Nannotax Enabling nannofossil research

Description: Symmetric 5-rayed discoaster (with rare 3 and 4 rayed variants); ray tips with acute bifurcations. Strongly concavo-convex and birefringent (each ray is a separate crystal-unit, with c-axes inclined slightly from vertical toward radial). The central area is small, but distinct. It often has scalloped depressions and/or sutural ridges on the distal side, also a stellate proximal knob

Remarks: D. pentaradiatus is very distinctive; both the acutely angled bifurcations and the birefringence, with each ray showing slightly different optical orientation are uniquely diagnostic of the species. With dissolution the bifurcations can be removed and such forms have been described as separate species (see synonyms below), however the birefringence allows definitive identification of such specimens.

Range: NN10B to NN17. Often very abundant, but highly susceptible to dissolution.

Species name: Theodoridis (1984), argued that use of the name D. pentaradiatus for this species was based on a misconception of Tan's type specimen, and of Bramlette & Riedel's emended diagnosis. He proposed the alternative name E. misconceptus. This interpretation has not however been followed, and if an alternative name to D. pentaradiatus was used D. tridenus has priority over D. misconceptus.

Synonyms:

• Discoaster anconitanus Borsetti and Cati, 1972 - etched form, lacking bifurcations
• Discoaster misconceptus (Theodoridis, 1984) Muza and Wise, in Muza et al., 1987 [Eudiscoaster] - alternative name proposed for nomenclatural reasons (see notes on species name).
• Discoaster stradneri Cati & Borsetti 1970 - etched form, lacking bifurcations
• Discoaster tridenus Kamptner, 1967 etched form, lacking bifurcations.
• Discoaster ono Styzen, 1994 - very short non-bifurcate rays, probably a preservational artefact