Erythropsidinium (Gymnodiniales, Dinophyceae) in the Pacific Ocean, a unique dinoflagellate with an ocelloid and a piston

The distribution and morphology of the dinoflagellate Erythropsidinium (=Erythropsis) was studied in the vicinity of the Kuroshio and Oyashio Currents, the Philippine, Celebes, Sulu and South China Seas, western and central equatorial and southeast Pacific Ocean. Ninety-four specimens were observed, most of them collected from depths of less than 90m. The highest abundance (15cellsL(-1)) was recorded in the north Philippine Sea in May (32 degrees N, 138 degrees E, 30-m depth). Twenty-four specimens were found in a station in the offshore Perú-Chile Current (31 degrees 52'S, 91 degrees 24'W). The transition regions between open warm waters and productive currents or upwellings seem to favour the abundance of Erythropsidinium. Specimens with duplicate pistons, with two protuberant ocelloids, and specimens with a piston that attains up to 20 times the body length are illustrated for the first time. All the specimens have been ascribed to the type species, Erythropsidinium agile, until stable taxonomical criteria are established for the species diagnosis. Despite the complexity of its organelles, the ocelloid and piston, the competitiveness of Erythropsidinium in the pelagic ecosystem seems to be low.     

The function of the ocelloid and piston in the dinoflagellate Erythropsidinium (Gymnodiniales,Dinophyceae)

The marine dinoflagellate Erythropsidinium possesses an ocelloid, the most elaborate photoreceptor organelle known in a unicellular organism, and a piston, a fast contractile appendage unknown in any other organism. The ocelloid is able to rotate, often before the cell swims. The ocelloid contains lenses that function to concentrate light. The flagellar propulsion is atrophied, and the piston is responsible for locomotion through successive extensions and contractions. During the “locomotion mode”, the contraction is ~4 times faster than the extension. The piston attained up to 50 mm · s^?1 and the cell jumps backwards at ?4 mm · s^?1, while during the piston extension the cell moves forwards. The net speed of ~?1 mm · s^?1 is faster than other dinoflagellates. The piston usually moved in the “static mode” without significant cell swimming. This study suggests that the piston is also a tactile organelle that scans the surrounding waters for prey. Erythropsidinium feeds on copepod eggs by engulfing. The end of the piston possesses a “suction cup” able to attach the prey and place it into the posterior cavity for engulfing. The cylindrical shape of Erythropsidinium, and the anterior position of the ocelloid and nucleus, are morphological adaptations that leave space for the large vacuole. Observations are provided on morphological development during cell division. Most of the described species of Erythropsidinium apparently correspond to distinct life stages of known species, and the genus Greuetodinium (=Leucopsis) corresponds to an earlier division stage.     

Function and Evolutionary Origin of Unicellular Camera-Type Eye Structure

The ocelloid is an extraordinary eyespot organelle found only in the dinoflagellate family Warnowiaceae. It contains retina- and lens-like structures called the retinal body and the hyalosome. The ocelloid has been an evolutionary enigma because of its remarkable resemblance to the multicellular camera-type eye. To determine if the ocelloid is functionally photoreceptive, we investigated the warnowiid dinoflagellate Erythropsidinium. Here, we show that the morphology of the retinal body changed depending on different illumination conditions and the hyalosome manifests the refractile nature. Identifying a rhodopsin gene fragment in Erythropsidinium ESTs that is expressed in the retinal body by in situ hybridization, we also show that ocelloids are actually light sensitive photoreceptors. The rhodopsin gene identified is most closely related to bacterial rhodopsins. Taken together, we suggest that the ocelloid is an intracellular camera-type eye, which might be originated from endosymbiotic origin.     

