Morphological and molecular characterization of Ptychodiscus noctiluca revealed the polyphyletic nature of the order Ptychodiscales (Dinophyceae)

Abstract

The planktonic dinoflagellate Ptychodiscus noctiluca combined distinctive morphological features such as a disk-shaped anteroposteriorly compressed cell body and an apical carina, together with a flexible and tough cell covering, suggesting intermediate characteristics between thecate and naked dinoflagellates. Ptychodiscus noctiluca was examined by light, epifluorescence, and scanning electron microscopy from specimens collected in the Mediterranean Sea and the North and South Atlantic Ocean. Ptychodiscus noctiluca showed a straight apical groove that bisected the carina, a cell covering with a polygonal surface reticulum, nucleus without capsule, sulcal intrusion in the episome, sulcal ventral flange, and yellowish-green chloroplasts that are shared characters with Brachidinium/Karenia. The cell division was the typical binary fission of gymnodinioid dinoflagellates, although exceptionally in an oblique transversal axis. We examined the intraspecific variability during incubation experiments. In the fattened cells, termed as Ptychodiscus carinatus, chloroplasts transformed into dark granules, and the cell acquired the swollen and smaller stage, termed as P. inflatus. Ptychodiscus carinatus, P. inflatus, and Diplocystis antarctica are synonyms of P. noctiluca. Molecular phylogeny based on the SSU rDNA sequence revealed that Ptychodiscus branched within the short-branching dinokaryotic dinoflagellates as an independent lineage with affinity to Brachidinium/Karenia and Karlodinium/Takayama in a generally poorly resolved clade. Our results indicated that the order Ptychodiscales, established for unarmored dinoflagellates with a strongly developed pellicle, has artificially grouped thecate dinoflagellates (Kolkwitziella, Herdmania), naked dinoflagellates with thick cell covering (Balechina, Cucumeridinium) and other insufficiently known unarmored genera with typical cell coverings (Brachidinium, Ceratoperidinium).

High contribution of Rhizaria (Radiolaria) to vertical export in the California Current Ecosystem revealed by DNA metabarcoding

“…Increased abundance of autotrophic dinoflagellates has also been observed in the Point Conception region during years of delayed upwelling [24]. Consistent with this, our molecular survey revealed high sequence abundance of P. noctiluca (Supplementary Table S3 and Figure S6), a dinoflagellate species with distinctive cell covering characteristics and widespread distribution [78] that is generally less common in the CCE. Among green algae, the dominance of prasinophytes clade VII-B1 (Chloropicophyceae), a group typical of offshore waters [45], over Mamiellophyceae, characteristics of coastal waters, is another indication of the oceanic characteristics of the epipelagic zone.…”

Oxytoxaceae are prorocentralean rather than peridinialean dinophytes and taxonomic clarification of heterotrophic Oxytoxum lohmannii (≡ “Amphidinium” crassum) by epitypification

“…The Ptychodiscales, but not the Gymnodiniales, include also the Brachydiniaceae, confirming once more deliberate morphological concepts of the pre-DNA era 38 . The fact that these relationships have not been recognised so far 41 is mainly due to the gain of only short sequences (e.g., Ptychodiscus with SSU information only), the inferior single gene analyses already mentioned and the use of taxon samples that are not representative for the known molecular diversity of dinophytes.…”

The function of the ocelloid and piston in the dinoflagellate Erythropsidinium (Gymnodiniales, Dinophyceae)

“…Methods of collection and observation were described in Gómez et al. () and in Appendix in the Supporting Information. The aim of the observations at Marseilles and Banyuls‐sur‐Mer was to obtain the first molecular data of Erythropsidinium in order to resolve its phylogenetic affiliation (Gómez et al.…”