Phagotrophic Mechanisms and Prey Selection in Free-living Dinoflagellates1

Three types of feeding mechanisms are known in dinoflagellates: pallium feeding, tube feeding, and direct engulfment. Pallium feeding has only been described for heterotrophic thecate species (Protoperidinium, Diplopsalis group). Tube feeding is commonly found among both naked and thecate species of mixotrophic and heterotrophic dinoflagellates (e.g. Amphidinium, Dinophysis, Gyrodinium, Peridiniopsis). Direct engulfment is mainly found among naked species (e.g. Gymnodinium, Gyrodinium, Noctiluca): recently, however, some thecate species have been shown to use this feeding mechanism as well. Feeding behavior in dinoflagellates involves several steps prior to actual ingestion, including precapture, capture, and prey manipulation. As feeding mechanisms allow the ingestion of relatively large prey or parts thereof, dinoflagellates are regarded as raptorial feeders. While prey size plays an important role in the ability of dinoflagellates to ingest food, this alone cannot explain observed prey preferences. Some dinoflagellate species can be very selective in their choice of prey, while others show a remarkable versatility.     

Diel feeding pattern and prey selection of mesozooplankton on microplankton community

Mesozooplankton play an important role in transporting energy from microphytoplankton and microzooplankton to higher trophic levels. However there were few studies on the diel feeding patterns and prey selectivity of mesozooplankton. We conducted feeding experiments of mesozooplankton in the East China Sea to determine their respective diel feeding patterns on diatoms, ciliates and dinoflagellates, and to assess the contribution of these prey items to mesozooplankton diet. The results showed higher mesozooplankton grazing rates on ciliates and dinoflagellates than on diatoms at the day time, and the opposite pattern at the night time. A significant prey selection was observed, in which mesozooplankton positively selected ciliates and dinoflagellates during day and diatoms at night. The different grazing reactions of mesozooplankton toward each prey item might be related to the mobility of the prey. In all, microzooplankton (ciliates and dinoflagellates) provided the majority of the mesozooplankton carbon ingestion, even at a station dominated by small pennate diatoms. In particular, dinoflagellates are an important prey of mesozooplankton in the East China Sea and their contribution to the diet of mesozooplankton is unproportionate to their abundance.     

Some Morphogenetic Factors in Taxonomy of Dinoflagellates

The formative ability of ectoplasm in situ and in isolation from the living cell is shown to be an autodynamic morphogenetic factor creating sui generis membrane structure in species. Heteromorphic division and formation of specific aberrants, which differ from the parent cell by characters which have been used to separate genera, may be caused by molecular changes in ectoplasm as a primary factor. The subpellicular vacuom reticulum in Gyrodinium and other genera originates possibly from the upset metabolism of protoplasm. It is purely phenotypic. Oxygen deficiency induces in Prorocentrum endogenous cysts and dwarf-cell formation, a plasmolysis-like effect. The morphological norm in dinoflagellates is maintained also by the angle of nuclear fission and ensuing cytoplasm disposition. It is constant in sea and culture in some species, almost constant in sea but multivariable in culture in other species. The static form in some species is related to a single method of division (Exuviaella marina). Polymorphy of Exuviaella, Prorocentrum and other genera is induced by the presence of many types of divisions, which also favours an abundance of aberrants. “Osmomorphoses” originate in critical salinity-temperature conditions owing to flexibility of the pellicle in Gymnodinioideae; it is prevented by the membrane rigidity in the thecate forms. Flexibility of membrane in juvenile cells favours exogenous division. Rigid membranes of adult cells inhibit exogenous, favour endogenous fission. “Cyclomorphoses”, “phagomorphoses” (feeding habit) and different types of aberrants are useful to complete classification in modern and fossil dinoflagellates since morphogenesis rules work regardless of time and space.     

