Observations and Recommendations on the Fossil Dinocyst Genera Ctenidodinium, Dichadogonyaulax, and Korystocysta

Abstract

The fossil dinocyst genus Dichadogonyaulax, erected by Sargeant in 1966, has proven to be very controversial. It has been synonymized with Ctenidodinium at least twice and resurrected at least twice. The separation of the two genera was based on the equal development of paracingular ornamentation in Dichadogonyaulax and the unequal development of those features in Ctenidodinium. This paracingular differentiation is a somewhat variable feature and probably not of generic significance.

There is, however, a fundamental difference in the paratabulation of the epicyst between representatives of the two genera. The type species of Ctenidodinium, C. ornatum, exhibits a preapical paraplate separating the second and fourth apical pa1·aplates and also possesses anterior intercalary paraplate(s); whereas the type of Dichadogonyaulax, D. culmula, either has no preapical para plate or it is reduced and displaced toward the ventral surface, thus allowing contact between the second and fourth apical paraplates. No anterior intercalary paraplates are present in D. cuimula.

Korystocysta, erected by Woollam in 1983, has a Ctenidodinium style epicystal paratabulation and differs from Ctenidodinium in having an abbreviated apical horn and accessory parasutural ("growth bands'') ridges.