Contributions Series Nr. 9

Description

Abstract

The taxonomy of a stratigraphically important group of Upper Mesozoic dinoflagellate cyst genera, centred about the genus Gonyaulacysta Deflandre, is re-examined. The morphology of its type species, G. jurassica (Deflandre), is shown to be more variable than hitherto recognized, embracing cornucavate to bicavate forms exhibiting great variation in the form of cavation, crests, horn development, the presence or absence of gonal spinules and of posterior extensions of the crests (here termed “caudiculae”) and the development of claustra. The morphology of three other species – Gonyaulacysta eisenackii (Deflandre), Psaligonyaulax dangeardii (Sarjeant) and Rhynchodiniopsis aptiana Deflandre is also considered in detail: the latter is shown to be characteristically cornucavate. Problems in the interpretation of related genera are discussed.

As a result of this analysis, revised diagnoses are presented for the Family Gonyaulacystaceae and for the genera Acanthaulax, Cribroperidinium, Gonyaulacysta, Hystrichosphaeropsis, Leptodinium, Millioudodinium, Rhynchodiniopsis and Tubotuberella, the specific content of each being examined and 34 taxonomic transfers of species being proposed. One new species, Gonyaulacysta vozzhennikovae, two new subspecies, Gonyaulacysta jurassica adecta and Tubotuberella dangeardii primitiva, and one new variety, G. jurassica jurassica var. longicornuta, are described. Emended diagnoses are presented for the following taxa – Gonyaulacysta jurassica (Deflandre ), its subspecies jurassica and its variety longicornis, Gonyaulacysta eisenackii (Deflandre), Rhynchodiniopsis aptiana Deflandre, Tubotuberella apatela (Cookson and Eisenack), T. dangeardii (Sarjeant) and T. egemenii (Gitmez). Reasons are presented for treating as junior synonyms the genera Dimidiadinium Brideaux and Glabridinium Brideaux, the species Tubotuberella sphaerocephalus Vozzhennikova and Psaligonyaulax dualis Brideaux and Fisher, and the subspecies Gonyaulacysta jurassica brevis Johnson and Hills.