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As historically described, the genus Amphidinum has long been recognized to be polyphyletic. Amphidinium sensu lato is the most diverse of all marine benthic dinoflagellate genera and after the redefinition of the sensu stricto genus about 100 species remained of unknown generic affiliation. A species similar to the Australian sensu lato species Amphidinium boggayum was discovered in France. Morphological and molecular phylogenetic data supported the description of a new species and the classification of the two closely related species within a new athecate, photosynthetic, benthic genus, named Bindiferia. Cells were dorsoventrally flattened with smaller asymmetric epicone. The cingulum was descending. The sulcus reached the antapex and had an extension onto the epicone. The apical structure complex formed an anticlockwise loop around the apex. A red stigma was located in the anterior part of the epicone, near the apex. Vegetative division occurred in a non-motile stage within a hyaline sheath. Non-motile cells had dorsal hypocone grooves. The two species differed from each other in epicone size, cingulum displacement, nucleus location and surface groove occurrence. The molecular phylogenetic results showed that Bindiferia is a distinct taxon that is only distantly related to Amphidinium sensu stricto. The nearest sister group to Bindiferia could not be reliably determined, but the apical structure complex suggested a close relationship to the genera of the Gymnodinium sensu stricto clade.

Benthic dinoflagellates produce a wide array of bioactive compounds, primarily polyketides, that cause toxic effects on human consumers of seafood and perhaps mediate species interactions in the benthic microenvironment. This study assesses toxic and other bioactive effects of the benthic dinoflagellate Amphidinium operculatum (strain AA60) in two targeted bioassays. The brine shrimp (Artemia salina) bioassay revealed lethal effects of direct exposure to live dinoflagellate cells (Treatment A) and even higher potency with ethanolic extracts of lysed cells (Treatment D). There were no inimical bioactive effects of components released to the aqueous growth medium (Treatment B) or from aqueous cell lysates (Treatment C). The hypothesis that released bioactive compounds provide a chemical defense against metazoan grazers is therefore not supported by these results. The cytotoxic effect of ethanolic crude extracts of this dinoflagellate exhibited mild to high growth reduction effects on six human cancer cell lines. In particular, crude cell-free extracts proved highly growth-inhibitory activity towards breast and lung cancer cell lines MCF-7 and SKLU-1, respectively. Preliminary anti-cancer results indicate that natural bioactive compounds from Amphidinium are worthy of structural characterization and further toxicological investigation as potential therapeutants.

Gymnodinium gracile, described from the coasts of Denmark in 1881, is one of the first described unarmored dinoflagellates. Individuals which morphologically fit with the original description were isolated from the English Channel (North‐East Atlantic). The SSU rRNA gene sequences were identical to the sequences identified as Balechina pachydermata and Gymnodinium amphora from the Mediterranean Sea and Brazil. We propose the transfer of Gymnodinium gracile into the genus Balechina as B. gracilis comb. nov. These sequences constitute an independent lineage, clustering with numerous environmental sequences from polar to tropical waters. The widespread distribution, the high plasticity in size, shape and coloration and the difficulties in discerning the fine longitudinal striae have contributed to the description of numerous synonyms: Amphidinium vasculum, Balechina pachydermata (=Gymnodinium pachydermatum), Gymnodinium achromaticum, G. abbreviatum, G. amphora, G. dogielii, G. lohmannii (=G. roseum sensu Lohmann 1908), G. situla and Gyrodinium cuneatum (=G. gracile sensu Pouchet 1885).

Many benthic dinoflagellates produce polyketide-derived polyether toxins responsible for diverse seafood poisoning syndromes, such as diarrhetic shellfish poisoning and ciguatera fish poisoning. In Mexico, bHAB events have received recent public health and scientific attention, but many species lack molecular identification, and phylogeographic and toxigenic information remains limited. Our multidisciplinary project on bHAB taxa includes morphological and molecular characterization, phylogeography, and investigation of allelopathic and pharmacological bioactivity, supplemented with bacterial microbiome analysis. We first characterized the phylogeography and diversity of the genus Prorocentrum from Mexican coasts and investigated potential allelochemical effects of associated bacteria on growth and toxigenicity of members of the Prorocentrum lima species complex. Thus far, we have also completed the first phylogenetic study of benthic Amphidinium and registered two species (A. theodorei and A. massartii) for the first time from Mexico. Preliminary studies on the in vitro cytotoxic properties of A. operculatum and Coolia malayensis are also well advanced, demonstrating pharmacological potential through bioactivity against human cancer cell lines. The focus on functional diversity and species interactions yields valuable insights in evaluating toxin risk in the design and implementation of monitoring systems for bHABs and exploring biotechnological prospects for bioactive secondary metabolites from benthic species.

Gibbosterol A (1), a water-soluble 14-membered carbocyclic steroid with a twisted trans-9,11-epoxy ring, was discovered from the South China Sea dinoflagellate, Amphidinium gibbosum, together with its acid-induced cyclization product 2. It exhibits marked agonistic effects against human pregnane-X-receptor in a dose-dependent manner within the concentration range of 100 nM to 10 μM. Its 5/14-carbobicyclic nucleus is proposed to be originated from late-stage oxidative cleavage of the C5-C10 and C8-C9 bonds of β-sitosterol.

A sailboat-shaped 20-membered macrolide, named gibbosolide A, featuring a rare cis-fused 2-methylhexahydro-2H-furo[3,2-b]pyran motif, was obtained from the South China Sea dinoflagellate, Amphidinium gibbosum. Its planar structure and absolute configuration, containing twelve carbon stereocenters, were unambiguously established by extensive NMR investigations, J-based configuration analysis, NOE interactions, ozonolysis of the carbon–carbon double bonds, and the modified Mosher's α-methoxy-α-(trifluoromethyl)phenylacetyl (MTPA) ester method. It displays activation effects on human farnesoid–X–receptor within the concentration range of 200.0 nM to 2.0 μM. Its late-stage cyclization mechanisms are proposed. Most notably, ozonolysis of the carbon–carbon double bonds combined with the modified Mosher's ester method is a useful approach for the unambiguous determination of absolute configurations of hydroxy-bearing carbon stereocenters within the complex macrolide core.

Two highly potent cytotoxic 26-membered macrolides, isocaribenolide-I (1) and a chlorohydrin 2, together with known amphidinolide N (3), have been isolated from a free-swimming dinoflagellate Amphidinium species (KCA09053 and KCA09056 strains) collected off Iriomote Island, Japan. The structures of 1 and 2 were determined to be a congener of 3 with an isobutyl terminus and the chlorohydrin form of 3, respectively, by detailed analyses of spectroscopic data. The relative stereochemistries of 1 and 2 were elucidated by the conformational analyses based on NMR data.

