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

Abstract

The family Peridiniopsidaceae encompasses mainly freshwater species of the genera Peridiniopsis, Palatinus and Parvodinium. Only one benthic, marine species 'Scrippsiella' hexapraecingula has been attributed to this family. Here we established five strains by isolating single Parvodinium-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 Johsia as J. chumphonensis 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 J. chumphonensis 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 Peridinium parvulum, which was transferred to Parvodinium as P. parvulum 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 Johsia is nested within the Peridiniopsidaceae and is a sister clade to Peridiniopsis borgei and the strain UTEX1948 identified as 'Scrippsiella' hexapraecingula with three anterior intercalary plates.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.

Establishing a new genus, Chiharadinium gen. nov. (Peridiniales, Dinophyceae) for a tidal pool dinoflagellate formerly known as Scrippsiella hexapraecingula

“…The tree recovered here indicated a close relationship between this organism and the genus Johsia (based on J. chumphonensis) which is supported by some shared cytological features, including the possession of a Type B eyespot and a stalked type of pyrenoid. The thecal plate arrangement of the genus Johsia differs from that of C. hexapraecingulum by having two rather three anterior intercalaries, although they share the same number of precingular plates (Luo et al 2021). The phylogenetic tree currently recovered showed a closer affiliation of C. hexapraecingulum with P. borgei than with Johsia and the differences in episomal arrangement and habitat between these two organisms (Horiguchi & Chihara 1983;Luo et al 2021) make it inappropriate to accommodate C. hexapraecingulum in the genus Johsia.…”

“…(2020) and Luo et al . (2021). These authors designated this strain (EF492509) as ‘ Scrippsiella ’ hexapraecingula .…”

“…The thecal plate arrangement of the genus Johsia differs from that of C. hexapraecingulum by having two rather three anterior intercalaries, although they share the same number of precingular plates (Luo et al . 2021). The phylogenetic tree currently recovered showed a closer affiliation of C. hexapraecingulum with P. borgei than with Johsia and the differences in episomal arrangement and habitat between these two organisms (Horiguchi & Chihara 1983; Luo et al .…”

“…Our molecular phylogenetic analysis revealed that of the organisms represented, Chiharadinium hexapraecingulum is most closely related to the type species of the genus Peridiniopsis, P. borgei, a freshwater dinoflagellate. The strain UTEX1948 designated as Peridinium sociale, has been reported to be closely related to Peridiniopsis borgei by Kretschmann et al (2020) and Luo et al (2021). These authors designated this strain (EF492509) as 'Scrippsiella' hexapraecingula.…”

“…Based on the studies using culture strain UTEX1948, this species was identified to be S. hexapraecingula by Horiguchi and Chihara (1983). The UTEX1948 sequence has subsequently been shown to be closely related to that of Peridiniopsis borgei (Kretschmann et al 2020;Luo et al 2021).…”