Aktasia irregularis

Chiastozygus irregularis Cepek in Cepek & Hay, 1970

Helicolithus compactus (Bukry, 1969) Varol & Girgis, 1994

Large species of Aktasia (< 6.0 µm) have a zeugoid outer wall and a protolith inner wall composed of eight large sub-quadrilateral segments. The central area contains an asymmetrical diagonal cross whose arms are composed of parallel longitudinal segments arranged in two halves and lacking a distal process.

Aktasia irregularis is identified from Aktasia compacta by being greater than 6.0 µm.

Aktasia irregularis differs from Aktasia disgregatus by having an asymmetrical cross, whereas the latter has a symmetrical cross.

Bukry, D. 1969. Upper Cretaceous coccoliths from Texas and Europe. University of Kansas Paleontological Contributions, Articles 51 (Protista 2): 1-79.

Cepek, P. & Hay, W.W. 1970. Zonation of the Upper Cretaceous using calcareous Nannoplankton. Palaont. Abh. Abt. B Palaobotanik. 3(3/4): 333-340.

Stover, L. E. 1966. Cretaceous coccoliths and associated nannofossils from France and the Netherlands. Micropaleontology 12(2): 133-167.

Varol, O. & Girgis, M. 1994. New taxa and taxonomy of some Jurassic to Cretaceous calcareous nannofossils. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 192: 221-253.