Helicosphaera kilida

Helicosphaera kilida Varol, 2025

A helicolith characterised by a Type III (Helicosphaera carteri type) blanket, an expanded flange termination, and a central area occupied by a multi-segmented disjunct inverse plate/bar that fills the central opening entirely.

Derived from the Greek kilida, meaning “patch,” referring to the disjunct central plate composed of several minute, irregular segments resembling patchwork.

Optical Properties: Helicosphaera kilida exhibits inclined extinction angles of about 65° on the blanket on the distal side and shows length-fast (−) elongation.

Helicosphaera kilida differs from Helicosphaera intermedia by the presence of this multi-segmented disjunct inverse plate/bar. In contrast, Helicosphaera intermedia features a well-defined oblique disjunct bar that often leaves an open space of varying width.

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