Abstract
The genusCentrodiniumcontains oceanic and predominantly tropical species that have received little attention. Three species ofCentrodiniumwere examined using thecal plate dissociation, scanning electron microscopy, and molecular sequences. The apical horn ofCentrodinium intermediumandC. eminensis formed by the elongation of the fourth apical plate, and a second apical split into two plates. InC. punctatumtwo apical plates (2′ and 4′) almost completely encircle the apical pore plate (Po), while the contact with the plate 1′ in the ventral side is much reduced, and the plate 3′ does not reach the Po. Moreover, its left posterior lateral sulcal plate is longer than its right pair, while reversed in the typicalCentrodiniumspp. The sulcal posterior plate ofC. punctatumis located in the left-ventral side below the plates 1′′′ and 2′′′, while the sulcal posterior plate located in the right face below the plates 4′′′ and 5′′′ in the typicalCentrodiniumspp. Phylogenetic analyses based on the small and large subunit of the rRNA gene showed thatCentrodiniumspp. andAlexandrium affine/A. gaarderaeclustered as a sister clade of theAlexandrium tamarense/catenella/fraterculusgroups. The clade of the subgenusGessnerium, and the clade of the type species ofAlexandrium,A. minutum, with four divergent species, clustered in more basal positions. The polyphyly ofAlexandriumis solved with the split into four genera: (1)Alexandriumsensu stricto for the species of the clade ofA. minutumand four divergent species; (2) the reinstatement of the genusGessneriumfor the species of the clade ofA. monilatum; (3) the reinstatement of genusProtogonyaulaxfor the species of thetamarense/catenella/fraterculusgroups, and (4) the new genusEpisemicolongen. nov. forA. affineandA. gaarderae.New combinations in the generaGessnerium,Protogonyaulax,andEpisemicolonare proposed.
Highlights
Dino agellates are ubiquitous protists that play diverse roles in marine ecosystems
Centrodinium punctatum was the most abundant species compared with other congeneric taxa. e cells were slightly laterally flattened with a rhomboid shape
Species such as C. punctatum have the same plate formula of Alexandrium (Figures 1, 6(e)). e most typical apical pore plate of Alexandrium has a comma-shaped pore surrounded by marginal pores, and the chain-forming species have an anterior attachment pore [18]. e apical pore plate of Alexandrium is larger (>6 μm), and we can observe an oval or comma-shaped pore. e formation of the apical horn of Centrodinium implies a reduction of the surface available for the apical pore plate (
Summary
Dino agellates are ubiquitous protists that play diverse roles in marine ecosystems. Numerous studies are focused on species that are responsible for harmful algal blooms (HABs) in coastal waters. Paralytic shell sh poisoning (PSP) is generally regarded as the most well-known and widespread HAB syndrome, and is associated with toxins produced by certain dinoagellate species in the genus Alexandrium [1]. Whilst neritic species of the planktonic Alexandrium or the epiphytic Gambierdiscus, responsible for toxic events, have received considerable attention, other open-ocean gonyaulacoid dinoagellates remain under-investigated because of the paucity of material due to their low densities. E neritic HAB species of Alexandrium are typically non- or slightly compressed species, without horns or spines [2], while the oceanic gonyaulacoid dino agellates have horns and spines (Ceratocorys spp., Gonyaulax taylorii, etc.), and/or the cells are o en attened (i.e. Gonyaulax paci ca, [3]). Kofoid [3] described the genus Centrodinium for oceanic species characterized by a high laterally attened cell body with an apical and an antapical horn. Kofoid [3] described the genus Murrayella for three types
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