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.
Highlights
Over time, evolution has produced impressive biodiversity in the world’s oceans, including multicellular organisms, such as animals, and unicellular organisms that make significant ecological c ontributions[1,2]
The posterior sulcal plate abuts the first postcingular plate in Peridiniales, whilst this contact is usually absent in Gonyaulacales
Planktonic cells with elongated processes are rare among extant dinophytes, and three types can be readily distinguished: (a) delicate, unbranched, and filiform setae of Micracanthodinium Deflandre; (b) robust, striated, and intratabular processes present in Acanthodinium Kof. and Cladopyxis; (c) slender processes that are randomly distributed over the cell surface and not associated with particular thecal plates
Summary
Evolution has produced impressive biodiversity in the world’s oceans, including multicellular organisms, such as animals, and unicellular organisms that make significant ecological c ontributions[1,2]. Foraminifers, and radiolarians are iconic unicellular groups, in which our knowledge of their biodiversity is far from complete Another key group of planktonic organisms are the Dinophyceae, which have great ecological and economic importance because of their different nutrition types and the toxicity of a considerable number of species[3,4,5]. The original species description by Friedrich von Stein[10] was accompanied by drawings (here reproduced as Fig. S1) These drawings illustrate cells with heterogeneous morphologies and thecal processes that vary in number and shape, which can be either long or short and distally undivided, bifurcate, or multi-branching. The Cladopyxidaceae (Dinophyceae) comprise small microalgae distributed in marine, (sub)tropical h abitats[8,13] They are morphologically well circumscribed but to this day, knowledge of their life-history and molecular characteristics is still very limited. The sexiform hypotheca represents the ancestral character state for Gonyaulacales present in a paraphyletic grade, but it is the partiform hypotheca that was considered rare and exclusive to the Cladopyxidaceae in extant dinophytes[8,18]
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