Waminoa sp. acoel flatworms hosting Symbiodiniaceae and the related Amphidinium dinoflagellate algae are an interesting model system for symbiosis in marine environments. While the host provides a microhabitat and safety, the algae power the system by photosynthesis and supply the worm with nutrients. Among these nutrients are sterols, including cholesterol and numerous phytosterols. While it is widely accepted that these compounds are produced by the symbiotic dinoflagellates, their transfer to and fate within the sterol-auxotrophic Waminoa worm host as well as their role in its metabolism are unknown. Here we used matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging combined with laser-induced post-ionization and trapped ion mobility spectrometry (MALDI-2-TIMS-MSI) to map the spatial distribution of over 30 different sterol species in sections of the symbiotic system. The use of laser post-ionization crucially increased ion yields and allowed the recording of images with a pixel size of 5 μm. Trapped ion mobility spectrometry (TIMS) helped with the tentative assignment of over 30 sterol species. Correlation with anatomical features of the worm, revealed by host-derived phospholipid signals, and the location of the dinoflagellates, revealed by chlorophyll a signal, disclosed peculiar differences in the distribution of different sterol species (e.g. of cholesterol versus stigmasterol) within the receiving host. These findings point to sterol species-specific roles in the metabolism of Waminoa beyond a mere source of energy. They also underline the value of the MALDI-2-TIMS-MSI method to future research in the spatially resolved analysis of sterols.

Two new macrolides, iriomoteolides-14a (1) and 14b (2) have been isolated from the marine dinoflagellate Amphidinium species (strain KCA09057). Compounds 1 and 2 are 15-membered macrolides, which are structural analogs of amphidinolides O (3) and P (4). The structures of 1 and 2 were assigned on the basis of detailed NMR analyses and chemical conversion studies. Compounds 1 and 2 showed moderate cytotoxic activity against human cervix adenocarcinoma HeLa cells.

After a 1.5 year screening survey in the lagoons of Western Greece in order to isolate and culture sturdy species of microalgae for aquaculture or other value added uses, as dictated primarily by a satisfactory potential for their mass-culture, five species emerged and their growth was monitored in laboratory conditions. Amphidinium carterae, Nephroselmis sp., Tetraselmis sp. (var. red pappas), Asteromonas gracilis and Dunaliella sp. were batch cultured using low (20 ppt), sea (40 ppt) and high salinity (50 or 60 or 100 ppt) and in combination with a low (2000 lux) and high (8000 lux) intensity of illumination. The results exhibited that all these species can be grown adequately in all salinities and with best growth in terms of maximum cell density, specific growth rate (SGR) and biomass yield (g dry weight/L) at high illumination (8000 lux). The five species examined exhibited different responses in the salinities used, Amphidinium clearly does best in 20 ppt far better than 40 ppt and even more than 50 ppt. Nephroselmis and Tetraselmis grow almost the same in 20 and 40 ppt and less well in 60 ppt. Asteromonas does best in 100 ppt although it can grow quite well in both 40 and 60 ppt. Dunaliella grows equally well in all salinities (20-40-60 ppt). Concerning productivity as maximum biomass yield at the end of the culture period, first rank is occupied by Nephroselmis with ~3.0 g d.w./L, followed by Tetraselmis (2.0 g/L), Dunaliella (1.58 g/L), Amphidinium (1.19 g/L) and Asteromonas (0.7 g/L) with all values recorded at high light (8000 lux).

There is growing interest in finding microalgae species that efficiently convert dissolved nutrients contained in aquaculture effluents into highly valuable biomass. The different nitrogen forms that are present in aquaculture effluents are particularly concerning. This study demonstrated that the dinoflagellate Amphidinium carterae can acclimate to both combined and sole nitrogen sources such as nitrate, ammonium, and urea over a wide concentration range. As far as is known, it is the first time that a species of the genus Amphidinium has been successfully cultured with urea as the sole source of nitrogen. In the presence of 882 μM of nitrate, A. carterae tolerated urea concentrations up to 5000 μM. With respect to ammonium-N tolerance, it has been observed that it is lethal at concentrations higher than 441 μM. A robust laboratory experimental design was critical for accurately assessing this acclimation. Alternative N sources did not affect the production of high-value specific polyketide secondary metabolites from A. carterae, such as amphidinols, with an average concentration of 0.435 ± 0.038% biomass d.w. An analysis of the symbiotic microbial assemblages developed in a long-term A. carterae culture in an open raceway pond, and the fact that it is able to metabolize all three nitrogen sources simultaneously, supports the idea that this microalga has the potential to be successfully cultured with aquaculture effluents.

Monthly phytoplankton samples were collected from January 2013 to December 2015 at a fixed sampling site in Bahia de La Paz, Gulf of California. During this study 26 samplings were Amphidinium cf. carterae positive. The highest densities of A. cf. carterae (754.2 × 103 to 1022.4 × 103 cells L−1) were recorded during a bloom detected in January 2015 when water temperatures were 20–22 °C. This dinoflagellate showed a well-marked seasonal variation, being found mainly from November to April. Blooms of the species were linked to the upwelled water due to the northwesterly wind. Cysts surrounded by a mucilaginous membrane of A. cf. carterae were found. We also observed these hyaline cysts inside zooplankton fecal pellets. Other benthic/tychoplanktonic dinoflagellates and diatoms, including some potentially toxic species were also found. The occurrence of blooms of A. cf. carterae in Bahia de La Paz could represent a risk for aquaculture activities and human health.

The present study investigated selected benthic dinoflagellates isolated from different regions from the Western Atlantic, with respect to their morphology, growth, toxicity, and toxin production in culture. A total of nine strains of benthic dinoflagellates belonging to three genera were cultivated: Amphidinium massartii, Amphidinium operculatum (2 strains), Coolia malayensis (2 strains), Prorocentrum hoffmannianum (2 strains), and Prorocentrum mexicanum, whose morphological and genetic characterizations matched previous descriptions, and Prorocentrum sp., morphologically related to P. cf. norrissianum. The two strains of C. malayensis from Brazil attained the highest growth rates (0.42–0.47 day−1), but the lowest cell densities (2.2–2.9 × 104 cells mL−1) in culture. The highest cell densities were recorded for A. massartii from Cuba (3.8 × 105 cells mL−1). All species/strains investigated exhibited moderate toxicity to larvae of the brine shrimp Artemia salina; A. massartii being the most toxic species and Prorocentrum sp. the least one. Additionally, extracts of Prorocentrum species (P. hoffmannianum and Prorocentrum sp.) tested positive in mouse bioassays following intraperitoneal injection. Moderate to high concentrations of okadaic acid (OA), but no dinophysistoxins (DTXs), were found in both P. hoffmannianum strains from Cuba; but no diarrheic toxins were detected in either P. mexicanum from Cuba or Prorocentrum sp. from southern Brazil. Finally, five novel amphidinols were detected in cultures of both A. massartii (Cuba) and A. operculatum (Brazil) by LC-MS/MS, with molecular weights of 1440.8 (two isomers), 1360.8, 1287.7, and 984.6. These findings clearly indicate the need to include benthic species among the harmful microalgae surveyed in regional monitoring programs of phytoplankton.