EARLY EVOLUTIONARY HISTORY OF DINOFLAGELLATES AND APICOMPLEXANS (ALVEOLATA) AS INFERRED FROM HSP90 AND ACTIN PHYLOGENIES1

Three extremely diverse groups of unicellular eukaryotes comprise the Alveolata: ciliates, dinoflagellates, and apicomplexans. The vast phenotypic distances between the three groups along with the enigmatic distribution of plastids and the economic and medical importance of several representative species (e.g. Plasmodium, Toxoplasma, Perkinsus, and Pfiesteria) have stimulated a great deal of speculation on the early evolutionary history of alveolates. A robust phylogenetic framework for alveolate diversity will provide the context necessary for understanding the basic biological properties of the group and for developing appropriate strategies for management. We addressed the earliest stages of alveolate evolution by sequencing heat shock protein 90 (hsp90) genes from several ciliates, apicomplexans, and dinoflagellates, including key species thought to represent early diverging lineages: Oxyrrhis marina, Perkinsus marinus, Cryptosporidium parvum, and the eugregarine Monocystis agilis. Moreover, by sequencing the actin gene from Monocystis, we were able to examine the sister relationship between gregarines and cryptosporidians with a three‐protein concatenated data set (hsp90, actin, and β‐tubulin). Phylogenetic analyses of the hsp90 data set provided a robust topology for alveolate relationships: Alveolates were monophyletic and apicomplexans and dinoflagellates formed sister groups to the exclusion of ciliates. Oxyrrhis formed the earliest diverging sister lineage to the “core” dinoflagellates, and Perkinsus formed the earliest diverging sister lineage to the Oxyrrhis–dinoflagellate clade. This topology was strongly supported inall analyses and by a unique indel shared by Oxyrrhis and dinoflagellates. A sister relationship between Cryptosporidium and Monocystis was weakly supported by the hsp90 data set but strongly supported by the three‐protein concatenated data set.     

WIDESPREAD PHAGOCYTOSIS OF CILIATES AND OTHER PROTISTS BY MARINE MIXOTROPHIC AND HETEROTROPHIC THECATE DINOFLAGELLATES1

An electron microscopic examination of large amorphous inclusions located in a variety of photosynthetic thecate dinoflagellates (Alexandrium ostenfeldii (Paulsen) Balech et Tangen, Gonyaulax diegensis Kofoid, Scrippsiella sp., Ceratium longipes (Bailey) Gran, and Prorocentrum micans Ehrenberg) and a nonphotosynthetic thecate species (Amylax sp.) revealed each inclusion to be a food vacuole, the majority of which were ingested ciliate prey. Recognizable features of these ciliates included linear arrays of basal bodies and cilia consistent with oligotrich polykinetid structure, characteristic macronuclei, chloroplasts (evidently kleptoplastids), cup-shaped starch plates, and cylindrical extrusomes. Three species contained (apparent) nonciliate prey: Scrippsiella sp., whose food vacuoles consistently contained unusual and complex extrusome-like cylindrical bodies having a distinctive six-lobed, multilayered structure; P. micans, which contained an unidentified encysted cell; and a single A. ostenfeldii cell, containing a Dinophysis sp. dinoflagellate cell. Several food vacuoles of ciliate origin had a red hue. This, together with the resemblance of A. ostenfeldii cells to planozygotes, suggests that similar structures previously identified as accumulation bodies may in fact be food vacuoles and that feeding may in some cases be associated with sexual processes.     

甲藻的异养营养型

综述了甲藻的异养类型。目前已知异养营养型在甲藻中广泛存在,只有很少几种甲藻营严格自养营养方式。有近一半的甲藻物种是没有色素体的,还有很多甲藻即使具有色素体也会有异养营养需求,称为兼养营养类型。这些兼养类群不一定主要以有机物作为其获取碳的来源,而仅仅是补充一些生长必需的有机物如维生素、生物素等。兼养类群以渗透营养和腐食营养方式进行,同时也可以寄生方式和共生方式进行兼养生活。无色素体的甲藻以有机物作为碳的唯一来源,仅仅依靠异养方式生存,属于严格异养营养方式,又称有机营养型。它们是甲藻异养营养型的主体,其主要类型有寄生、渗透营养和吞噬营养。由于吞噬营养是甲藻异养的主要类型,因此论述了3种吞噬营养型:吞噬营养方式、捕食茎营养方式和捕食笼营养方式。吞噬营养方式在无甲类和具甲类甲藻中都有存在,主要通过甲藻细胞的纵沟或底部对猎物进行吞噬,也有研究发现吞噬部位为顶孔或片间带。捕食茎营养方式是通过捕食茎刺穿猎物细胞膜并吸食其细胞质来获取营养,在异养甲藻中也较常见。捕食笼营养方式只在原多甲藻属(Protoperidinium)和翼藻属(Diplopsalis)里发现,是甲藻通过鞭毛孔分泌细胞质到胞外形成捕食笼将猎物包裹并进行消化来摄食的。甲藻摄食对象尺寸范围变化较大,小至几微米,大至几百微米。有些甲藻具有摄食选择性,通过感应猎物释放的化学物质来判断猎物的位置并进行摄食,摄食完成后由于体积的增加经常会发生细胞分裂和蜕鞘。对于甲藻异养的其他形式如拦截摄食营养方式、伪足摄食营养方式、口足摄食营养方式、触手摄食营养方式等只作简单介绍。还就甲藻异养的研究方法、其生态学意义和进化学意义进行简要论述,并对相关研究进行展望。     

Relationship between the flagellates and the ciliates.