Taxonomy and phylogeny of a new kleptoplastidal dinoflagellate, Gymnodinium myriopyrenoides sp. nov. (Gymnodiniales, Dinophyceae), and its cryptophyte symbiont

A new kleptoplastidal dinoflagellate, Gymnodinium myriopyrenoides sp. nov., was described using light microscopy, electron microscopy and phylogengetic analysis based on partial LSU rDNA sequences. Cells were dorsiventrally flattened, elongate-elliptical in ventral view. There was no displacement of the cingulum encircling the anterior part of the cell. The cingulum was curved posteriorly at the terminal junction with the sulcus. The sulcus was generally narrow but expanded in the posterior end. The epicone possessed an apical groove made of one and one-half counterclockwise revolutions. Phylogenetic analysis based on LSU rDNA showed that the sequence of G. myriopyrenoides was included in the Gymnodiniales sensu stricto clade and had special affinities with the species Amphidinium poecilochroum and Gymnodinium acidotum, which also harbor kleptochloroplasts. Phylogenetic analysis based on plastid-encoded SSU rDNA and ultrastructural observations suggested that the symbionts of G. myriopyrenoides were cryptophytes of the genus Chroomonas or Hemiselmis. Organelles including the nucleus, the nucleomorph, mitochondria, Golgi bodies and large chloroplasts remained in the cytoplasm of the symbionts, but not the periplast, ejectosomes or flagellar apparatus. The symbiotic level of G. myriopyrenoides was estimated to be a relatively early stage in the unarmored kleptoplastidal dinoflagellates.     

Studies on woloszynskioid dinoflagellates IV: The genus Biecheleria gen. nov.

The well known freshwater dinoflagellate Woloszynskia pseudopalustris is transferred to the new genus Biecheleria , based on the very unusual structure of the eyespot (comprising a stack of cisternae), the apical apparatus of a single elongate amphiesma vesicle, the structure of the resting cyst, and molecular data. Biecheleria is phylogenetically related to Symbiodinium and Polarella of the family Suessiaceae. This family, which extends back to the Jurassic, is redefined with the eyespot (Type E sensu Moestrup and Daugbjerg) and apical apparatus as diagnostic features, unknown elsewhere in the dinoflagellates. Biecheleria also comprises the brackish water species Biecheleria baltica sp. nov. (presently identified as Woloszynskia halophila ) and the marine species Biecheleria natalensis (syn. Gymnodinium natalense ). Gymnodinium halophilum described in 1952 by B. Biecheler but apparently not subsequently refound, is transferred to Biecheleria . The Suessiaceae further includes the marine species Protodinium simplex , described by Lohmann in 1908 but shortly afterwards (1921) transferred to Gymnodinium by Kofoid and Swezy and subsequently known as Gymnodinium simplex . It only distantly related to Gymnodinium . A new family, the Borghiellaceae, is proposed for the sister group to the Suessiaceae, based on eyespot structure (Type B of Moestrup and Daugbjerg), the morphology of the apical apparatus (if present), and molecular data. It presently comprises the genera Baldinia and Borghiella . Cells of Biecheleria pseudopalustris and B. baltica contain a microtubular strand (msp) associated with vesicles containing opaque material. Such structures are known in other dinoflagellates to serve as a peduncle, indicating that the two species may be mixotrophic.     

Surface ultrastructure and molecular phylogenetics of four unarmored heterotrophic dinoflagellates, including the type species of the genus Gyrodinium (Dinophyceae)

Small subunit rRNA gene sequences were determined for four unarmored heterotrophic dinoflagellates (Gyrodinium spirals, the type species of the genus Gyrodinium, as well as G. fusiforme, Gymnodinium rubrum and the freshwater species G. helveticum) using a single‐cell polymerase chain reaction (PCR) technique. For identification and record keeping, each cell was carefully observed and photographed using a light microscope under high magnification, prior to single‐cell PCR. G. rubrum and G. helveticum possess an elliptical apical groove and longitudinal striations similar to those of G. spirale and G. fusiforme, and molecular phylogenetic studies reveal that the four species form a single clade. We therefore propose the following new combinations: Gyrodinium rubrum (Kofoid et Swezy) Takano et Horiguchi comb. nov. and Gyrodinium helveticum (Penard) Takano et Horiguchi comb. nov.     

