Fensomea setacea, gen. & sp. nov. (Cladopyxidaceae, Dinophyceae), is neither gonyaulacoid nor peridinioid as inferred from morphological and molecular data

Abstract

Dinophyte evolution is essentially inferred from the pattern of thecal plates, and two different labelling systems are used for the important subgroups Gonyaulacales and Peridiniales. The partiform hypotheca of cladopyxidoid dinophytes fits into the morphological concepts of neither group, although they are assigned to the Gonyaulacales. Here, we describe the thecate dinophyte Fensomea setacea, gen. & sp. nov., which has a cladopyxidoid tabulation. The cells displayed a Kofoidean plate formula APC, 3′, 4a, 7″, 7C, 6S, 6′′′, 2′′′′, and slender processes were randomly distributed over the echinate or baculate surface. In addition, we obtained rRNA sequences of F. setacea, gen. & sp. nov., but dinophytes that exhibit a partiform hypotheca did not show a close relationship to Gonyaulacales. Character evolution of thecate dinophytes may have progressed from the ancestral state of six postcingular plates, and two more or less symmetrically arranged antapical plates, towards patterns of only five postcingular plates (Peridiniales) or more asymmetrical configurations (Gonyaulacales). Based on our phylogenetic reconsiderations the contact between the posterior sulcal plate and the first postcingular plate, as well as the contact between an antapical plate and the distalmost postcingular plate, do not represent a rare, specialized gonyaulacoid plate configuration (i.e., the partiform hypotheca of cladopyxidoid dinophytes). Instead, these contacts correspond to the common and regular configuration of peridinioid (and other) dinophytes.

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

“…Molecular phylogenetics of Prorocentrales have always been challenging, last not least due to the strong rate heterogeneity across the constituent taxa. However, prorocentralean dinophytes are monophyletic in DNA-trees using concatenated rRNA sequences 45 – 48 , though rarely statistically supported. The complete set of taxa belonging to the Prorocentrales as identified in the present study has not been shown before, but there is confidence that molecular trees will improve once longer rRNA sequences than the segments such as SSU are available, particularly for the deeply diverged branches also of prorocentralean dinophytes.…”

“…Moreover, prorocentralean members with five postcingular plates share a long suture between the proximate and the distal such plates, which is morphologically unique, possibly apomorphic here but different in all other dinophytes with this hypothecal plate pattern. A posterior intercalary plate is considered abundant in Gonyaulacales, but it can be also interpreted as first of the two widespread antapical plates 48 , 62 . Under this assumption, gonyaulacoid dinophytes have no posterior intercalary plate(s), which are otherwise rarely if at all found in dinophytes additionally to the prorocentralean members identified here.…”

Using RDNA sequences to define dinoflagellate species

“…D8-D10 regions in the analysis will only further strengthen the ability to delineate dinoflagellate species. This approach has been successfully employed by Gottschling et al, 2020Gottschling et al, , 2021.…”

Reply to: Comments on Mertens et al. (2022): the taxonomic identity of Micracanthodinium setiferum (Lohmann) Deflandre (Dinophyceae incertae sedis) remains elusive, and its epitypification is not achieved

“…However, it is well known that the setae in Micracanthodinium break easily (Dodge 1995). It is notable that in a close relative, Fensomea setacea , which also carries setae, scanning electron microscope (SEM) micrographs do not show the setae even though they are visible in the light microscope images, confirming that there is a change due to the preparations for SEM: there are some Fensomea cells shown without setae, and others with setae (Gottschling et al 2021, fig. 2).…”