The Cenozoic gonyaulacacean dinoflagellate genera Operculodinium Wall, 1967 and Protoceratium Bergh, 1881 and their phylogenetic relationships

Abstract

To clarify the systematic positions of the important gonyaulacacean genera Operculodinium Wall, 1967 emend. Matsuoka et al., 1997 and Protoceratium Bergh, 1881, we present in detail the tabulation of the Oligocene–Pleistocene, thermophilic, cyst-defined species Operculodinium bahamense Head in Head and Westphal, 1999 emend., and the extant, cosmopolitan, theca-defined species Protoceratium reticulatum (Claparède and Lachmann, 1859) Bütschli, 1885. Both species have a sexiform hyposomal tabulation, and L-type (Protoceratium reticulatum) or modified L-type (Operculodinium bahamense) ventral organization. Protoceratium reticulatum has dextral torsion of the hypotheca, requiring assignation of the genus to the subfamily Cribroperidinioideae Fensome et al., 1993, whereas Operculodinium bahamense has neutral torsion requiring assignation to the subfamily Leptodinioideae Fensome et al., 1993. The stratigraphic range of this subfamily is now extended upwards to the lower Pleistocene. Paradoxically, Protoceratium reticulatum produces a cyst whose morphology is circumscribed by the cyst-defined genus Operculodinium, either implying polyphyletic origins for this genus or that combinations of ventral organization and torsion used to subdivide the family Gonyaulacaceae cannot always be applied rigidly. In detail, Operculodinium bahamense is shown to have an unusual ventral tabulation in which the first apical plate contacts the apical pore complex but not the sulcus. The new term “episert” is proposed to describe this plate relationship, which appears to have evolved independently in several lineages of the suborder Gonyaulacineae.

Differences in the chemical composition of organic‐walled dinoflagellate resting cysts from phototrophic and heterotrophic dinoflagellates

“… Sample numbers correspond to Table ; a Rochon et al. (); b Paez‐Reyes and Head (); previously Operculodinium centrocarpum sensu Wall and Dale; c Matsuoka et al. (); d This study; e Matsuoka (); f McCarthy et al.…”

Ceratocorys mariaovidiorum sp. nov. (Gonyaulacales), a new dinoflagellate species previously reported as Protoceratium reticulatum

“…The plate tabulation of Ceratocorys mariaovidiorum was based herein on plate homologies of other gonyaulacoid genera (Fensome et al. , Paez‐Reyes and Head ), giving a thecal plate formula Po, 4′, 0a, 5″, 6c, ~7s, 5‴, 0p, 2′′′′. However, a different interpretation of the 3′ plate can be made when it is not in contact with Po (1a according to the Kofoid system), resulting in a plate formula Po, 3′, 1a, 5″, 6c, ~7s, 5‴, 0p, 2′′′′.…”

“…In this article, a relaxed Kofoid nomenclature system that recognizes homologies of plates of other gonyaulacoid genera was used (Fensome et al. , Paez‐Reyes and Head ). The plate, which, following the Kofoid system, should be named an anterior intercalary plate (1a), was considered here as the homologue of the third apical plate of other gonyaulacoids because it can contact the apical pore plate (Po), and hence is named 3′ (Table ).…”

Mid‐Piacenzian Variability of Nordic Seas Surface Circulation Linked to Terrestrial Climatic Change in Norway

“…At least 300 dinocysts were identified for each sample, and Table provides a taxonomic list of species encountered in the Piacenzian sediments of ODP Hole 642B. Cysts of Protoceratium reticulatum (also known as Operculodinium centrocarpum sensu Wall & Dale, ; see Paez‐Reyes & Head, ) with processes smaller than 2 μm (cf. Rochon et al, ) were counted separately in 34 samples (the morphotype was not differentiated in the remaining 10 samples).…”