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ABSTRACTExtant species of the dinoflagellate genus Gonyaulaxare capable of producing resting cysts morphologically similar to different cyst-based genera, and their cyst-theca relationships are far from resolved. Here we have carried out germination experiments on several living cysts that resemble Spiniferites delicatusfrom the subtropical regions of China and Mexico. Both cyst and theca morphology were examined by light and scanning electron microscopy. A new species, Gonyaulax pospelovana, is described, characterized by a cingulum displacement and an overhang of twice its width, and two short antapical spines. The cysts of G. pospelovanahad a granular surface and gonal processes with petaloid tips. Maximum likelihood and Bayesian inference analyses based on LSU and SSU rRNA gene sequences revealed that strains identified as G. pospelovanawere monophyletic, forming a sister clade to Gonyaulax ellegaardiaeand several presumable strains of Gonyaulax spinifera. One Chinese strain and two Mexican strains of G. pospelovanawere examined for yessotoxin production using LC-MS/MS, but were not found to produce a detectable amount of toxins. Metabarcoding targeting the 18S V4 rRNA gene was performed on monthly collected samples in Xiamen Bay, China. A ZOTU (zero-radius operational taxonomic units) was detected that was consistent with G. pospelovana. Its maximum abundance was recorded in summer. Additionally, an OTU was identified as G. pospelovanafrom the Tara Oceans metabarcoding data, which occurred in the Indian and Pacific oceans at temperatures ranging from 28°C to 31°C, suggesting that it is a warm water species.

ABSTRACTSix strains of three different Gonyaulaxspecies were established by isolating cells from the Korean coastal area and the East China Sea, and their morphologies and molecular phylogenies based on SSU and LSU rRNA gene sequences were examined. In addition, the growth responses of the Gonyaulaxspecies to changes in temperature and salinity were investigated. Based on morphological features and phylogenetic positions, Gonyaulax whaseongensisand G. polygrammawere identified, and G. geomunensis sp. nov. is proposed in this study. These species displayed the plate formula typical for Gonyaulax, but G. polygrammaand G. geomunensissometimes showed a small intercalary plate (1a) surrounded by plates 2’, *3’ and 3’’. G. geomunensiswas morphologically characterized by an S-type ventral organization, descending with a displacement of one cingulum width and bearing one, two or three prominent antapical spines of similar size. The cell surface, which was distinct from other Gonyaulaxspecies, was thick and heavily reticulated into numerous polygonal areas. The reticulation was deeply excavated. The phylogenetics revealed that G. geomunensisand G. whaseongensisbelong to different clades, and that there are two ribotypes of G. polygramma, which were morphologically indistinguishable. These species had a close phylogenetic relationship to G. hyalina, and all of them were characterized by dextral torsion. G. whaseongensis, G. polygrammaand G. geomunensishad different growth responses to changes of temperature and salinity, respectively, indicating that morphological and phylogenetic identification of Gonyaulaxspecies can be supported by ecological niches.

ABSTRACTGonyaulax veriorwas initially described as Amylax diacanthafrom Belgian coastal waters a century ago but its detailed morphology needed restudy. Here, we established nine strains of G. veriorby germinating cysts or isolating cells from localities from the European Atlantic to the Caspian Sea and the Pacific Ocean. Both cyst and thecal morphology were examined by light and scanning electron microscopy. SSU, LSU and/or ITS-5.8S rRNA gene sequences were obtained from all strains. Cells of G. veriorhave a plate formula of Po, 4′, 2a, 6-7′′, 6C, 6S, 6′′′, 1p, 1′′′′ with an L-type ventral organisation, characterised by two either straight or curved antapical horns of variable length. Cysts of G. veriorare oval, smooth and contain one or two yellow accumulation bodies. The maximum-likelihood and Bayesian inference analyses based on SSU and LSU rRNA gene sequences revealed two clades of G. verior, referred to as ribotypes A and B. Genetic distances based on ITS-5.8S rRNA gene sequences within the same ribotype were less than 0.06, but greater than 0.32 between ribotypes. G. verioris reclassified as Sourniaea diacantha gen. et comb. nov., which is attributed to Lingulodiniaceae together with Pyxidinopsis, Lingulodiniumand Amylax. Our results suggest that Lingulodiniaceae can be separated from Protoceratiaceae and Gonyaulacaceae based on ventral organisation, apical complex, ventral pore and number of anterior intercalary plates. One strain of S. diacanthawas examined for yessotoxin production by LC-MS/MS but did not produce toxin.