The flagellates and the ciliates have long been considered to be closely related because of their unicellular nature and the similarity in the structures of the axoneme of the flagella and cilia in both groups. Most protozoologists believe that the ciliates arose from a flagellate. The flagellates that are most similar in structure to the ciliates are the dinoflagellates and two genera of uncertain taxonomic position, Colponema and Katablepharis. Structurally, dinoflagellates have a number of similarities with ciliates. These include the similarity of the cortical alveoli in the ciliates to the thecal vesicles in the dinoflagellates, the possession of tubular cristae, the similarity of the parasomal sac of the ciliates to the pusule of the dinoflagellates, the possession of similar trichocysts and mucocysts, and some similarity in the feeding apparatus. Colponema spp. are probably related to the dinoflagellates and have many of the same similarities with the ciliates. Katablepharis spp. are very similar in structure to the swarmer (embryo) of the suctorian ciliates. Indeed, reduction in the number of cilia to two in the suctorian swarmer and elimination of the macronucleus would result in a cell that is very similar to the Katablepharis cell. The feeding apparatus of Katablepharis spp. and the rest of the ciliates consists of two concentric microtubular arrays associated with vesicles. Information available from nucleotide sequencing of rRNA places the dinoflagellates in an ancestral position to the ciliates. The rRNA of Colponema and Katablepharis spp. has not yet been investigated. The use of stop codons in mRNA is discussed in relation to phylogeny.     

THE “HYSTRICHOSPHAERID” RESTING SPORE OF THE DINOFLAGELLATE PYRODINIUM BAHAMENSE,PLATF, 19062

Germination experiments demonstrate that the “hystrichosphere” called Hemicystodinium zoharyi, which previously has been found only as a microfossil organism, is the resting spore stage in the life history of Pyrodinium bahamense, a modern bioluminescent, thecate dinoflagellate. The morphology of this spore, together with new details of the thecal structure and ontogeny of P. bahamense, is described, and it is concluded that Pyrodinium is closely related to Gonyaulax but worthy of retention as a discrete genus. The geological history of P. bahamense is traceable to the Eocene through fossil occurrences of its spore, and it is suggested that additional pyrodinioid dinoflagellates which now are extinct were represented in Lower Tertiary seas by another hystrichosphere genus, called Homotryblium. Selected aspects of the physiology and ecology of modern dinoflagellate resting spores are discussed briefly with special reference to Pyrodinium.     

Search for Clues to the Evolutionary Meaning of Ciliate Phylogeny*†

SYNOPSIS. Progress in ciliatology and in allied fields may demystify ciliate phylogenetics. Concentration on hymenostomes (mainly Tetrahymena and Paramecium) may have obscured directional features of ciliate physiology in phylogenetic problems. Therefore, means are suggested for “domesticating” the presumptively primitive, predominantly marine, sand-dwelling gymnostomes having nondividing diploid macronuclei. The prize quarry is the marine psammophile Stephanopogon whose homokaryotic condition may mark it as a living fossil. Eventual axenic cultivation of these “primitive” ciliates may be aided by use as food of easily grown photosynthetic prokaryotes, some isolated from the marine sulfuretum or adjacent aerobic muds and sands where “karyorelictid” ciliates flourish. We assume that: (a) the macronucleus evolved as a coordinator of chemical and physical signals, for efficient detection of food and toxins; (b) oral structures evolved meanwhile as sensors as well as mechanical food-gatherers. This conjunction enabled complexity of adaptive behavior and evolutionary success. Ciliate origins cannot be considered apart from origin(s) of phagotrophy and its underlying versatile heterotrophy. Because of the well developed heterotrophy in some photosynthetic prokaryotes (including several proposed as food organisms), they are viewed as alternatives to blue-green algae as forebears of eukaryotes. Nor can ciliate origins be considered apart from origin(s) of eukaryotes. A check of these assumptions—that Stephanopogon and gymnostomes with nondividing macronuclei are primitive—may be forthcoming from sequencing amino acids in certain key enzymes, given an adequate sampling of ciliates, flagellates (especially dinoflagellates and cryptomonads), lower fungi, and photosynthetic prokaryotes other than blue-green algae.     

