Discoaster

Discoaster brouweri Tan Sin Hok, 1927

Eu-discoaster Tan Sin Hok, 1927

Helio-discoaster Tan Sin Hok, 1927

Hemi-discoaster, Tan Sin Hok, 1927

Asterolithes Sujowski, 1931

Gyrodiscoaster Stradner, 1961

Agalmatoaster (Gemminiodicoaster) Prins, 1971

Radiodiscoaster (Curvidiscoaster) Prins, 1971

Truncodiscoaster Prins, 1971

Turbodiscoaster Prins, 1971

- Stellate, rosette shape or discoidal nannolith, often concave-convex.

- The segments are non-birefringent in plan view.

- The inner end of the segments may form distal and proximal processes.

- The segments entirely or partly join each other.

- The termination of segments can be simple, bifurcated or twisted.

- The ridges, depressions, or other ornamentations may be present on the segments.

- The two major groups can be identified [each group can be further subdivided]:

- Rosette-shaped discoasters have segments joined to each other almost entirely along their length.

- Stellate discoasters, having segments only partly joined to each other, leaving a distinct free length of segments.

Herendeen (2016) confirmed that the International Code of Nomenclature (ICN) had approved the proposal by Dowel (2014) to conserve the name Discoaster. This decision ensures the continued use and recognition of the name Discoaster in scientific literature and research, maintaining consistency and clarity in the classification and study of these essential nannofossils.

The optical properties of Discoaster, including constant extinction (dim) in the plan view and interference colours due to birefringence in the side view under XPL, align with those observed in the family Discoasteraceae.

The species of Discoaster are identified based on the following main criteria:

• The number of segments, the length of each segment, how the segments terminate, and whether nodes are present or absent.
• The diameter of the central area and its ornamentation.- The ratio of the central area to the free length of the segments.
• The shape of the areas between segments.

Prins, B. 1971. Speculations on relations, evolution and stratigraphic distribution of discoasters. In: Farinacci, A. (Ed.) - Proceedings of the Second Planktonic Conference Roma 1970. Edizioni Tecnoscienza, Rome 2: 1017-1037.

Stradner, H. 1961. Vorkommen von Nannofossilien im Mesozoikum und Alttertiär. Erdoel-Zeitschrift 77(3): 77-88.

Sujkowski, Z. 1931. Étude pétrographique de Crétacé de Pologne. Sprawozdania Polskiego instytutu geologicznego. 6: 485-628.

Tan Sin Hok. 1927a. Discoasteridae incertae sedis. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Sect Sci, 30: 411-419.