Molecular phylogeny of ocelloid-bearing dinoflagellates (Warnowiaceae) as inferred from SSU and LSU rDNA sequences

Background  

Dinoflagellates represent a major lineage of unicellular eukaryotes with unparalleled diversity and complexity in morphological features. The monophyly of dinoflagellates has been convincingly demonstrated, but the interrelationships among dinoflagellate lineages still remain largely unresolved. Warnowiid dinoflagellates are among the most remarkable eukaryotes known because of their possession of highly elaborate ultrastructural systems: pistons, nematocysts, and ocelloids. Complex organelles like these are evolutionary innovations found only in a few athecate dinoflagellates. Moreover, the taxonomy of warnowiids is extremely confusing and inferences about the evolutionary history of this lineage are mired by the absence of molecular phylogenetic data from any member of the group. In this study, we provide the first molecular phylogenetic data for warnowiids and couple them with a review of warnowiid morphological features in order to formulate a hypothetical framework for understanding character evolution within the group. These data also enabled us to evaluate the evolutionary relationship(s) between warnowiids and the other group of dinoflagellates with complex organelles: polykrikoids.     

Large-subunit ribosomal RNA systematics of symbiotic dinoflagellates: morphology does not recapitulate phylogeny

Biochemical, histological, physiological, and genetic evidence indicates that dinoflagellates symbiotic with marine invertebrates are a heterogeneous complex of taxa, representing at least five genera in three orders. Despite a wealth of data regarding morphological, biochemical, and behavioral differences among symbiotic dinoflagellates, knowledge concerning patterns of diversification is limited. I analyzed approximately 900 bp of the 5' end of the large-subunit ribosomal RNA gene from 14 dinoflagellate isolates: six cultured Symbiodinium specimens, two cultured symbiotic Gymnodinium, two algal samples isolated from reef-building corals, an algal sample obtained from cultures of the jellyfish Cassiopea xamachana, and three free-living Gymnodinium isolates. Results show that morphological similarities among the examined symbiotic taxa do not necessarily correspond with molecular phylogeny. The included Symbiodinium taxa represent a paraphyletic assemblage while Gymnodinium is reconstructed as a polyphyletic assemblage. Analysis indicates that all the included symbiotic dinoflagellates descended from a common, symbiotic ancestor (though within the dinoflagellates, symbiosis is a polyphyletic trait). Additionally, two free-living dinoflagellates emerge within the symbiotic clade, suggesting that the symbiotic lifestyle has been lost at least once in this group. It has been hypothesized that rates of evolution within mutualistic endosymbioses should be reduced relative to free-living taxa. However, results indicate that rates of molecular, morphological, biochemical and behavioral change are similar among branches leading to symbiotic and free-living dinoflagellates.     

ULTRASTRUCTURE OF GYMNODINIUM AUREOLUM (DINOPHYCEAE): TOWARD A FURTHER REDEFINITION OF GYMNODINIUM SENSU STRICTO

Examination of the ultrastucture of the unarmored dinoflagellate Gymnodinium aureolum (Hulburt) G. Hansen (syn: Gyrodinium aureolum Hulburt) revealed the presence of nuclear chambers, which are specialized differentiations of the nuclear envelope, similar to those described in the type species of Gymnodinium , G. fuscum (Ehrenberg) Stein and certain other Gymnodinium species. The nuclear pores were restricted to these chambers. In the flagellar apparatus a nuclear fibrous connective linked the longitudinal microtubular root and the nucleus. This structure had so far been observed only in Gymnodinium spp. and in the heterotrophic species Actiniscus pentasterias (Ehrenberg) Ehrenberg, Nematodinium armatum (Dogiel) Kofoid et Swezy and Polykrikos kofoidii Chatton. Another unusual feature of G. aureolum was the presence of a striated fiber in the longitudinal flagellum, a feature previously only found in Ceratium furca (Ehrenberg) Claparède et Lachmann and C. tripos (O.F. Müller) Nitzsch. Gymnodinium aureolum also possessed a prominent ventral protrusion associated with the peduncle and containing electron opaque material. It is concluded that G. aureolum belongs to the Gymnodinium sensu stricto group. This may be a temporary classification, however, because G. aureolum and its allies differ from the type species G. fuscum by the presence of a transverse striated root, striated collars, trichocysts, and a peduncle.     

