Nannotax Enabling nannofossil research

Description: Coccoliths circular to sub-circular. Proximal shield, birefringent, distal shield non-birefringent with curved sutures. Shields easily separated.

Remarks: 

Type species: C. quadriforatus (subj. j. syn. of C. leptoporus).

Synonyms:

• Cyclococcolithina Wilcoxon, 1970;
• Cyclococcolithus Kamptner, 1954;
• Cycloplacolithus Kamptner, 1963.

Variant:

• Cycloperfolithus Lehotayova and Priewalder, 1978 - with fine grill in central-area, and bicyclic proximal shield.

Species-level taxonomy:

Calcidiscus is common throughout the Neogene
and shows significant variaton in size, number of elements, opening of
central area, and structural details. Species concepts have been extensively discussed,
most notably by Knppertsbusch (2000). Recent research has lead to
a three-fold divsion of the extant Calcidiscus population, see e.g. Quinn et al. (2004), Young et al. (2003):

• C. quadriperforatus; large, 7-10µm, with zone of obscured sutures around the central area. Haploid phase produces septate holococcoliths (formerly classified as Syracolithus quadriperforatus)
• C. leptoporus - intermediate; 5-8µm, with continuous sutures. Haploid phase produces planar holococcoliths (formerly classified as Crystallolithus rigidus)
• C. leptoporus - small; 3-5µm, with kinked sutures. Haploid phase not known.

By comparison Pliocene Calcidiscus assemblages are usually classified into:

• C. leptoporus; 3-8µm circular to sub-circular with closed central area
• C. tropicus & C .macintyrei; 5-11µm circular with open central area.

It is not sure how these species relate to the extant species but the
degree of variation shown in fossil assemblages suggests that many more
speces could probably be recognised.