Sustainable dinoflagellate microalgae-based bioprocess designed to produce secondary metabolites (SMs) with interesting bioactivities are attracting increasing attention. However, dinoflagellates also produce other valuable bioproducts (e.g polyunsaturated fatty acids, carotenoids, etc.) that could be recovered and should therefore be taken into account in the bioprocess. In this study, biomass of the marine dinoflagellate microalga Amphidinium carterae was used to assess and optimise three different methods in order to obtain three families of high-value biochemical compounds present in the biomass. The existing processes encompassed a multi-step extraction process for carotenoids, fatty acids and APDs individually and are optimized for the integral valorization of raw A. carterae biomass, with SMs being the primary target compounds. Total process recovery yields were 97% for carotenoids, 80% for total fatty acids and 100% for an extract rich in APDs (not purified).

Biologically rich rock-pools (RPs) are prominent component of rocky intertidal habitat and this study elucidates the factors affecting the phytoplankton distribution from high-tide (HT), mid-tide (MT) and low-tide (LT) RPs (Anjuna rocky shores, Goa, India), during the summer season. Results revealed that the RP location determines the nature of phytoplankton assemblage. MT-RPs and LT-RPs supported rich microalgal diversity (species number/morphological shapes) than HT-RPs. However, the cell abundance was higher in latter than former RPs. In frequently flushed MT-RPs and LT-RPs, pennate diatoms (Pseudonitzschia, Nitzschia, Thalasionema, Navicula, and Licmophora) representing elongated shapes dominated, whereas in stagnant HT-RPs spherical/combined shaped dinoflagellates (Amphidinium carterae sensu stricto and Bysmatrum gregarium) dominated. Interestingly, even though the taxonomic assemblages changed temporally the shape dominance remained consistent suggesting shape as a robust morphological trait. Additionally, the study also revealed the existence of species-specific allelopathy on other microalgae by Amphidinium (potential harmful algae) indicating a type of adaptive strategy, in addition to eurytolerant capabilities, for its predominance in HT-RPs, which experiences varying environmental (light, temperature, and salinity) conditions.

Background Some dinoflagellates cause harmful algal blooms, releasing toxic secondary metabolites, to the detriment of marine ecosystems and human health. Our understanding of dinoflagellate toxin biosynthesis has been hampered by their unusually large genomes. To overcome this challenge, for the first time, we sequenced the genome, microRNAs, and mRNA isoforms of a basal dinoflagellate, Amphidinium gibbosum, and employed an integrated omics approach to understand its secondary metabolite biosynthesis. Results We assembled the ~ 6.4-Gb A. gibbosum genome, and by probing decoded dinoflagellate genomes and transcriptomes, we identified the non-ribosomal peptide synthetase adenylation domain as essential for generation of specialized metabolites. Upon starving the cells of phosphate and nitrogen, we observed pronounced shifts in metabolite biosynthesis, suggestive of post-transcriptional regulation by microRNAs. Using Iso-Seq and RNA-seq data, we found that alternative splicing and polycistronic expression generate different transcripts for secondary metabolism. Conclusions Our genomic findings suggest intricate integration of various metabolic enzymes that function iteratively to synthesize metabolites, providing mechanistic insights into how dinoflagellates synthesize secondary metabolites, depending upon nutrient availability. This study provides insights into toxin production associated with dinoflagellate blooms. The genome of this basal dinoflagellate provides important clues about dinoflagellate evolution and overcomes the large genome size, which has been a challenge previously.

This study concerns the finding of an effective operational equation relating the measured absorpbance (or O.D. - optical density) in a spectrophotometer of the suspended cells of microalgae to their cell density (c.d.) in culture in order to construct calibration curves for use in culture operations. The microalgae examined were the chlorophyte Nephroselmis sp., the dinophyte Amphidinium carterae and the filamentous cyanobacterium Phormidium sp. Wavelengths of 430 and 680 nm were selected that correspond to chlorophyll-a peaks of their absorption spectra were used and additionally 750 and 570 nm where absorbance was not peaked. From all equations extracted best fitness with strong predictive values were those of a logarithmic type: O.D.=0,9328*ln(c.d.)-14,108 (R2=0,9943) at 680 nm for Nephroselmis, a power equation: O.D.=0,0000009*(c.d.)0,9195 (R2=0,9936) at 680 nm for Amphidinium and a polynomial second order: O.D.=0,9869(c.d.)2+2,4393(c.d.)+0,2666 (R2=0,9737) at 570 nm for Phormidium.

Harmful algal bloom (HAB) events can have severe consequences such as mass fish kills and problems to public health. The Albion Fisheries Research Centre has an ongoing HAB monitoring programme at established coastal sites in Mauritius including Grand Baie, Albion, Le Morne and Blue Bay. The commonly observed benthic dinoflagellates are from the genera Amphidinium sp., Coolia sp., Gambierdiscus sp., Ostreopsis sp., Prorocentrum sp. and Synophysis sp. These are the causative agents of fish toxicity such as ciguatera. The monitoring data at the four monitoring sites for the period 2013–2017 were analysed to evaluate the temporal, spatial and seasonal variations in the densities of harmful marine microalgae species. Recurrent high densities were recorded at all the sites during the years. The genera Prorocentrum and Ostreopsis were observed at relatively higher densities throughout the years at the four study sites whilst the other genera occurred only occasionally. An increase in the mean cell densities of Ostreopsis sp. and Prorocentrum sp. were observed from 2013 to 2016 followed by a decline in the abundance in 2017 at most of the study sites. The cell densities of these two genera were found to be higher during summer seasons, and their occurrences were more significant at two sites, namely Blue Bay and Le Morne which are located in the South Coast of the Island. This warrants further studies to determine the influence of oceanographic parameters, seawater quality and environmental conditions on the cell densities of harmful marine microalgae in Mauritius.