ABSTRACTA Cochlodinium-like species was isolated from the Korean coast and examined by light microscopy and scanning electron microscopy (SEM). The species was characterised by cellular torsion, cingulum with 1.25 turns and sulcus with 0.25 turn, and a hemispherical hypocone. The nucleus was curved, and sausage-shaped, and there were small, dark grains distributed at the cell periphery, which were also reported in the original description of Gyrodinium flavescensby Kofoid & Swezy (1921). SEM observations revealed that the apical structure complex of the species formed a complete circle surrounding the cell apex, consisting of three parallel rows of vesicles; and that the outer rows, composed of small vesicles, were visible along the sides of cingulum. These morphological features were identical to those of Torquentidium convolutum. Phylogeny-based on small subunit and large subunit rDNA sequences, confirmed that the species was closely related to T. convolutumwithin the family Ceratoperidiniaceae. However, the species was distinct from T. convolutumby differences in cingulum and sulcus turn numbers, shape of hypocone in dorsal view and size. Based on morphological and phylogenetic analyses, we propose Torquentidium flavescens comb. nov.nested within the family Ceratoperidiniaceae.

ABSTRACTWe describe the life cycle, morphology and molecular phylogenetic position of Fragilidium mexicanum, based on vegetative cells established by incubation of resting cysts isolated from sediment trap samples collected at Jinhae–Masan Bay, Korea. Resting cysts of F. mexicanumwere spherical and surrounded by transparent mucilage, similar to other Fragilidiumspecies. Germinated vegetative cells were identified as F. mexicanumbased on thecal morphology and tabulation; the plate formula was Po, Pc, 4ʹ, 8″, 10c, 6s, 7ʹʹʹ, 1p, 2ʹʹʹʹ. Molecular phylogenetic analyses of sequence data for small and large subunits of ribosomal DNA genes revealed that Fragilidiumspecies were monophyletic with high supports and that F. mexicanumformed a separate clade with Fragilidiumsp. (JQ317599). Time-lapse photography was used to clarify the life history. Isolated resting cysts germinated into an unarmoured planomeiocyte and directly formed the pellicle cyst, with an armoured planomeiocyte emerging from the pellicle cyst. The armoured planomeiocyte underwent ecdysis and formed a coccoid meiocyte, with a two-celled chain emerging from the coccoid meiocyte. Like the armoured planomeicyte, vegetative cells also underwent ecdysis and then divided into two daughter cells that eventually emerged as motile vegetative cells. The life cycle of F. mexicanumhas nonmotile life history stages that regularly alternate with motile stages. The nonmotile stage consists of five forms: resting cyst, pellicle cyst, asexual coccoid stage, coccoid meiocyte, and zygote. The motile stage also has five forms: unarmoured and armoured planomeiocyte, planozygote, gamete and vegetative cell.

Abstract:Two morphologically distinct species, Brigantedinium majusculumand Trinovantedinium applanatum, have been suggested as a cyst stage of Protoperidinium pentagonum; however, the cyst–theca relationships are still virtually undefined. In this study, we re-examined the motile stage of B. majusculumvia thecal plate analysis together with a molecular phylogenetic analysis based on partial large-subunit ribosomal DNA gene sequences. The morphological features of motile cells germinated from B. majusculumwere identical to those of Pr. sinuosum, and the molecular phylogenetic analysis showed that the germinated cells and B. majusculumare closely related to Pr. pentagonumand Pr. latissimumas a sister group. Additionally, high sequence divergences were observed between the germinated cells and B. majusculumas well as Pr. pentagonumand Pr. latissimum(18.0–19.5% according to P-values and 20.7–22.9% according to Kimura two-parameter values). On the basis of these results, our study indicates that B. majusculumshould be accepted as the cyst of Pr. sinuosum.

Abstract:The genus Tovelliacontains approximately eight described species. A new species, Tovellia paldangensis sp. nov. was observed by incubation of a cyst from sediment collected in the Paldang Dam Lake in Korea. The vegetative cells of this new species were 20.0–27.0 μm long, 18.0–23.0 μm wide, and 17.0–20.5 μm thick. The cingulum was displaced by one cingulum width, the nucleus was located in the posterior part of the cell, and the chloroplasts were numerous and in yellow-green in color. A prominent red body was present on each side of the cingulum. The amphiesma had numerous thin polygonal plates that were arranged in three to four latitudinal series on the epicone and in two to three series on the hypocone. A narrow apical line of plates (ALP) extended over the anterior part of the cell, approximately in a 3/4 of the ventral side and 1/4 of the dorsal side of the epicone. The antapical plate was usually hexagonal. T. paldangensiswas clearly differentiated from the other species of Tovelliaby the morphology of its vegetative cell (two red bodies, and the ALP lines on each side separated by a row of four to five elongate plates) and the resting cyst (typically covered with numerous short solid spines). Phylogenetic analysis based on partial large subunit ribosomal RNA gene sequences indicated that T. paldangensiswas most closely related to T. coronata, T. sanguinea, and T. aveirensis.