Abstract
Biomineralization in calcareous dinophytes (Thoracosphaeracaea, Peridiniales) takes place in coccoid cells and is presently poorly understood. Vacuolar crystal-like particles as well as collection sites within the prospective calcareous shell may play a crucial role during this process at the ultrastructural level. Using transmission electron microscopy, we investigated the ultrastructure of coccoid cells at an early developmental stage in fourteen calcareous dinophyte strains (corresponding to at least ten species of Calciodinellum, Calcigonellum, Leonella, Pernambugia, Scrippsiella, and Thoracosphaera). The shell of the coccoid cells consisted either of one (Leonella, Thoracosphaera) or two matrices (Scrippsiella and its relatives) of unknown element composition, whereas calcite is deposited in the only or the outer layer, respectively. We observed crystal-like particles in cytoplasmic vacuoles in cells of nine of the strains investigated and assume that they are widespread among calcareous dinophytes. However, similar structures are also found outside the Thoracosphaeraceae, and we postulate an evolutionarily old physiological pathway (possibly involved in detoxification) that later was specialized for calcification. We aim to contribute to a deeper knowledge of the biomineralization process in calcareous dinophytes.
Highlights
Biomineralization is defined as the fundamental biological process by which living organisms produce minerals, often to harden or stiffen existing tissues or subcellular organic matrices
The biomineralization process and its structural basis are well understood in metazoans including mollusks, corals, and vertebrates [5,6,7], and in such protists as foraminifers and coccolithophores [8,9,10]
In the calcareous dinophytes (Thoracosphaeraceae, Peridiniales), it is the shell of the coccoid cells that is mineralized by calcitic crystals [11,12]
Summary
Biomineralization is defined as the fundamental biological process by which living organisms produce minerals, often to harden or stiffen existing tissues or subcellular organic matrices. In the calcareous dinophytes (Thoracosphaeraceae, Peridiniales), it is the shell of the coccoid cells that is mineralized by calcitic crystals [11,12]. As the potential to form calcareous structures is unique within the entire alveolates, it has been considered an apomorphic character trait supporting the monophyly of the Thoracosphaeraceae [17]. This assumption has gained some corroboration from molecular sequence data, a number of (presumably secondarily) non-calcareous taxa might be included in this group [18,19,20]. Molecular phylogenies segregate calcareous dinophytes into three main lineages, namely the E/Pe-clade (for Ensiculifera Balech, 1967 and Pentapharsodinium Indel. & A.R.Loebl.), the T/Pf-clade (for Thoracosphaera Kamptner and Pfiesteria Steid. & J.M.Burkh.), and Scrippsiella Balech ex A.R.Loebl. sensu lato (s.l.)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