Eukaryotic microalgae have developed CO2concentrating mechanisms to maximise the concentration of CO2 at the active site of Rubisco in response to the low CO2 concentrations in the external aquatic medium. In these organisms, the modes of inorganic carbon (Ci) uptake are diverse, ranging from diffusive CO2 uptake to the active transport of HCO3 -and CO2 and many have an external carbonic anhydrase to facilitate HCO3- use. There is unequivocal evidence for the mechanisms of Ci uptake in only about 25 species of microalgae of the chlorophyte, haptophyte, rhodophyte, diatom, and eustigmatophyte groups. Most of these species take up both CO2 and HCO3-, but the rates of uptake of each of these substrates varies with the algal species. A few species take up only one of the two forms of Ci, an adaptation that is not necessarily correlated with their ecological distribution. Evidence is presented for the active uptake of HCO3- and CO2 in two marine haptophytes,Isochrysis galbana Parke and Dicrateria inornata Parke, and for active transport of CO2 but lack of HCO3- uptake in two marine dinoflagellates, Amphidinium carteraeHulburt and Heterocapsa oceanica Stein.

For the first time, distribution of epiphytic dinoflagellates was studied in Saint Martin Island (Lesser Antilles) during the cyclonic season (between September 1st and 3rd, 2015). The present study provides a semi-quantitative analysis because the fresh weight of each macrophyte was estimated around 10 g. The identified genera were: Ostreopsis J.Schmidt, Prorocentrum Ehrenberg, Coolia Meunier, Amphidinium Claperede & Lachmann, and Gambierdiscus Adachi & Fukuyo in order of decreasing abundance. Highest average abundance values of the genera Ostreopsis and Amphidinium were hosted by macrophytes of the Phaeophyceae class with c. 15 000 and 60 cells g–1 respectively. Epiphytic Coolia cells were mainly observed on seagrasses with the highest average abundance value of c. 1000 cells g–1 whereas the genera Gambierdiscus and Prorocentrum were most often associated with Florideophyceae with the highest average abundances of c. 70 and 1500 cells g–1 respectively. This preliminary study indicates the most relevant locations to survey the biodiversity of potentially toxic epiphytic dinoflagellates in Saint Martin Island.

Ciguatera fish poisoning (CFP) is prevalent around the tropical and sub-tropical latitudes of the world and impacts many Pacific island communities intrinsically linked to the reef system for sustenance and trade. While the genus Gambierdiscus has been linked with CFP, it is commonly found on tropical reef systems in microalgal assemblages with other genera of toxin-producing, epiphytic and/or benthic dinoflagellates – Amphidinium, Coolia, Fukuyoa, Ostreopsis and Prorocentrum. Identifying a biomarker compound that can be used for the early detection of Gambierdiscus blooms, specifically in a mixed microalgal community, is paramount in enabling the development of management and mitigation strategies. Following on from the recent structural elucidation of 44-methylgambierone, its potential to contribute to CFP intoxication events and applicability as a biomarker compound for Gambierdiscus spp. was investigated. The acute toxicity of this secondary metabolite was determined by intraperitoneal injection using mice, which showed it to be of low toxicity, with an LD50 between 20 and 38 mg kg−1. The production of 44-methylgambierone by 252 marine microalgal isolates consisting of 90 species from 32 genera across seven classes, was assessed by liquid chromatography-tandem mass spectrometry. It was discovered that the production of this secondary metabolite was ubiquitous to the eight Gambierdiscus species tested, however not all isolates of G. carpenteri, and some species/isolates of Coolia and Fukuyoa.

Microhabitats influence the distribution and abundance of benthic harmful dinoflagellate (BHAB) species. Currently, much of the information on the relationships between BHABs and microhabitat preferences is based on non-quantitative anecdotal observations, many of which are contradictory. The goal of this study was to better quantify BHAB and microhabitat relationships using a statistically rigorous approach. Between April 2016 to May 2017, a total of 243 artificial substrate samplers were deployed at five locations in the Perhentian Islands, Malaysia while simultaneous photo-quadrat surveys were performed to characterize the benthic substrates present at each sampling site. The screen samplers were retrieved 24 h later and the abundances of five BHAB genera, Gambierdiscus, Ostreopsis, Coolia, Amphidinium, and Prorocentrum were determined. Substrate data were then analyzed using a Bray–Curtis dissimilarity matrix to statistically identify distinct microhabitat types. Although BHABs were associated with a variety of biotic and abiotic substrates, the results of this study demonstrated differing degrees of microhabitat preference. Analysis of the survey results using canonical correspondence analysis explained 70.5% (horizontal first axis) and 21.6% (vertical second axis) of the constrained variation in the distribution of various genera among microhabitat types. Prorocentrum and Coolia appear to have the greatest range being broadly distributed among a wide variety of microhabitats. Amphidinium was always found in low abundances and was widely distributed among microhabitats dominated by hard coral, turf algae, sand and silt, and fleshy algae and reached the highest abundances there. Gambierdiscus and Ostreopsis had more restricted distributions. Gambierdiscus were found preferentially associated with turf algae, hard coral and, to a lesser extent, fleshy macroalgae microhabitats. Ostreopsis, almost always more abundant than Gambierdiscus, preferred the same microhabitats as Gambierdiscus and were found in microbial mats as well. With similar habitat preferences Ostreopsis may serve as an indicator organism for the presence of Gambierdiscus. This study provides insight into how BHAB-specific microhabitat preferences can affect toxicity risks.

A study describing unrecorded and taxonomically undescribed indigenous species is in progress since 2006. Samples were collected from many sites in coastal waters and offshore of Korea as well as from Jeju Island. Since 2008, we have found ten unrecorded species of four genera belonging to family Dinophysaceae, Gonyaulacaceae, Gymnodiniaceae, and Heterocapsaceae. The species are as follows, Dinophysis elongata (2016 winter), D. nasuta (2016 winter), Gonyaulax alaskensis (2016 winter), G. diegensis (2017), G. monospina (2008), Amphidinium flagellans (2017), Heterocapsa circularisquama (2017), H. horiguchii (2017), H. lanceolata (2017), and H. pygmaea (2017) (note; The numbers in the parenthesis refer to the year in which the species was reported as unrecorded indigenous species by National Institute of Biological Resources, NIBR hereafter). Among them, seven species were described as newly recorded species in Korean waters, and three have been re-described in this study.

