An autotrophic unarmored dinoflagellate species with haptophyte-derived plastids, Kapelodiniopsis flava n. g., n. sp., was described as a sister taxon of Kapelodinium vestifici, which was formerly well characterized by its low-positioned cingulum and heterotrophic nature. The isolates from several Japanese coastal locations were observed using light microscopy, scanning and transmission electron microscopy, and their phylogeny was inferred from nuclear-encoded rRNA genes and multiple plastid-encoded genes. To date of this publication, a representative culture of Ks. flava has grown autotrophically for 98 months in the absence of prey or organic matter. This dinoflagellate lacked nonplastid haptophyte cell components (e.g. nucleus or mitochondria). In the host dinoflagellate phylogeny, Ks. flava was distantly related to the other two dinoflagellate lineages known to be associated with haptophyte-derived plastids, thus representing the third of such lineage. Plastid origins differed among Ks. flava strains (>99.8% 18S rRNA gene identity), with plastids being derived from at least three haptophytes and an especially strong genetic similarity to two distantly related extant haptophytes (>99.9% 16S rRNA gene identity). This indicates that Ks. flava recently integrated plastids from multiple haptophyte lineages to an extent that allows the host to replicate the plastids without other haptophyte components.
Keywords: Katodinium; culture; endosymbiosis; kleptoplastidy; molecular phylogeny; plastid membranes; plastid replacement; relic plastid; taxonomy; ultrastructure.
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