximal shield.	Coccolithaceae Calcidiscaceae Hymenomonadaceae Pleurochrysidaceae
	Zygodiscales Heterococcoliths with V-units forming upper/outer cycle of imbricated elements and R-units forming basal plate and central mass of irregular elements	Helicosphaeraceae Pontosphaeraceae Zygodiscaceae
	Syracosphaerales Coccoliths with radial lath cycle of T-units, and disjunct, often complex, axial structure, coccospheres often polymorphic	Calciosoleniaceae Rhabdosphaeraceae Syracosphaeraceae
	Coccolith families inc sed Various heterococcolith groups not obviously related to the well-defined orders	Alisphaeraceae Papposphaeraceae Umbellosphaeraceae narrow rimmed placoliths Coccolith genera inc sed unidentified
	Mesozoic Survivors Mesozoic taxa which occur in low abundances in the early Palaeogene.	Biscutaceae Chiastozygaceae Markalius Watznaueriaceae
	Holococcoliths & Nannoliths
	Holococcoliths Haploid life-cycle stages, with liths formed of numerous rhombohedral microcrystals	tubeless convex bridged flat-topped septate open-tube fossil holococcoliths U. extant holococcolith
	Braarudosphaerales Diploid (?) life-cycle stage covered by pentaliths (plates formed of 5 segments with lamellar sub-structure) formed extracellualrly	Braarudosphaeraceae
	Discoasterales Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.	Discoasteraceae Fasciculithaceae Heliolithaceae Sphenolithaceae
	Nannolith families inc sed Haptophytes forming calcareous structures not obviously homologous with heterococcoliths, holococcoliths, or discoasteralids	Ceratolithaceae Lapideacassaceae Lithostromationaceae Nannolith genera inc sed Rhomboasteraceae

Cenozoic and Modern Coccolithophores

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