A morphological comparison of two cladopyxidacean dinoflagellates: the extant Micracanthodinium setiferum and the fossil Cladopyxidium saeptum (Dinophyceae, Gonyaulacales)

Abstract

Among dinoflagellates, extant cladopyxidaceans may provide a missing link to better understand the first evolutionary transformations from ancestral configurations toward the more abundant and more derived patterns in Gonyaulacales and Peridiniales. A restudy of the extant, motile-defined Micracanthodinium setiferum using plankton samples from the Indian and Atlantic oceans and the Mediterranean Sea demonstrates that the correct plate formula is Po, Pt, X, 3′ + *4′, 4a, 7′′, 7C, 4S, ?6′′′, 0p, 2′′′′. A ventral pore is found between 1′, 3′ and *4′. A restudy of the extinct, fossil-defined Cladopyxidium saeptum from the upper Paleocene of Delaware (USA), demonstrated the presence of an identical tabulation. A ventral pore (= porichnion) was positioned between *1′ and 7′′. Cladopyxidium is morphologically closer to Micracanthodinium than to Cladopyxis. Since Cladopyxidium has been extinct since the middle Eocene, it is unlikely that Micracanthodinium and Cladopyxidium have a direct biological link; the close morphological similarity between them does, however, suggest an important phylogenetic relationship between them in the evolution of cladopyxidaceans.

Keywords:

• dinoflagellates
• partiform
• Kofoidian
• porichnion
• Paleocene
• Eocene

Acknowledgements

The Regional Council of Brittany, the General Council of Finistère, and the urban community of Concarneau-Cornouaille-Agglomération are acknowledged for funding the Sigma 300 FE-SEM of the station of Marine Biology in Concarneau. MCC-M thanks Prof. Balech for the Equalant I sample which he kindly sent her many years ago for studies on podolampadaceans. The samples from the Coral Sea were kindly supplied by Prof. Gustaaf Hallegraeff, also many years ago, for the same purpose. MCC-M also thanks Bethan Jones and Brian Verwey for taking the samples during the NAAMES 1 and NAAMES 3 campaigns, respectively. Marta Torres (Oregon State University) is thanked for sampling in the Mediterranean Sea for MCC-M. Lucy Edwards is greatly acknowledged for interesting discussions and providing samples. Two anonymous reviewers and the editor are thanked for constructive remarks that improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

MCC-M thanks the Oregon State University Research Incentive Program for funding scanning electron microscopy. NAAMES was supported by a NASA Grant [grant number NNX15AF30G] to Dr. Michael J. Behrenfeld.

Notes on contributors

Kenneth Neil Mertens

KENNETH NEIL MERTENS is a researcher at Ifremer, LER BO, Concarneau, France. He received his PhD in 2009 from Ghent University. His research interests are the taxonomy, evolution, phylogeny, and biogeography of dinoflagellates, and the palaeoceanographical application of dinoflagellate cysts, particularly in the Quaternary and Neogene.

M. Consuelo Carbonell-Moore

M. CONSUELO CARBONELL-MOORE is a retired oceanographer, researching the morphology of tropical dinoflagellates at Oregon State University, in Corvallis, Oregon, USA. She has described several new genera and species of dinoflagellates. Her main focus is the study of the family Podolampadaceae Lindemann as well as rare dinoflagellates found in deep waters (shade species) in different tropical areas of the world’s oceans.

Kristina Gardner

KRISTINA GARDNER has a BSc in geology from Morehead State University, where her undergraduate thesis was on fungal palynomorphs from the PETM in Texas. Currently she is pursuing a master’s degree at the University of Delaware using dinoflagellate cysts, pollen and spores extracted from samples from the Paleocene–Eocene boundary in the central Delaware coastal plain. The aim is an environmental reconstruction of the nearshore to offshore transition to clarify the stratigraphy at the truncation of the Rancocoas aquifer in Kent County, Delaware.