Piscinoodinium, a fish-ectoparasitic dinoflagellate, is a member of the class dinophyceae, subclass gymnodiniphycidae: convergent evolution with Amyloodinium

All dinoflagellates that infest the skin and gills of fish have traditionally been placed within the class Blastodiniphyceae. Their relatedness was primarily based upon a similar mode of attachment to the host, i.e., attachment disc with holdfasts. Results of recent molecular genetic analyses have transferred these parasites, including Amyloodinium, to the class Dinophyceae, subclass Peridiniphycidae. In our study, a small subunit rDNA gene from a parasitic dinoflagellate that has features diagnostic for species in the genus Piscinoodinium, i.e., typical trophont with attachment disc having rhizocysts, infesting the skin of freshwater tropical fish, places this organism within the dinophycean subclass Gymnodiniphycidae. This suggests a close relationship of Piscinoodinium spp. to dinoflagellates that include symbionts, e.g., species of Symbiodinium, and free-living algae, e.g., Gymnodinium spp. These molecular and morphological data suggest that evolution of this mode of fish ectoparasitism occurred independently in 2 distantly related groups of dinoflagellates, and they further suggest that the taxonomic status of parasites grouped as members of Piscinoodinium requires major revision.     

THE UNIQUE,MICRORETICULATE CYST OF THE NAKED DINOFLAGELLATE GYMNODINIUM CATENATUM1

Gymnodinium catenatum Graham is an unarmored dinoflagellate responsible for episodes of paralytic shellfish poisoning. This species forms a resting cyst that is unique in several ways. The outer surface of the spherical, brownish cyst is microreticulate and composed of hundreds of 1-3 μm polygons. In several regions, these polygons are smaller, more uniform in shape, and oriented in distinct bands that define morphological features. These features on the cyst reflect the cingulum, sulcus, flagellar pore complex, and acrobase of the motile stage precursor to the cyst. The archeopyle is irregularly but extensively developed. Its margin is generally smooth and extends almost completely around the circumference of the cyst, though not consistently in the plane of the equator. The cyst wall is resistant to acetolysis and standard palynological preparation techniques. Gymnodinium catenatum Graham is emended to include the details of the cyst stage. The significance of this cyst is that it is the first described cyst of a naked dinoflagellate that bears oriented surface ornamentation reflecting features of the motile dinoflagellate. Its microreticulate surface ornamentation is unique to dinocysts, naked or armored, living or fossilized. Resistance of the cyst wall to harsh processing techniques suggests the presence of sporopollenin-like material commonly associated with cysts of armored dinoflagellates. From an ecological standpoint, the existence of a G. catenatum cyst has important implications with respect to species bloom dynamics and geographic distribution. In addition, the distinct differences between this cyst and those of the armored saxitoxin-producing gonyaulacoid species argues against a proposed evolutionary linkage.     

Phylogenetic study of Gymnodinium dorsalisulcum comb. nov. from tropical Australian coastal waters (Dinophyceae)

A new species of the dinoflagellate genus Gymnodinium Stein, previously considered a member of Katodinium Fott, is characterized from two marine benthic habitats in tropical northern Australia. Gymnodinium dorsalisulcum comb. nov. was found to be very abundant at times, and in culture produced large quantities of mucus. We analyzed two regions of ribosomal DNA from this species (partial large subunit and complete small subunit sequences), using Bayesian analysis and phylogenetic models appropriate to alignments of ribosomal RNA genes. We compared it to eight species of the ‘true’Gymnodinium clade and to other dinoflagellates. The results show that it is a member of the Gymnodinium clade, and is closely related to Gymnodinium impudicum and G. chlorophorum. Katodinium was originally defined as having cells with an epitheca that is much larger than the hypotheca. However, this character is clearly inadequate, and the genus requires a re‐investigation to determine the apomorphies of the type species.     

