Classification: Coccolithophores -> Coccolithales -> Calcidiscaceae
Sister taxa: Coccolithaceae, Calcidiscaceae, Hymenomonadaceae, Pleurochrysidaceae,

Distinguishing features: Liths with R-unit confined to proximal shield, mostly circular

Daughter taxa: (blue => in age window 0-300Ma) Granddaughter taxa
Circular or sub-circular; central area closed or with narrow opening

Coccoliths polygonal, thin; proximal shield much smaller than distal

Coccoliths asymmetric, tube and proximal shield offset from centre of distal shield

Central area open

Coccoliths elliptical, grill in central area

Coccoliths cylindrical, with shields separated by an elevated tube


Citation: Calcidiscaceae Young & Bown, 1997
Rank: Family
Notes & discussion: Genera included:
NB All these genera were included within the Coccolithaceae in older classifications but were separated by Young & Bown (1987) into the family Calcidscaceae on the grounds of them sharing a simpler coccolith structure than that of the Coccolithaceae. The grouping has been supported by molecular genetic data (Sáez et al., 2003, 2004).

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

Distinguishing features: Liths with R-unit confined to proximal shield, mostly circular

Morphology remarks: Coccoliths are placoliths with rim structure similar to Calcidiscus, i.e. the V-unit forms distal shield and central-area/tube; R-unit forms proximal shield only. As in the Coccolithaceae, growth occurs downward from the proto-coccolith ring which becomes embedded within the structure so that alternating V- and R-units are only visible on specimens where the proximal shield has broken off (Young et al. 2004).
Distal shield sutures usually show laevogyral curvature. The proximal shield is usually formed of a single layer of elements with sub-radial sutures; sometimes a lower layer is developed, with elements showing strong dextral obliquity (in proximal view). The connection between the proximal and distal shields is weak and they frequently separate.

Biology & life-cycles: Dominant phase of life-cycle non-motile with placolith heterococcoliths. Holococcolith bearing motile phase has been documented in the extant species C. leptoporus and C. quadriperforatus (refs. Geisen et al. 2002, Houdan et al. 2004).

Search data:
TagsLITHS: placolith, circular, elliptical,
CSPH: spherical, monomorphic, V-UNITS: distal shield, tube, R-UNITS: prox shield, DETAILS: isogyres oblique, rim-unicyclic,
MetricsLith size: 2.5->15µm;
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): in upper part of Danian Stage (63% up, 63.2Ma, in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:


Geisen, M.; Billard, C.; Broerse, A.T.C.; Cros, L.; Probert, I. & Young, J.R., (2002). Life-cycle associations involving pairs of holococcolithophorid species: intraspecific variation or cryptic speciation? European Journal of Phycology, 37: 531-550.

Houdan, A.; Billard, C.; Marie, D.; Not, F.; Sáez, A.G.; Young, J.R. & Probert, I., (2004). Flow cytometric analysis of relative ploidy levels in holococcolithophore-heterococcolithophore (Haptophyta) life cycles. Systematics and Biodiversity, 1(4): 453-465.

Sáez, A.G.; Probert, I.; Geisen, M.; Quinn, P.; Young, J.R. & Medlin, L.K., (2003). Pseudo-cryptic speciation in coccolithophores. Proceedings of the National Academy of Science of the United States of America, 100(12): 7163-7168.

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.

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

Young, J.R.; Henriksen, K. & Probert, I., (2004). Structure and morphogenesis of the coccoliths of the CODENET species. In: Thierstein, H.R. and Young, J.R. (Editors), Coccolithophores - From molecular processes to global impact. Springer, pp. 191-216.


Calcidiscaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-12-2018

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