Biomass and Functional Distribution According to the Feeding Modes of Two Freshwater Protozoan Communities

The study has been made concerning the composition of and the relationships among: physico-chemical factors, abundance, number of species, biomass, heterotrophic and photoautotrophic components, and functional groups with regard to the feeding patterns of a river-reservoir system. The most outstanding results concerning the system as a whole are: 1, a relationship exists between the biomass of protozoa and the biomass of ciliates; 2, the most important functional groups, in terms of the number of species, are group III (ciliate “downstream” filter feeders) and group IV (ciliate “upxtream” filter feeders), and in terms of the abundance of specimens, the most important ones are groups III and V (raptorial feeders); 3, the division into functional groups according to feeding modes is similar in the river and the reservoir studied. This correlation is quite significant with regard to the number of species, the abundance of specimens, and between the samples taken from the two areas.     

Microzooplankton Growth Rates Examined across a Temperature Gradient in the Barents Sea

Growth rates (µ) of abundant microzooplankton species were examined in field experiments conducted at ambient sea temperatures (−1.8–9.0°C) in the Barents Sea and adjacent waters (70–78.5°N). The maximum species-specific µ of ciliates and athecate dinoflagellates (0.33–1.67 d⁻¹ and 0.52–1.14 d⁻¹, respectively) occurred at temperatures below 5°C and exceeded the µ_max predicted by previously published, laboratory culture-derived equations. The opposite trend was found for thecate dinoflagellates, which grew faster in the warmer Atlantic Ocean water. Mixotrophic ciliates and dinoflagellates grew faster than their heterotrophic counterparts. At sub-zero temperatures, microzooplankton µ_max matched those predicted for phytoplankton by temperature-dependent growth equations. These results indicate that microzooplankton protists may be as adapted to extreme Arctic conditions as their algal prey.     

FRESHWATER DINOFLAGELLATES OF BELIZE,C.A.

Freshwater dinoflagellates have not previously been reported from Belize, although there has been extensive work with marine dinoflagellates and some work with other freshwater groups. Freshwater dinoflagellates are more frequently observed in standing water and none have been observed in the several streams and rivers sampled since 1990. The goal in 1998 was to examine water samples from small ponds within hours of collection to improve the chance of observing swimming dinoflagellates. A plankton net was used and whole water samples also were collected. A small brown water pond on a peninsula and 30m from the Caribbean yielded a bloom of Thompsodinium intermedium. Dinoflagellates, including Peridinium centenniale, Katodinium sp., and Peridinium sp. in the Umbonatum Group, were observed within “Crocodile pond” and “Lily pond” on the mainland.     

Contribution of Ciliated Microprotozoans and Dinoflagellates to the diet of three Copepod species in the Bay of Biscay

Predation of three calanoid copepods (Calanus helgolandicus, Temora longicornis and Centropages chierchiae) on phytoplankton, dinoflagellates and ciliates was estimated in the Gironde estuarine plume (Bay of Biscay) during winter by means of in situ incubations. Both phytoplankton and ciliates were part of the diet of those three species, while only Centropages chierchiae also included a significant portion of dinoflagellates in its diet. The clearance rates of Calanus helgolandicus for ciliates and phytoplankton reached 2.8 and 4.0 ml copepod^–1 h^–1, respectively, those of Temora longicornis were 3.2 and 1.8 ml copepod^–1 h^–1, and those of Centropages chierchiae were 4.3 and 0.8 ml copepod^–1 h^–1.Neither Calanus helgolandicus nor Temora longicornis selected dinoflagellates, given the low clearance rates measured for this prey category (0.05 and 0.03 ml copepod^–1 h^–1, respectively). By contrast, Centropages chierchiae included dinoflagellates in its diet, with a clearance rate of 4.9 ml copepod^–1 h^–1. Within a given prey category (ciliates or dinoflagellates), all three copepods selected larger prey types (>40 m) over smaller ones (40 m). This implies a better detection and capture of larger motile prey compared to small ones. The results are discussed with regard to the omnivorous feeding behavior of these copepods observed here, during a late winter phytoplankton bloom.     

