Aktasia irregularis

Chiastozygus irregularis Cepek in Cepek & Hay, 1970

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

Large species of Aktasia (>6.0 µm) with a zeugoid outer wall and an eight-segmented protolith inner wall composed of large, sub-quadrilateral segments. The central area bears an asymmetrical diagonal cross lacking a distal process, with arms composed of parallel longitudinal segments, each divided into two halves.

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.