Abstract
In alveolate evolution, dinoflagellates have developed many unique features, including the cell that has epicone and hypocone, the undulating transverse flagellum. However, it remains unclear how these features evolved. The early branching dinoflagellates so far investigated such as Hematodinium, Amoebophrya and Oxyrrhis marina differ in many ways from of core dinoflagellates, or dinokaryotes. Except those handful of well studied taxa, the vast majority of early branching dinoflagellates are known only by environmental sequences, and remain enigmatic. In this study we describe two new species of the early branching dinoflagellates, Psammosa pacifica n. g., n. sp. and P. atlantica n. sp. from marine intertidal sandy beach. Molecular phylogeny of the small subunit (SSU) ribosomal RNA and Hsp90 gene places Psammosa spp. as an early branch among the dinoflagellates. Morphologically (1) they lack the typical dinoflagellate epicone–hypocone structure, and (2) undulation in either flagella. Instead they display a mosaïc of dinokaryotes traits, i.e. (3) presence of bi-partite trychocysts; Oxyrrhis marina–like traits, i.e. (4) presence of flagellar hairs, (5) presence of two-dimensional cobweb scales ornamenting both flagella (6) transversal cell division; a trait shared with some syndineansand Parvilucifera spp. i.e. (7) a nucleus with a conspicuous nucleolus and condensed chromatin distributed beneath the nuclear envelope; as well as Perkinsus marinus -like features i.e. (8) separate ventral grooves where flagella emerge and (9) lacking dinoflagellate-type undulating flagellum. Notably Psammosa retains an apical complex structure, which is shared between perkinsids, colpodellids, chromerids and apicomplexans, but is not found in dinokaryotic dinoflagellates.
Highlights
Alveolates are a major eukaryotic assemblage that includes three large and well-studied lineages, apicomplexans, dinoflagellates, and ciliates [1,2]
Concluding Remarks In this study, we report a new lineage of early-diverging dinoflagellates, which we name Psammosa, with description of two new species of P. pacifica and P. atlantica
Psammosa displays a range of interesting morphological characteristics further supporting its divergence early in the evolution of dinoflagellates
Summary
Alveolates are a major eukaryotic assemblage that includes three large and well-studied lineages, apicomplexans, dinoflagellates, and ciliates [1,2]. A number of unusual molecular innovations have been found to be universal among dinokaryotes, including unusual organisation of organelle genomes [8,9,10,11,12,13,14], and messenger RNAs with spliced leaders [15,16,17]. How these features evolved and relate to the evolution of their apicomplexan relatives is, not clear from the study of dinokaryotes alone: to understand the evolution of such features, a greater knowledge of the whole dinoflagellate diversity is required
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