Classification: Coccolithophores -> Isochrysidales
Sister taxa: Isochrysidales, Coccolithales, Zygodiscales, Syracosphaerales, Coccolith families inc sed, Mesozoic Survivors, Holococcoliths, Braarudosphaerales, Discoasterales, Nannolith families inc sed, hidden,

Distinguishing features: Heterococcoliths mostly placoliths with R-unit dominant. Motile phases with vestigial haptonema.

Daughter taxa: (blue => in age window 0-800Ma) Granddaughter taxa
Heterococcoliths with Reticulofenestra-type structure, V-units vestigal, R-units forming grill, both shields, and two-layered tube

Placoliths with R-units forming the lower layer of proximal shield, inner tube and middle tube; V-units forming an upper layer to the proximal shield, outermost tube and the distal shield. In LM they display a dark outer cycle and brighter inner cycle. Central-area structures are conjunct, formed from the R-units.

Non-calcifying Isochrysidales


Citation: Isochrysidales Pascher, 1910
Rank: Order
Notes & discussion: Grouping of the Prinsiaceae and Noelaerhabdaceae is based on coccolith structure and stratophenetic data (Young et al. 1992; Young & Bown 1997). Grouping of the Isochrysidaceae and Noelaerhabdaceae is based on flagellar characters (haptonema vestigial), this was questioned by (Green & Jordan 1994) but has been strongly supported by biochemical characters (production of alkenones) and molecular genetics (Edvardsen et al. 2000; Fujiwara et al. 2001; Sáez et al. 2004). The order Isochrysidales Pascher 1910 is used for these three families instead of Prinsiales Young & Bown, 1997, since it has priority.

Farinacci & Howe catalog pages: Isochrysidales [no catalog entry yet]

Distinguishing features: Heterococcoliths mostly placoliths with R-unit dominant. Motile phases with vestigial haptonema.

Morphology remarks: Coccoliths are placoliths, but unlike the Coccolithaceae, growth does not occur downward from the proto-coccolith ring. The R-unit is always well developed, forming a proximal shield element, two tube-elements with opposite senses of imbrication, and usually a central-area element. The locus of the proto-coccolith ring is usually marked by a ring of slits on the proximal surface. Central-area structures are always conjunct, being formed from either the central-area element or the inner tube-element of the proximal shield. In the Prinsiaceae, the V-unit is well developed (Toweius-type structure); forming an upper layer to the proximal shield, an outermost tube and the distal shield. In the Noelaerhabdaceae, the V-unit is virtually absent (Reticulofenestra-type structure) and the outer of the two R-unit tube-cycles is extended to form the distal shield.
References: Young et al. 1992; Young et al. 2004 codenet species;

Search data:
MetricsLith size: 0->0µm;
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): Extant Data source: Total of range of species in this database
First occurrence (base): at base of Danian Stage (0% up, 66Ma, in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:


Edvardsen, B.; Eikrem, W.; Green, J.C.; Andersen, R.A.; Moon-Van Der Staay, S.Y. & Medlin, L.K., (2000). Phylogenetic reconstructions of the Haptophyta inferred from 18S ribosomal DNA sequences and available morphological data. Phycologia, 39: 19-35.GS

Fujiwara, S.; Tsuzuki, M.; Kawachi, M.; Minaka, N. & Inouye, I., (2001). Molecular phylogeny of the haptophyta based on the rbcL gene and sequence variation in the spacer region of the RUBISCO operon. Journal of Phycology, 37: 121-129.GS

Green, J.C. & Jordan, R.W., (1994). Systematic history and taxonomy. In: Green, J.C. and Leadbeater, B.S.C. (Editors), The Haptophyte Algae. Systematics Association Special Volumes. Clarendon Press, Oxford, pp. 1-21.GS

Pascher, A., (1910). Chrysomonaden aus dem Hirschberger Grossteiche. Monographien und Abhandlungen zur Internationalen Revue der gesamten Hydrobiologie und Hydrographie, 1: 66.GS

Perch-Nielsen, K., (1985). Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.B. and Perch-Nielsen, K. (Editors), Plankton Stratigraphy. Cambridge University Press, Cambridge, pp. 427-555.GS

Sáez, A.G.; Probert, I.; Young, J.R.; Edvardsen, B.; Wenche, E. & Medlin, L.K., (2004). A review of the phylogeny of the Haptophyta. In: Thierstein, H.R. and Young, J.R. (Editors), Coccolithophores - from molecular processes to global impact. Springer, pp. 251-270.GS

Young, J.R. & Bown, P.R., (1997). Cenozoic calcareous nannoplankton classification. Journal of Nannoplankton Research, 19(1): 36-47.GS

Young, J.R.; Didymus, J.M.; Bown, P.R.; Prins, B. & Mann, S., (1992). Crystal assembly and phylogenetic evolution in heterococcoliths. Nature, 356: 516-518.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


Isochrysidales compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 25-4-2019

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