Marine dinoflagellate microalgae belonging to the genus Amphidinium are a key source of an interesting group of polyketide metabolites with potent bioactivities, wide-ranging functional diversity and stereochemical complexity, but low natural availabilities. The feasibility of a microalgae dinoflagellate-based sustainable bioprocess for producing amphidinols (APDNs) by photoautotrophic culture of Amphidinium carterae in a pilot-scale LED-illuminated bubble column photobioreactor (PBR) was therefore investigated. A fed-batch culture mode with pulse feeding strategy provided a growth pattern strongly limited by the availability of phosphate content in the culture medium that stimulated the production of cellular APDNs. Since A. carterae was found to be much more shear-sensitive than other shear-tolerant non-dinoflagellate microalgae, the culture height and air flow rate were established to ensure the absence of damaging levels of hydrodynamic stress. The biomass capacity yielded by the PBR at the end of the culture (0.540 g d.w. L−1 equivalent to 1.70 × 106 cell mL−1) corresponded to that estimated stoichiometrically from the experimentally determined biomass P-molar formula (C329 O126 H732 N69 S3 P1) and the total phosphorus and nitrogen balances. The downstream processing section was initially conceived to recover APDNs excreted by cells into the supernatant. A dry APDN-enriched extract concentration of 49 mg per liter of supernatant was obtained. This purification process led to partitioning of the extract into several fractions and sub-fractions thereof. Only two sub-fractions were studied, yielding thereof highly pure (>95% pure) luteophanol D and lingshuiol A, and a new, roughly purified (>80% pure) APDN, namely amphidinol 20. The percentages of luteophanol D, lingshuiol A and amphidinol 20 by dry weight of the APDN-enriched extract obtained were 1%, 0.39% and 0.31%, respectively, thus representing a concentration in the culture supernatant of 490, 191 and 152 μg L−1, respectively.

After a 1.5-year screening survey in the lagoons of Western Greece in order to isolate and culture sturdy species of microalgae for aquaculture or other value-added uses, as dictated primarily by satisfactory potential for their mass culture, five species emerged, and their growth was monitored in laboratory conditions. Amphidinium carterae, Nephroselmis sp., Tetraselmis sp. (var. red pappas), Asteromonas gracilis, and Dunaliella sp. were batch cultured using low (20 ppt), sea (40 ppt), and high salinity (50 or 60 or 100 ppt) and in combination with low (2000 lux) and high (8000 lux) intensity illumination. The results exhibited that all these species can be grown adequately in all salinities and with the best growth in terms of maximum cell density, specific growth rate (SGR), and biomass yield (g dry weight/L) at high illumination (8000 lux). The five species examined exhibited different responses in the salinities used, whereby Amphidinium clearly performs best in 20 ppt, far better than 40 ppt, and even more so than 50 ppt. Nephroselmis and Tetraselmis grow almost the same in 20 and 40 ppt and less well in 60 ppt. Asteromonas performs best in 100 ppt, although it can grow quite well in both 40 and 60 ppt. Dunaliella grows equally well in all salinities (20, 40, 60 ppt). Concerning the productivity, assessed as the maximum biomass yield at the end of the culture period, the first rank is occupied by Nephroselmis with ~3.0 g d.w./L, followed by Tetraselmis (2.0 g/L), Dunaliella (1.58 g/L), Amphidinium (1.19 g/L), and Asteromonas (0.7 g/L) with all values recorded at high light (8000 lux).

The calcium carbonate plates (coccoliths) surrounding most coccolithophorid cells are strikingly reminiscent of armor, and defense against predators has been hypothesized as a selective advantage provided by these mineral structures. Although microzooplankton are the main predators of small phytoplankton such as coccolithophores, few putative phytoplankton defenses have been tested against this group. In this study, predation by the heterotrophic dinoflagellate Amphidinium longum on three calcifying strains of Emiliania huxleyi was compared with predation on cells acid-treated to remove coccoliths. As a control for acidification effects on other cell properties, we also compared predation on acid-treated and untreated non-calcifying (haploid) E. huxleyi strains. We found no systematic support for the defense hypothesis in this predator-prey system. Acid-treated cells experienced predation rates that were higher, the same as, and lower than rates on untreated cells, depending on E. huxleyi strain. Other cell properties showing no relationship to predation included size, dimethylsulfoniopropionate (DMSP) content, and DMSP release. For untreated cells, however, hydrogen peroxide (H2O2) concentration in the cell suspension was positively related to predation, suggesting that H2O2 acts as a signal promoting prey detection, or that H2O2 co-varies with other (unmeasured) predation-enhancing cell properties. A. longum uses two different prey capture and ingestion strategies, depending on prey type. This plasticity suggests co-evolution of predation and defense strategies, facilitating a generalist feeding strategy compatible with the diversity of potential phytoplankton prey.

The genus Amphidinium is an important group of athecated dinoflagellates because of its high abundance in marine habitats, its member's ability to live in a variety of environmental conditions and ability to produce toxins. Furthermore, the genus is of particular interest in the biotechnology field for its potential in the pharmaceutical arena. Taxonomically the there is a history of complication and confusion over the proper identities and placements of Amphidinium species due to high genetic variability coupled with high morphological conservation. Thirteen years has passed since the most recent review of the group, and while many issues were resolved, some remain. The present study used microscopy, phylogenetics of the 28S region of rDNA, secondary structure of the ITS2 region of rDNA, compensatory base change data, and cytotoxicity data from Amphidinium strains collected world-wide to elucidate remaining confusion. This holistic approach using multiple lines of evidence resulted in a more comprehensive understanding of the morphological, ecological, and genetic characteristics that are attributed to organisms belonging to Amphidinium, including six novel species: A. fijiensis, A. magnum, A. paucianulatum, A. pseudomassartii, A. theodori, and A. tomasii.

Iriomoteolides-9a (1) and 11a (2), new 15- and 19-membered macrolides, respectively, have been isolated from the marine dinoflagellate Amphidinium species (strain KCA09052). Compounds 1 and 2 were obtained from the extracts of the algal cells inoculated in the PES and TKF seawater medium, respectively. The structures of 1 and 2 were assigned on the basis of detailed NMR analyses. Compounds 1 and 2 exhibited cytotoxic activity against human cervix adenocarcinoma HeLa cells.

