Citation: Calcidiscaceae Young & Bown, 1997taxonomic rank: FamilyTaxonomic 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).
Distinguishing features: Parent taxon (Coccolithales): 2N: Mostly placolith heterococcoliths with V-unit forming the distal shield; R-unit the proximal shield. Non-motile N: Form holococcoliths formed of single block, or non-calcifying This taxon: 2N: cells non-motile, bearing placoliths with R-unit confined to proximal shield, mostly circular. N: cells motile, holococcolith-bearing
Original description: Diagnosis: Coccosphaerales constans ex coccolithis cum R-unitis no nisi in proximo scuto.
Coccosphaerales consisting of coccoliths with R-units only in the proximal shield.
Description: Dominant phase of life-cycle, non-motile with placolith heterococcoliths. V-unit forms the distal shield and tube, extending to the proximal surface. R-unit forms the proximal shield. As in the Coccolithaceae, growth occurs downward from the proto-coccolith ring which becomes embedded within the structure so that alternating Vand R-units are only visible on specimens where the proximal shield has broken off. Distal shield sutures typically show laevogyral curvature. The proximal shield is usually monocyclic with radial sutures; sometimes it is bicyclic due to the development of a lower layer, with elements showing strong dextral obliquity (in proximal view). The connection between the proximal and distal shields is weak and they frequently separate.
Morphology: 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-cyclesDominant 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). However, although strains of Umbilicosphaera, and Oolithotus have been successfully cultured for long periods life-cycle transitions have not been obsrved in them (Probert pers. comm.), nor have combination coccospheres been recorded in field samples.
Search data:
Lith 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 ranges of the species in this database First occurrence (base): within NP4 zone (61.51-63.25Ma, base in Danian stage). Data source: Total of ranges of species in this database
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
Neptune data: this is a higher taxon page so Neptune data is not plotted. For the customisable plot option go to a genus page Parent: Coccolithales
References:
Geisen, M., Billard, C., Broerse, A. T. C., Cros, L., Probert, I. & Young, J. R. (2002a). Life-cycle associations involving pairs of holococcolithophorid species: intraspecific variation or cryptic speciation? European Journal of Phycology. 37: 531-550. gs
Houdan, A. et al. (2004a). Flow cytometric analysis of relative ploidy levels in holococcolithophore-heterococcolithophore (Haptophyta) life cycles. Systematics and Biodiversity. 1(4): 453-465. gs
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 Sciences, USA. 100(12): 7163-7168. 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. & Young, J. R. (eds) Coccolithophores - from molecular processes to global impact. Springer, Berlin 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., Henriksen, K. & Probert, I. (2004b). Structure and morphogenesis of the coccoliths of the CODENET species. In, Thierstein, H. R. & Young, J. R. (eds) Coccolithophores - From molecular processes to global impact. Springer, Berlin 191-216. gsO
Calcidiscaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-9-2024
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