Nannotax

Description: Elliptical placolith coccolith with central area open or spanned by a disjunct bar on the proximal surface.

Remarks: C. pelagicus is a very widespread, long ranging, and diverse species which could probably be usefully subdivided.

Range: Palaeocene to Recent

Extant sub-species

Two discrete morphotypes of C. pelagicus have been documented in the modern nannoflora e.g Cachao et al. 2000), culture studies and molecular gentics have shown that these are genotypically discrete but very closely related. They are variably distinguished as sub-species (Geisen et al. 2003, Young et al. 2003) or species (Saez et al. 2003).

• Coccolithus pelagicus (Wallich 1877) Schiller 1930 ssp. pelagicus Arctic form, liths 6-10 µm, central opening small and bar rudimentary, absent or becoming cross-like and filling opening. Occurs in waters <10°C. NB Wallich (1877) based his description of C. pelagicus on sediment samples from south of Iceland containing exclusively this morphotype. Holococcolih phase - planar with continuous cover of crystallites in rhombohedral array (formerly called Crystallolithus hyalinus Gaarder & Markali 1957).

  Coccolithus pelagicus ssp. braarudii (Gaarder 1962) Geisen et al. 2002 Temperate form, liths 9-15 µm, central opening wide, usually spanned by well-formed bar that extends to the edge of the central area. Occurs in waters ca. 14-18°C. Holococcolith phase - planar with incomplete cover of crystallites arranged in radial strings extending from a central ellipse (formerly called Crystallolithus braarudii Gaarder 1962).

Palaeontological variation

Coccolithus is highly variable in the Neogene although only C. miopelagicus is regularly regarded as a discrete species. Note in particular that:

1. Forms with well-developed bridges only occur in the Late Pliocene and Quaternary

2. C. pelagicus largely disappears from low latitude waters in the Early Pleistocene.