A new marine benthic dinoflagellate, Testudodinium magnum sp. nov., was described from a sand sample collected on the seafloor at a depth of 35 m off Mageshima Island, Kagoshima, Japan. The dinoflagellate possessed the characteristic features of the genus Testudodinium, but was distinguished by its extremely large size and pebbled dorsal surface of the hyposome, caused by the presence of numerous nodules. The cells of this dinoflagellate possessed a dominant sessile and a rare motile form that were morphologically distinct from each other: The sessile form was larger and the small rounded episome with longitudinal furrow was completely embedded in the hyposome; the motile form was smaller and the episome was only partly embedded in the hyposome. The ultrastructural investigations revealed the presence of a large, circular, starch-sheathed pyrenoid whose matrix was traversed by randomly arranged thylakoid lamellae. The chloroplasts formed a network radiating outward from the pyrenoid. Uniquely, t...

Dinoflagellates are an extremely diverse group of unicellular eukaryotes that represent an important part of marine plankton communities. Among other secondary metabolites, these microorganisms are known to produce toxins such as the saxitoxins, karlotoxins, amphidinolides, okadaic acid or brevetoxins, which are extremely toxic for marine fauna and ultimately humans who consume contaminated seafood. The extreme biodiversity of dinoflagellates undoubtedly mirrors an inexhaustible reservoir of compounds, yet the chemodiversity of dinoflagellates is still poorly studied, due in part to constraints linked to the difficulty of isolating and cultivating these organisms. Nevertheless, an increasing number of new dinoflagellate secondary metabolites have been described in recent years. Here, we review these new advances in the isolation and characterization of bioactive metabolites from several dinoflagellates (Gymnodiniales, Amphidinium, Karlodinium, Karenia), Peridiniales (Vulcanodinium), Gonyaulacales (Alexandrium, Gambierdiscus, Ostreopsis), Prorocentrales (Prorocentrum) and Dinophysiales (Dinophysis).

Ciguatera fish poisoning is a frequently reported non-bacterial food-borne illness related to the consumption of seafood contaminated with ciguatoxins, and possibly maitotoxins. These toxins are synthesized by marine dinoflagellate species of Gambierdiscus and Fukuyoa genera, and their abundance is a matter of great concern due to their adverse effects to aquatic life and human health. The present study aims to assess the sensitivity of rat cardiomyoblast H9c2(2−1) cells to Gambierdiscus toxic compounds using concentration- and time-dependent sulforhodamine B (SRB) colorimetric assays. Low concentrations of Gambierdiscus extracts (corresponding to 1.3–2.3 cells mL−1) induced a concentration-dependent response. Specificity in time-dependent response of H9c2(2−1) cells was demonstrated for G. excentricus after a 180 min exposure compared to both G. cf. belizeanus and G. silvae species, with EC50s obtained after 720 and 360 min, respectively. The sensitivity of H9c2(2−1) cells to dinoflagellate toxic compounds was also tested with other genera from benthic (Coolia malayensis, Ostreopsis cf. ovata, Prorocentrum hoffmannianum and P. lima) and planktonic (Amphidinium carterae and Lingulodinium polyedrum) habitats. Amphidinium, Coolia and Lingulodinium data did not present any concentration-response relationships, and EC50 values could only be obtained after 720 and 1440 min of exposure to both Prorocentrum species and O. cf. ovata, respectively. This study demonstrated that the H9c2(2−1) SRB assay represents a promising and sensitive tool for the detection of Gambierdiscus toxic compounds present in water samples, particularly of G. excentricus at very low cell abundances.

Benthic dinoflagellates produce a diverse range of phycotoxins, which are responsible for intoxication events in marine fauna. This study assessed the hemolysis associated toxicities of six species of benthic dinoflagellates from the genera Coolia, Fukuyoa, Amphidinium and Prorocentrum. Results demonstrated that Amphidinium carterae, Coolia tropicalis and Fukuyoa ruetzleri were the three most toxic species, while Prorocentrum cf. lima did not have significant hemolytic effect. Grouper samples (Cephalopholis boenak) were more tolerant to the hemolytic algae than the blackhead seabream (Acanthopagrus schlegelii), with decreased heart rate and blood flow being observed in medaka larvae after exposure to toxic algal extracts. LC-MS/MS analysis detected a gambierone analogue called 44-methylgambierone produced by the C. tropicalis isolate. This analogue was also detected in the F. ruetzleri isolate. This study provided new information on the hemolysis associated toxicities of local toxic benthic dinoflagellates, which contributes to better understanding of their emerging threats to marine fauna and reef systems in Hong Kong.

The occurrence of toxic algal blooms and the environmental and commercial damage associated with these blooms appears to be on the increase globally. Toxic algal blooms are often known as red tides, as high enough concentrations of these phytoplankton may cause surface discolorations of the water body they are blooming in. Dinoflagellates and diatoms are commonly associated with red tide blooms, although other phytoplankton species are known to cause them. A number of reasons have been suggested for the apparent increase in these red tide blooms: increased utilization of coastal waters for aquaculture; stimulation of blooms by eutrophication and changes in climatological conditions; transport of toxic species worldwide in ballast water; and increased awareness of toxic species. Even though there is an increasing awareness and understanding of these species, current methods for detection and identification of toxic phytoplankton are inadequate.The classical method for identifying toxic algae is through the use of optical microscopy. However, size limitations and difficulties in observing and identifying morphological features means that even an expert can find it difficult to identify some of the smaller or more fragile species. Scanning Electron Microscopy is generally needed for unambiguous identification of toxic phytoplankton. However, difficulties with fixation of fragile algae, expense and limited access to SEM means that this method of identification is rarely used and is subject to some fundamental methodological problems. To establish an efficient monitoring system for waterways, it is imperative that a cheap, automated method of identification is developed.The most commonly used automated method of analysis for algae, flow cytometiy, is useful only for enumeration, sorting and identification of samples down to phylum. However, this thesis has demonstrated that the use of FT-IR microscopy combined with chemometrics (in particular PCA and linear discriminant analysis) shows promise as a useful tool for the rapid identification of toxic phytoplankton. Eight species of blooming phytoplankton were successfully differentiated using the method: Nitzschia closterium, Nitzschia frustulum, Skeletonema costatum, Skeletonema psuedocostatum, Nitzschia longissima, Peridinium balticum, Amphidinium caterae and Heterosigma carterae. Two groups of species that are almost identical morphologically (i.e. Nitzschia closterium / Nitzschia longissima and Skeletonema costatum/Skeletonema psuedocostatum were differentiated using this technique. The method is rapid and relatively inexpensive, and does not require the knowledge of an expert to undertake analysis as it is computer aided.Seven species of phytoplankton were grown in culture and one species (Nitzschia longissima) was collected from a bloom episode that occurred approximately 26 km downstream from the mouth of the Brisbane River. Spectra from early stationary stage cells were obtained for each species using an FT-IR microscope. Spectra were sorted into two groups depending upon the presence or absence of a strong peak at 1068 cm1. This peak is indicative of the large silica component contained in the diatom frustule, and hence was an initial method of sorting between the two groups for ease of data handling. PCA was then applied to each group and a number of classification methods were attempted to differentiate between the two groups. Mahalanobis distances, centroid and furtherest neighbour cluster analysis and k-means cluster analysis were of little use in differentiating between the species. However, discriminant analysis was able to differentiate between the species. 100 % of spectra of Nitzschia longissima, Skeletomena costatum, Skeletonema psuedocostatum, Peridinium balticum, Amphidinium caterae and Heterosigma carterae were classified correctly using this method. 69% of Nitszchia closterium and 61% of Nitzschia frustulum were correctly classified. First derivative and second derivative specthttps://espace.library.uq.edu.au/js/fckeditor/editor/images/spacer.gifra were also analysed, to little benefit.

