Discoaster

Archontikis, Odysseas A., Millán, Josué G., Winter, Amos & Young, Jeremy R., 2023, Taxonomic re-evaluation of Ericiolus and Mercedesia (Prymnesiophyceae) and description of three new species, Phycologia 62 (2), pp. 179-193 : 191

DISCOASTER

Discoaster is an important genus of nannofossils that were abundant through most of the Cenozoic, especially in warm oligotrophic waters. The last two species, D. brouweri S.H. Tan and D. triradiatus S.H. Tan went extinct 1.8 million years ago, in the Early Quaternary. Like Ericiolus , Discoaster nannoliths have radial symmetry, being formed of rays that grow from a central axis, rather than a proto-coccolith ring as in heterococcoliths ( Young et al. 1999). This radial growth pattern, however, is characteristic of not only Discoaster but several other major extinct Cenozoic nannofossil groups, notably Fasciculithus Bramlette & F.R. Sullivan , Heliolithus Bramlette & F.R. Sullivan and Sphenolithus Deflandre , which are now grouped together as the Discoasterales W.W. Hay emend. Bown ( Bown 2010) . Moreover, the last Discoaster species show three- or six-fold symmetry and have deflected ray tips. Of the eight species of Ericiolus , Ericiolus bendifii sp. nov., is, in particular, remarkably reminiscent of a miniature D. brouweri or D. surculus E. Martini & Bramlette. Meier et al. (2014) noted that the crystallographic origin of the elements in Pileolosphaera was the same as that in Discoaster , with the c-axes vertical/ parallel to the axis of rotational symmetry of the nannolith. Unfortunately, Ericiolus is too small to determine crystallographic orientation optically and we do not have suitable samples for X-ray diffraction studies. Nonetheless, this type of analyses would be an interesting test, as would molecular genetics, to confirm whether Ericiolus is instead related to another group of extant coccolithophores.