Syndinean dinoflagellates of the genus Euduboscquella are paraphyletic

Syndinean dinoflagellates of the genus Euduboscquella infect marine ciliates and dinoflagellates. Euduboscquella species infecting dinoflagellates are understudied relative to congeners infecting ciliates and their molecular phylogeny remains uncertain. Morphology, development, and rRNA gene sequences of intracellular parasites infecting heterotrophic dinoflagellates from coastal waters of Busan, Republic of Korea in summer to fall of 2019–2021 indicate that Cucumeridinium coeruleum, Gyrodinium cf. ochraceum, and two unidentified species of Gyrodinium were each infected by a different Euduboscquella species. Morphological features including shield structure, shape and color of the mature trophont, and sporogenic process distinguished each of the four parasites from the 10 previously described species of Euduboscquella. Our molecular and phylogenetic analyses showed considerably greater genetic distance of SSU and ITS-LSU rRNA gene regions among Euduboscquella species infecting dinoflagellates than among those infecting ciliates. Rather than clustering as a group with Euduboscquella species infecting ciliates, SSU rRNA sequences of the four novel parasites spread out across the syndinean Group I phylogeny, occurring in two different clades and a new lineage. Placement of our novel parasites in multiple clades that encompass Ichythyodinium chabelardi strongly indicates that the genus Euduboscquella is paraphyletic.     

Mixotrophy among Dinoflagellates1

Mixotrophy, used herein for the combination of phototrophy and phagotrophy, is widespread among dinoflagellates. It occurs among most, perhaps all, of the extant orders, including the Prorocentrales, Dinophysiales. Gymnodiniales, Noctilucales, Gonyaulacales, Peridiniales, Blastodiniales. Phytodiniales, and Dinamoebales. Many cases of mixotrophy among dinoflagellates are probably undocumented. Primarily photosynthetic dinoflagellates with their “own” plastids can often supplement their nutrition by preying on other cells. Some primarily phagotrophic species are photosynthetic due to the presence of kleptochloroplasts or algal endosymbionts. Some parasitic dinoflagellates have plastids and are probably mixotrophic. For most mixotrophic dinoflagellates, the relative importance of photosynthesis, uptake of dissolved inorganic nutrients, and feeding are unknown. However, it is apparent that mixotrophy has different functions in different physiological types of dinoflagellates. Data on the simultaneous regulation of photosynthesis, assimilation of dissolved inorganic and organic nutrients, and phagotophy by environmental parameters (irradiance. availablity of dissolved nutrients, availability of prey) and by life history events are needed in order to understand the diverse roles of mixotrophy in dinoflagellates.     

Maternal feeding strategies, child eating behaviors, and child BMI in low-income African-American preschoolers

Objective: To test the hypothesis that low‐income African‐American preschool children would have a higher BMI if their mothers reported greater “restriction” and “control” in feeding and if mothers reported that children showed greater “food responsiveness” and “desire to drink.” In addition, to test whether higher maternal “pressure to eat” would be associated with lower child BMI. Research Methods and Procedures: A questionnaire was completed by 296 low‐income African‐American mothers of preschool children. It assessed three constructs on maternal feeding strategies (“restriction,” “pressure to eat,” and “control”) and two on child eating behaviors (“food responsiveness” and “desire to drink”). Children's BMI was measured, and mothers’ BMI was self‐reported. Results: The mean (standard deviation) BMI z‐score of the children was 0.34 (1.5), and 44% of the mothers were obese (BMI ≥30 kg/m²). Only maternal “pressure to eat” had a significant overall association with child BMI z‐score (r = ?0.16, p < 0.01). Both maternal “restriction” and “control” were positively associated with children's BMI z‐score in the case of obese mothers (r = 0.20, p = 0.03 and r = 0.24, p = 0.007, respectively), but this was not so in the case of non‐obese mothers (r = ?0.16, p = 0.05 and r = ?0.07, p = 0.39, respectively). Discussion: Among low‐income African Americans, the positive association between maternal restriction and control in feeding and their preschoolers’ BMI was limited to obese mothers. Relations between parent feeding strategies and child weight status in this population may differ on the basis of maternal weight status.     

