Perchnielsenaceae

This family is characterised by tubular calcareous nannofossils with a double-storey, unicyclic wall structure. Each storey consists of numerous segments strongly imbricated in a sinistral orientation. The two walls often differ in height, and at their intersection, a disjunct amedian diaphragm extends. The outer surface is commonly ornamented with both lateral and longitudinal features.

Optical Properties: Perchnielsenaceae exhibit parallel (straight) extinction with length-fast (-) elongation in the plan view and length-slow (+) elongation in the side view. First-order yellow to second-order blue interference colours are observed, reflecting the significant height and width (retardation colours).

The species in this family can settle randomly in either plan or side view due to its similar height-to-width ratio.

Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222