Watznaueria fossacincta

Ellipsagelosphaera fossacincta Black, 1971a

The shields, as well as the tube cycles, display first-order white interference colours with inclined extinction lines and length-fast (–) elongation. In distal view, the extinction angles in the distal shield are approximately 67°. This angle cannot be directly measured in the tube cycles due to the oblique orientation of their constituent segments; however, the apparent angle between extinction lines in the tube cycle is about 62°, corresponding to an obliquity of about 28°. Differentiation of the inner and outer tube cycles is difficult under all illumination conditions.

Elliptical species of Watznaueria characterised by a relatively small subcircular to elliptical central opening devoid of internal structures. The width of the central opening is consistently less than 1.0 µm. Watznaueria fossacincta differs from Watznaueria coronata in possessing a small subcircular to elliptical central opening, whereas the latter exhibits a narrow, elongate opening.

Watznaueria fossacincta is further distinguished from Watznaueria martelae by its smaller central opening (<1.0 µm), whereas the latter has a larger opening (>1.0 µm). In addition, extinction angles in the tube cycles and shields differ significantly between the two species.

Black, M. 1971a. Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society 38: 381-424.

Bown, P. R. & Cooper, M. K. E. 1989b: New calcareous nannofossils from the Jurassic. Journal of Micropalaeontology 8: 91-96.