P. sagittifera HOL (Figs 23–26)

A selection of complete cells from West Greenland and the North East Water Polynya (Figs 23–26) are illustrated to show the general appearance of the cell with flagella and haptonema. Symmetrical tower-shaped holococcoliths, flaring at both ends (apple-core shaped), radiate from the entire cell surface. A monolayer of hexagonal plates of crystallites covers the entire surface of the holococcolith often united to form larger scale patterns (e.g. Fig. 26). The similarity between cells illustrated here and those included as part of the type description (Manton et al. 1976b) is fairly convincing, also when it comes to dimensions there is an overall agreement.

The coccosphere diameter is in our material ca. 12 µm, and the diameter of the cell ca. 6 µm. The tower-shaped holococcoliths vary in length from roughly 1.5 to 3.5 µm. The minimum width along the tower is 0.4–0.6 µm. Manton et al. (1976a) found that the plates of crystallites in the type material measured 0.15 µm across. When measuring 64 randomly selected individual plates from Fig. 26 (mean value: 0.144 ± 0.018 µm / overall range: 0.09–0.17 µm) the result thus corroborates the observation by Manton et al. (1976b).