Composition,diversity and distribution of microbenthos across the intertidal zones of Ryazhkov Island (the White Sea)

The composition and distribution of the main unicellular eukaryotic groups (diatom algae, ciliates, dinoflagellates (DF), other phototrophic (PF) and heterotrophic flagellates (HF)) were investigated in sandy sediments at five stations allocated across the tidal sheltered beach of the White Sea. Overall, 75 diatoms, 98 ciliates, 16 DF, 3 PF and 34 HF species were identified; some are new records for the White Sea. Common species for each group are illustrated. Diatoms and ciliates showed high alpha-diversity (species richness per sample), whereas flagellates were characterized by high beta-diversity (species turnover across the intertidal flat). Each group demonstrated its own spatial pattern that was best matched with its own subset of abiotic variables, reflecting group-specific responses to environmental gradients. Species richness increased from the upper intertidal zone seaward for ciliates but decreased for HF, whereas autotrophs showed a relatively uniform pattern with a slight peak at the mid-intertidal zone. Across the littoral zone, all groups showed distinct compositional changes; however, the position of the boundary between “upper” and “lower” intertidal communities varied among groups. Most of the species found at Ryazhkov Island are known from many other regions worldwide, indicating a wide geographic distribution of microbial eukaryotic species.     

Parasitic Life Styles of Marine Dinoflagellates1

Several genera of marine dinoflagellates contain species that have evolved parasitic life styles. Dinoflagellate infections have been reported for a wide range of host organisms including sarcodines. ciliates, free-living dinoflagellates, various invertebrates, and a few vertebrates. Some dinoflagellates even parasitize other parasitic dinoflagellates. Most species are obligately parasitic and rely on heterotrophy as their sole means of nutrition; however, some are mixotrophic, as they possess chloroplasts during part or all of their life cycle. Many are ectoparasites that use highly specialized structures to attach to their host and feed, while others are intracellular parasites that feed by osmotrophy. Parasitic dinoflagellates often have adverse effects on their host that can lead to reproductive castration or death. The ecological importance of parasitic dinoflagellates is particularly evident during epidemic outbreaks that cause mass mortality of host organisms. Species that infect fish can pose threats to aquaculture. while other species can make commercially important crustacea unpalatable. In the planktonic realm, parasitic dinoflagellates influence the structure and function of the microbial food web. They compete with copepods and other grazers by utilizing ciliates as hosts and can stimulate rapid recycling of nutrients by causing the decline of toxic and non-toxic red tides.     

Morphological and molecular characterization of Ptychodiscus noctiluca revealed the polyphyletic nature of the order Ptychodiscales (Dinophyceae)

The planktonic dinoflagellate Ptychodiscus noctiluca combined distinctive morphological features such as a disk‐shaped anteroposteriorly compressed cell body and an apical carina, together with a flexible and tough cell covering, suggesting intermediate characteristics between thecate and naked dinoflagellates. Ptychodiscus noctiluca was examined by light, epifluorescence, and scanning electron microscopy from specimens collected in the Mediterranean Sea and the North and South Atlantic Ocean. Ptychodiscus noctiluca showed a straight apical groove that bisected the carina, a cell covering with a polygonal surface reticulum, nucleus without capsule, sulcal intrusion in the episome, sulcal ventral flange, and yellowish‐green chloroplasts that are shared characters with Brachidinium/Karenia. The cell division was the typical binary fission of gymnodinioid dinoflagellates, although exceptionally in an oblique transversal axis. We examined the intraspecific variability during incubation experiments. In the fattened cells, termed as Ptychodiscus carinatus, chloroplasts transformed into dark granules, and the cell acquired the swollen and smaller stage, termed as P. inflatus. Ptychodiscus carinatus, P. inflatus, and Diplocystis antarctica are synonyms of P. noctiluca. Molecular phylogeny based on the SSU rDNA sequence revealed that Ptychodiscus branched within the short‐branching dinokaryotic dinoflagellates as an independent lineage with affinity to Brachidinium/Karenia and Karlodinium/Takayama in a generally poorly resolved clade. Our results indicated that the order Ptychodiscales, established for unarmored dinoflagellates with a strongly developed pellicle, has artificially grouped thecate dinoflagellates (Kolkwitziella, Herdmania), naked dinoflagellates with thick cell covering (Balechina, Cucumeridinium) and other insufficiently known unarmored genera with typical cell coverings (Brachidinium, Ceratoperidinium).