Comparative Toxicity of Gonyaulax monilata and Gymnodinium breve to Annelids, Crustaceans, Molluscs and a Fish

SYNOPSIS. Toxicities of laboratory cultures of the dinoflagellates Gonyaulax monilata and Gymnodinium breve were compared using fish, annelids, crustaceans and molluscs. Toxicity was evaluated as mortality over a 48-hr test period in 100%, 75% 50%, 25% and 10% concentrations of dinoflagellate cultures. Responses of the assay animals indicated that the dinoflagellates do not produce the same toxins. Effects of the toxins seemed uniform within each major group of animals tested. Fish were most sensitive to both G. breve and Gonyaulax monilata; crustaceans were resistant to both; annelids and molluscs were more sensitive to G. monilata than to G. breve.     

Phylogenetic analyses indicate that the 19'Hexanoyloxy-fucoxanthin-containing dinoflagellates have tertiary plastids of haptophyte origin

The three anomalously pigmented dinoflagellates Gymnodinium galatheanum, Gyrodinium aureolum, and Gymnodinium breve have plastids possessing 19'-hexanoyloxy-fucoxanthin as the major carotenoid rather than peridinin, which is characteristic of the majority of the dinoflagellates. Analyses of SSU rDNA from the plastid and the nuclear genome of these dinoflagellate species indicate that they have acquired their plastids via endosymbiosis of a haptophyte. The dinoflagellate plastid sequences appear to have undergone rapid sequence evolution, and there is considerable divergence between the three species. However, distance, parsimony, and maximum-likelihood phylogenetic analyses of plastid SSU rRNA gene sequences place the three species within the haptophyte clade. Pavlova gyrans is the most basal branching haptophyte and is the outgroup to a clade comprising the dinoflagellate sequences and those of other haptophytes. The haptophytes themselves are thought to have plastids of a secondary origin; hence, these dinoflagellates appear to have tertiary plastids. Both molecular and morphological data divide the plastids into two groups, where G. aureolum and G. breve have similar plastid morphology and G. galatheanum has plastids with distinctive features.     

Gymnodinium chukwanii n. sp. and Other Marine Dinoflagellates Collected in the Vicinity of Zanzibar

Thirty-five species of marine dinoflagellates are described and figured, including one new species, Gymnodinium chukwanii . These were collected by the author during the period February - March 1956. G. chukwanii has affinities to G. splendens and G. nelsoni and their group. The remainder of the paper is concerned with described species.     

Multiple strains of the parasitic dinoflagellate Amoebophrya exist in Chesapeake Bay

Small subunit rRNA sequences were amplified from Amoebophrya strains infecting Karlodinium micrum, Gymnodinium instriatum and an unidentified Scrippsiella species in Chesapeake Bay. The alignable parts of the sequences differed from each other and from the previously reported rRNA sequence of the Amoebophrya strain infecting Akashiwo sanguinea in Chesapeake Bay by 4 to 10%. This is a greater degree of difference than sometimes found between sequences from separate genera of free-living dinoflagellates. These sequence differences indicate that the Amoebophrya strains parasitizing dinoflagellates in Chesapeake Bay do not all belong to the same species. In spite of their relative dissimilarity, the sequences do group together into a single clade with high bootstrap support in phylogenetic trees constructed from the sequences.     

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).     

ULTRASTRUCTURE OF THE RED TIDE DINOFLAGELLATE GYMNODINIUM BREVE. I. GENERAL DESCRIPTION1,2,3

Gymnodimium breve Davis, an unarmored marine dinoflagellate has a cell covering (theca) composed of four membranes. The inner two membranes represent a vesicular layer and in tangential section, the theca appears composed of polygonal areas. Unusual threat ridges are located in the cingular region between the epi- and hypocone. This osmotically sensitive species is extremely vesiculate with dispersed areas of cytoplasm containing typical eukaryotic organelles as well as other organelles found only in dinoflagellates. The non-vesiculated cytoplasm is continuous in serial sections. The chloroplasts can contain either quasi-radial or parallel lamellae typically consisting of three thylakoids each. The pyrenoid is multiple-stalked and lacks a starch cap. The dinophycean pusule is simple and similar to those found in several unarmored marine species. The nucleus is typically dinophycean but the chromosomes appear to lack nonfibrillar material.     

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.