Watznaueria angustoralis Reinhardt, 1964
Colvillea Black 1964
Caterella Black, 1971
Calolithus Noël, 1965
Maslovella Tappan & Loeblich 1966
Margolatus Forchheimer, 1972
Actinosphaera Noël,1965
Subcircular to elliptical placoliths composed of single-tiered distal and proximal shields, a double tube cycle, a locking cycle, and a central area that may be open or closed but lacks bar or cross structures. The locking cycle lies between the tube cycles and the shields and is expressed on the proximal side of the placolith. The two tube cycles are distinguishable under phase-contrast or bright-field illumination owing to subtle differences in their relative heights.
In plan view under cross-polarised light, the shields and tube cycles exhibit interference colours, inclined extinction lines, and length-fast (–) elongation. The locking cycle may also display interference colours, but more commonly remains in constant extinction.
The presence of two tube cycles may be inferred from differences in the orientation of the extinction lines within the placolith, together with observations under phase-contrast or bright-field illumination.
Among the species examined, Watznaueria diaphanae is unique in exhibiting parallel extinction, a character that readily distinguishes it from the others.
Watznaueria differs from Ellipsagelosphaera in possessing a featureless or closed central area, whereas the latter exhibits a disjunct transverse bar. Watznaueria is further distinguished from Cyclagelosphaera by its typically elliptical outline and from Lotharingius by the absence of cross structures in the central area.
The species considered in this study can be informally divided into two groups based on the optical properties of the locking cycle. In one group, the locking cycle displays interference colours, obscuring the boundary between the shield and tube cycles. In the other, the locking cycle remains in constant extinction, forming a narrow dim cycle between the shield and tube cycle that clearly delineates the two structures.
Species in which the locking cycle is expressed as a narrow dim suture, clearly separating the shield from the tube cycle, include taxa with a closed central area (Watznaueria angustoralis, Watznaueria deflandrei, and Watznaueria paenepelagica) and taxa with an open central area (Watznaueria coronata, Watznaueria fossacincta, Watznaueria martelae, and Watznaueria tubulata).
Species in which the locking cycle displays interference colours, producing a transitional boundary between the tube cycle and shield, include taxa with a closed central area (Watznaueria arata, Watznaueria cauveryensis, Watznaueria cf. cauveryensis, Watznaueria prionocycla and Watznaueria leesiae) and taxa characterised by two central pores (Watznaueria biporta and Watznaueria cynthae).
Species with an indistinct tube cycle–shield boundary comprise small elliptical forms (4.0–7.0 µm), including Watznaueria bayackii, and Watznaueria diaphanae. The most notable feature within this group is the parallel extinction observed in Watznaueria diaphanae, whereas all other Watznaueria species exhibit inclined extinction in the shields.
Black, M. 1964. Cretaceous and Tertiary coccoliths from Atlantic seamounts. Palaeontology 7: 306-316.
Black, M. 1971a. Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society 38: 381-424.
Black, M. 1973. British Lower Cretaceous Coccoliths. I-Gault Clay (Part 2). Palaeontographical Society Monograph 127: 49-112.
Forchheimer, S. 1972. Scanning electron microscope studies of Cretaceous coccoliths from the Köpingsberg Borehole No. 1, SE Sweden. Sveriges Geologiska Undersökning, Series C. #668, 65: 1-141.
Loeblich, A. R. & Tappan, H. 1966. Annotated index and bibliography of the calcareous nannoplankton. Phycologia. 5: 81-216.
Noël, D. 1965. Sur les Coccolithes du Jurassique Européen et d'Afrique du Nord. Essai de classification des coccolithes fossiles. Éditions du Centre National de la Recherche Scientifique, Paris. 1-129.
Reinhardt, P. 1964. Einige Kalkflagellaten-Gattungen (Coccolithophoriden, Coccolithineen) aus dem Mesozoikum Deutschlands. - Monatsberichteder Deutschen Akademieder Wissenschaftenzu Berlin. 6: 749-759.