Few studies have been carried out on benthic dinoflagellates along the Florida Keys, and little is known about their distribution or toxicity in Florida Bay. Here, the distribution and abundance of benthic dinoflagellates was explored in northern and eastern Florida Bay and along the bay and ocean sides of the Florida Keys. Isolates were brought into culture and their toxicity was tested with oyster larvae bioassays. Seven genera were detected, including Prorocentrum, Coolia, Ostreopsis, Amphidinium, Gambierdiscus, Fukuyoa (all included potentially toxic species) and Sinophysis. In general, distribution increased with water temperature and nutrient availability, especially that of phosphate. This study documented the first record of Coolia santacroce in the Florida Keys. Potential toxic effects of Gambierdiscus caribaeus, the abundance of which exceeded 1000 cells g−1 fw at some sites, were established using oyster larvae as a bioassay organism. These findings suggest a potential risk of ciguatera fish poisoning in this area.

Climate driven increases in ocean temperature and pCO2 have the potential to alter the growth and prevalence of future Harmful Algal Blooms (HABs), but systematic studies on how climate drivers influence toxic algal species relative to non-toxic phytoplankton are lacking. In particular, little is known about how future climate scenarios will affect the growth of the toxic dinoflagellate Alexandrium catenella, which is responsible for the paralytic shellfish poisoning (PSP) events that threaten the health and economy of coastal communities in the Gulf of Maine and elsewhere. The growth responses of A. catenella and two other naturally co-occurring dinoflagellates in the Gulf of Maine—Scrippsiella sp., and Amphidinium carterae—were studied in mono and mixed species cultures. Experimental treatments tested the effects of elevated temperature (20 °C), lower pH (7.8), and the combination of elevated temperature and lower pH on growth rates relative to those in near-current conditions (15 °C; pH 8.1). Growth rates of A. catenella decreased under elevated temperature and lower pH conditions, a response that was largely attributable to the effect of temperature. In contrast, growth rates of Scrippsiella sp. and A. carterae increased under elevated temperature and lower pH conditions, with temperature also being the primary driver of the response. These trends did not change substantially when these species were grown in mixed cultures (A. catenella + Scrippsiella sp., and A. catenella + A. carterae), indicating that allelopathic or competitive interactions did not affect the experimental outcome under the conditions tested. These findings suggest that A. catenella blooms may become less prevalent in the southern regions of the Gulf of Maine, but potentially more prevalent in the northeastern regions of the Gulf of Maine with continued climate change.

The seasonal and long-term dynamics of the species composition and abundance of dinoflagellates that live in subtidal sands in Russian waters of the Sea of Japan was studied for the first time. The overall species composition of sand-dwelling dinoflagellates in Peter the Great Bay was represented by 67 taxa that belong to 25 genera. Among them, 17 species were recorded for the first time from the seas of Russia, and 8 species were found from the Pacific coast of Russia for the first time. The greatest number of species belonged to the genera Amphidinium, Amphidiniopsis, and Thecadinium. A list of the species composition, including the distribution of taxa throughout the localities and seasons, is presented. Most species of the microalgae are illustrated by light and scanning electron micrographs. The species richness varied from 18 to 44 during the year. In the winter, at a water temperature less than 0°C, the species richness of sand-dwelling dinoflagellates (24–26 taxa) roughly coincided with that found in summer (20–44 taxa). The average density of dinoflagellates ranged from 16 to 1121 cells/cm3 across localities and throughout the year. During the annual cycle, the highest cell density (595 and 2576 cells/cm3) were recorded in the winter–spring period and a slight increase in abundance was observed in fall. This was due to the high cell densities of the dominant species Amphidiniopsis uroensis Toriumi, Yoshimatsu et Dodge, and Thecadinium kofoidii (E.C. Herdman) Larsen. Sand-dwelling dinoflagellates contributed 58 to 80% to the total annual density of the subtidal microphytobenthos in different localities of Peter the Great Bay.

A synthesis of the C8-C29 fragment of amphidinolide N, a potent cytotoxic macrolide isolated from the marine dinoflagellate Amphidinium sp., has been achieved. The key features of the synthesis involve a convergent union of the C9-C15 and C16-C29 fragments by Steglich esterification and the construction of a pyran unit through a Tebbe methylenation/ring-closing metathesis sequence.

One of the observed flagellates, Cryptella cyanophora Pascher, is probably the first discovery ever of this species with cyanelles after more than 80 years since its description. This species was previously classified into the cryptophycean genus Chroomonas Hansgirg (see Discussion), which is why the observations of two common species, Chroomonas nordstedtii Hansg. and Ch. caudata Geitler, from natural water bodies are also presented and the theory of their cytological evolution is discussed. Similar uncertainty is associated with the origin of blue-green chloroplasts of some dinoflagellates, two species of which (from Czech waters) are presented, namely Gymnodinium aeruginosum Stein and Amphidinium amphidinioides (Geitler) Schiller. Again the theory of the origin of their chloroplast is discussed. The indubitable syncyanosis is demonstrated on Glaucocystis nostochinearum Itzigsohn.

The genus of benthic dinoflagellates Ostreopsis is of particular interest because some species negatively impact human health and coastal marine ecosystems. Ostreopsis populations from a remote area, such as the Galapagos Marine Reserve with its unique biodiversity, can provide significant data. Samples of epibionthic dinoflagellates were collected from two islands (Santa Cruz and Santa Fé) in 2017. Species of the genera Gambierdiscus, Amphidinium, Coolia and Ostreopsis were found. Ostreopsis strains were isolated to characterize their morphology, molecular biology and toxicity. Three dif­ferent morphotypes of Ostreopsis based on dorsoventral and width diameters (n=369) were distinguished. The small cell morphotype was dominant in ten samples, with abundances of up to 33405 cells g-1 fresh weight of macroalgae. A total of 16 strains were isolated from field samples with subsequent polymerase chain reaction amplifications of rDNA, 5.8S rDNA and internal transcribed space regions; 13 strains (small cell morphotype) clustered in the O. cf. ovata Atlantic/Indian/Pacific clade; and 3 strains (large cell morphotype) clustered in the Ostreopsis lenticularis genotype from the type locality. The strains proved to be non-toxic. The presence of these genera/species represents a potential threat to marine ecosystems, and it is thus important to consider benthic species in the surveillance of harmful algae blooms in the reserve.

