Morphology, ultrastructure and molecular phylogeny of <i>Johsia chumphonensis</i> gen. et sp. nov. and <i>Parvodinium parvulum</i> comb. nov. (Peridiniopsidaceae, Dinophyceae)

The family Peridiniopsidaceae encompasses mainly freshwater species of the genera <i>Peridiniopsis, Palatinus</i> and <i>Parvodinium</i>. Only one benthic, marine species ‘<i>Scrippsiella</i>’ <i>hexapraecingula</i> has been attributed to this family. Here we established five strains by isolating single <i>Parvodinium</i>-like cells from the marine Gulf of Thailand, Hainan Island waters (China), off Manado (Indonesia) and from a freshwater reservoir in Fuzhou (China). All strains were examined with light, scanning and transmission electron microscopy, and their SSU, ITS-5.8S and partial LSU rRNA regions were sequenced. Four marine strains share a plate formula of Po, cp, X, 4′, 2a, 6′′, 6C, 4S, 5′′′, 2′′′′ and are herein attributed to a new genus <i>Johsia</i> as <i>J. chumphonensis</i> gen. et sp. nov. Its theca is characterized by an epitheca 1.5 times as long as the hypotheca in dorsal view and a 2a plate about half the size of 1a. A type B eyespot was observed in <i>J. chumphonensis</i> comprising two rows of lipid globules within a chloroplast with a single row of crystals overlying the eyespot. Production of spherical cysts was observed in culture. The freshwater strain shows a plate pattern of Po, cp, X, 4′, 2a, 7′′, 6C, 5S, 5′′′, 2′′′′, characterized by two unequal antapical plates and a lack of antapical spines, fitting the description of <i>Peridinium parvulum</i>, which was transferred to <i>Parvodinium</i> as <i>P. parvulum</i> comb. nov. In this species, a type A eyespot was observed comprising four rows of lipid globules within a chloroplast. A molecular phylogeny was inferred based on concatenated data from SSU, ITS-5.8S and partial LSU rRNA gene sequences using maximum likelihood and Bayesian inference. Our results show that <i>Johsia</i> is nested within the Peridiniopsidaceae and is a sister clade to <i>Peridiniopsis borgei</i> and the strain UTEX1948 identified as ‘<i>Scrippsiella</i>’ <i>hexapraecingula</i> with three anterior intercalary plates.