This study presents the results of a five-year research on Lower Cretaceous dinoflagellate cysts (dinocysts). The new concepts and observations described herein are supported by the study of hundreds of samples coming from various palaeogeographical domains: boreal, tethysian or austral. The framework of the study is based on a fine morphological study of thousands of specimens. This research brings forward the various interactions between morphology, systematics, biostratigraphy and palaeoecology.

Morphology and systematics. The choice of a better descriptive vocabulary and of proper morphological criteria, the latter chosen as much as possible for their alternative (yes or no) character, allows to define a better adapted terminology (e.g. in the genera Odontochitina DEFLANDRE 1935 and Xenascus COOKSON & EISENACK 1969). This new terminology leads to more systematical, less litterary and non ambiguous diagnoses, which bring back to the concept of "species" its true universal value (e.g. in the genus Muderongia COOKSON & EISENACK 1958). This new terminology results in numerous taxonomic changes: emendations, new combinations or creation of new genera and species (e.g. revision of the genus Cometodinium DEFLANDRE & COURTEVILLE 1939 and creation of the new species C. habibi). The value of a critical synonymy is emphasized. Finally, determination keys accessible to non-specialists are established: they include the new terminology and taxonomic data, and use schematic symbols which permit a quick visualization of the determination criteria (e.g. in the genera Amphorula DODEKOVA 1969 and Palaeotetradinium DEFLANDRE 1936).