Arkhangelskiella striata Stradner, 1963
The placolith comprises a cretarhabdid pelaga sloping towards the central area, formed of inclined segments that are typically weakly clockwise-imbricated, though rarely non-imbricate, and a distally arched central area characterised by a fibrous axial cross supporting a solid distal process. Each quadrant bears four or more lateral bars. The spaces between the lateral bars are occupied by multiple pores aligned along the bars and in longitudinal rows across successive bars.
In Cretarhabdus, the pores are arranged in concentric rings.
The placolith generally displays first-order, greyish-white interference colours; however, it becomes dimmer towards the periphery, where only the inner layer of the distal shield is developed. In plan view under crossed polars, the outer layer of the distal shield exhibits inclined extinction and length-fast (–) elongation.
Grün, W. & Allemann, F. 1975. The Lower Cretaceous of Caravaca (Spain): Berriasian Calcareous Nannoplankton of the Miravetes Section (Subbetic Zone, Prov. of Murcia). Eclogae Geologicae Helvetiae, 68: 147-211.
Stradner, H. 1963. New contributions to Mesozoic stratigraphy by means of nannofossils. Proceedings of the Sixth World Petroleum Congress. Section 1 Paper 4: 167-183.