Coral reefs are some of the most important and ecologically diverse marine environments. At the base of the reef ecosystem are dinoflagellate algae, which live symbiotically within coral cells. Efforts to understand the relationship between alga and coral have been greatly hampered by the lack of an appropriate dinoflagellate genetic transformation technology. By making use of the plasmid-like fragmented chloroplast genome, we have introduced novel genetic material into the dinoflagellate chloroplast genome. We have shown that the introduced genes are expressed and confer the expected phenotypes. Genetically modified cultures have been grown for 1 year with subculturing, maintaining the introduced genes and phenotypes. This indicates that cells continue to divide after transformation and that the transformation is stable. This is the first report of stable chloroplast transformation in dinoflagellate algae.

Phycotoxins synthesized by benthic dinoflagellates are known to bioaccumulate in macrofauna and hence represent a risk for human health. However, the presence of toxins synthesized by benthic dinoflagellates in smaller marine organisms than macrofauna has not been considered despite the fact that such small organisms have an important ecological role in the benthic food web. This present study quantified, for the first time, the trophic relationship between benthic dinoflagellates and meiofauna by using stable isotope enriched dinoflagellates during ingestion experiments. Results showed that harpacticoid copepods were not able to discriminate, during ingestion, between the potentially toxic cells of Ostreopsis cf. ovata and the non-toxic cells of Amphidinium cf. carterae, even when another food resource, such as diatoms (e.g. Odontella sp.), was provided (Kruskal Wallis test, p > 0.05).

Two new macrolides, iriomoteolides-10a (1) and -12a (2), have been isolated from a marine dinoflagellate Amphidinium sp. (KCA09053 strain), and their structures were elucidated on the basis of a detailed two dimensional (2D)-NMR analysis. Compound 1 is a novel 21-membered Amphidinium macrolide, which contains one tetrahydrofuran ring, two ketone carbonyls, two hydroxyl groups, and six one-carbon branches. Compound 2 is a new 12-membered macrolide related to amphidinolide Q. Compound 1 exhibited cytotoxic activity against human cervix adenocarcinoma HeLa and murine hepatocellular carcinoma MH134 cells.

A study on the presence and relative abundance of benthic harmful algal bloom (BHAB) forming dinoflagellate species was carried out in the coral reefs of Sampadi Island, Sarawak, Malaysia. The study involved deployment of fiberglass screens as an artificial substrate for the benthic epiphytic microalgae. The screens were placed for 24 h above the seafloor along a 100 m transect at 10 m intervals. BHAB species attached to the screens were identified and cell abundances were enumerated under a light microscope. The BHAB community at the study site was dominated by Prorocentrum spp. and Coolia spp. Other BHAB species collected included Amphidinium spp., Gambierdiscus spp. and Ostreopsis spp. Total cell densities collected on the screens ranged from 5 to 100 cells per 100 cm2. The two BHAB groups of primary concern, Gambierdiscus spp. and Ostreopsis spp. were detected at relatively low abundances of 0.6–4.2% and 1.8–16% respectively. This study has shown that potentially toxic BHAB species were present in the coral reef and the artificial substrate approach could provide a convenient quantitative method for the collection of clean samples for identification and enumeration purposes.

A convergent synthesis of the C1–C13 segment of amphidinolide N, a potent cytotoxic marine macrolide isolated from the dinoflagellate Amphidinium sp., was achieved. The key features of the synthesis involve vinylogous Mukaiyama and Evans aldol reactions to form the C1–C7 and C8–C13 fragments, and convergent union of the two fragments by means of an aldol reaction to construct the C1–C13 segment.

A novel linear polyketide, amphirionin-2 ( 1 ), with two unique hexahydrofuro[3,2- b ]furan moieties has been isolated from the cultivated algal cells of a benthic dinoflagellate Amphidinium sp. (strain KCA09051). The structure was elucidated on the basis of detailed analyses of 2D NMR data, and the absolute configuration of C-5 was determined by using modified Mosher’s method. Amphirionin-2 ( 1 ) exhibited potent cytotoxic activity against human colon carcinoma Caco-2 cells and human lung adenocarcinoma A549 cells.

A new linear polyketide, amphidinin G (1), has been isolated from a symbiotic marine dinoflagellate Amphidinium sp. The planar structure of 1 was established mainly based on the 2D NMR data and the stereochemistry was elucidated by the combination of J-value analysis, modified Mosher’s method, and NMR chemical shift comparison with synthetic analogues. Amphidinin G (1) was expected to be a biosynthetic precursor of amphidinin A (2), a known linear dinoflagellate polyketide. Amphidinin G (1) showed antifungal activity against Trichophyton mentagrophytes.

The so-called unarmoured dinoflagellates are not a “natural” (phylogenetic) group but they lack thecal plates, share fragility and possess relatively few morphological characters that can be positively identified. This study depicts the species composition of unarmoured dinoflagellates collected from sites along the coasts of the Gulf of Mexico and the Mexican Pacific and includes their descriptions and illustrations. We identified a total of 25 species belonging to 13 genera and six families that were studied through various techniques using light and scanning electron microscopy. Seven new records for the Mexican Pacific are annotated here that include Amphidinium flagelans Schiller, Gyrodinium cochlea Lebour, G. glaebum Hulburt, G. metum Hulburt, Karenia selliformis Haywood, Steidinger et MacKenzie, Karlodinium ballantinum de Salas, and K. veneficum (Ballantine) Larsen. The genera Karenia and Karlodinium belong to the family Kareniaceae, characterised for encompassing the largest number of toxic species among the unarmoured dinoflagellates, and many species produce algal blooms around the world. Ceratoperidinium falcatum and Levanderina fissa are names recently proposed elsewhere as new taxonomic combinations and are also included here. The diversity of unarmoured dinoflagellates has been strongly underestimated in the past and the new records reported here confirm this. Further studies, including traditional and modern concepts and protocols (including molecular tools), should be undertaken in the near future to understand their real diversity.