DEVELOPMENT OF THE ENDOPARASITIC DINOFLAGELLATE AMOEBOPHRYA CERATII WITHIN HOST DINOFLAGELLATE SPECIES1

The endoparasitic dinoflagellate Amoebophrya ceratii Koeppen occurs in coastal waters of Nova Scotia within cells of two dinoflagellate hosts, a Scrippsiella species (probably S. trochoidea (Stein) Loeb. III) and Dino-physis norvegica Claparede & Lachman. We describe the development of the endoparasitic stage (the trophont) of A. ceratii within host cells using light and electron microscopy. After entry into the host, the trophont grows and expands until most of the host cell is occupied by the parasite. Growth is marked by a proliferation of trophont nuclei and flagella and by the formation of numerous lobes, each of which possesses a characteristic dinoflagellate amphiesma. The mature endoparasitic trophont is recognized at the light microscopic level as a beehive-shaped structure that consists of numerous lobes of the developing motile sporont cells and a mastigocoel cavity containing the sporont flagella.     

Observations on the mitosis and on the chromosome evolution during the lifecycle of Oodinium,a parasitic dinoflagellate

The life cycle of the dinoflagellate Oodinium alternates between an ectoparasitic trophic phase and a phase of multiplication as free-living flagellates. The nucleus of the young ectoparasite has rod-like chromosomes similar to those of free-living dinoflagellates. As growth of the trophont proceeds the nucleus becomes increasingly homogeneous. When Oodinium leaves its host, nuclear reorganization processes occur rapidly; they correspond to a peculiar prophase of the first sporogenetic division. The following division stages are similar. A conspicuous fusorial system appears between two archoplasmic areas which are responsible for daughter-chromosome segregation. The nuclear envelope remains intact while the fusorial microtubules are attached at distinct, kinetochore-like structures onto the nucleus. As the chromosomes become more condensed the kinetochore-like formations disappear.     

Terebrospira chattoni sp. n., a Parasite of the Endocuticle of the Shrimp Palaemonetes pugio Holthuis*

SYNOPSIS. Terebrospira chattoni sp. n. may be a species in transition between ectosymbiosis and endosymbiosis. It penetrates the epicuticle of Palaemonetes pugio and feeds on the endocuticle by dissolving galleries through it and absorbing the products of dissolution. Although similar in some respects to species of the endosymbiotic apostome genus Synophrya, T. chattoni is clearly related to ectosymbiotic apostomes that feed on exuvial fluid. However, instead of stimulating the metamorphosis of a phoront to a trophont, the host's ecdysis stimulates T. chattoni to metamorphose from a dedifferentiated trophont with 13 meridional kineties to a protomont, a predivision stage with 10 spiralled kineties. The protomont encysts and dedifferentiates to the division stage, an orthotomont with 13 kineties, either on the new exoskeleton before ecdysis, within a chamber in the endocuticle of the old exoskeleton, or on a substrate away from the host and the molt. The site of division determines the product of the division. On the new exoskeleton, the tomites in the reproductive cyst secrete walls around themselves thereby forming the lenticular, compartmented cysts characteristic of Terebrospira. Each daughter tunnels out of its compartment into the endocuticle. Although its infraciliature remains undifferentiated like that of the orthotomont, the ciliate in the gallery is the trophont, the only feeding stage in the life cycle. Daughters originating from the division of the orthotomont in a chamber in the endocuticle swim out of the exoskeleton at ecdysis. encyst on the substrate, and presumably form tomites. When the protomont itself leaves the molt, it encysts on the substrate and divides to form daughter cells with a rosette and the pattern of ciliature of the conventional tomite of other apostome genera. Tomites carry the infection to new hosts while compartmented cysts insure that the original host retains the infection. Terebrospira chattoni is always astomatous, although a dedifferentiated oral ciliature appears in the orthotomont and persists in the trophont. Terebrospira chattoni sp. n. is separated from T. lenticularis Debaisieux the other species in the genus because the latter species may divide outside a cyst and because T. chattoni has an extra reproductive stage in its life cycle.     

A NOVEL ASSOCIATION BETWEEN AN ENDEMIC STICKLEBACK AND A PARASITIC DINOFLAGELLATE. 2. MORPHOLOGY AND LIFE CYCLE1

An unusual dinoflagellate has been discovered in association with an endemic population of stickleback, Gasterosteus (L.), from the Queen Charlotte Islands, Canada. The dinoflagellate spends most of its life cycle as a coccoid vegetative cyst, not as a parasitic trophont. The vegetative cyst is unique in containing a rigid fenestrated matrix, which is penetrated by cytoplasmic process that emanate from a central area containing the dinokaryotic nucleus and associated chloroplasts. Some pores in the matrix are filled by oil droplets or starch granules. Intracellular bacteria are found throughout the cyst, sometimes in association with the nucleus. The cytoplasm contains accumulation bodes, microbodies, polyhedral crystals, chloroplasts and polyvesicular bodes. The encysted dinoflagellate has several potential strategies. It can 1) shed its wall and become amoeboid; 2) undergo sporogenesis and give rise to both regular and resistant spores; 3) divide mitotically, with a gradual reduction in the size of daughter cells down to 20 μm; and 4) apparently form a resting cyst, during which it secretes a thick outer wall composed of five layers. Taxonomically, this unusual dinoflagellate appears to be a new member of the Blastodiniales, although its position will become clearer when details of the motile stage are known.     

Revision of the family Duboscquellidae with description of Euduboscquella crenulata n. gen., n. sp. (Dinoflagellata, Syndinea), an intracellular parasite of the ciliate Favella panamensis Kofoid & Campbell

Recent recognition that tintinnids are infected by dinophycean as well as syndinean parasites prompts taxonomic revision of dinoflagellate species that parasitize these ciliates. Long overlooked features of the type species Duboscquella tintinnicola are used to emend the genus and family Duboscquellidae, resulting in both taxa being moved from the Syndinea to the Dinophyceae. Syndinean species previously classified as Duboscquella are relocated to Euduboscquella n. gen., with Euduboscquella crenulata n. sp. as the type. As an endoparasitic species, E. crenulata shares with its congeners processes associated with intracellular development and sporogenesis, but differs from closely related species in nuclear and cortical morphology of the trophont, including a distinctively grooved shield (= episome) that imparts a crenulated appearance in optical section. In addition, E. crenulata produces three morphologically distinct spore types, two of which undergo syngamy to form a uninucleate zygote. The zygote undergoes successive division to produce four daughter cells of unequal size, but that resemble the nonmating spore type.     

Duboscquella cachoni N. Sp., a Parasitic Dinoflagellate Lethal to Its Tintinnine Host Eutintinnus pectinis1

The parasitic dinoflagellate Duboscquella cachoni n. sp. is described from infestations of the tintinnine ciliate Eutintinnus pectinis collected from the Chesapeake Bay, a major North American estuary located on the east coast of the United States. Examination of parasite life history, morphology, and developmental processes reveals that D. cachoni differs from other members of the genus by the structure of the trophont, the pattern of sporogenesis, and spore morphology. Sporogenesis results in the production of either biflagellated macrospores, microspores with a single flagellum, or a cyst-like stage. The number of spores formed per infestation and their survival outside the host vary with spore type. Infested ciliates are apparently unable to reproduce, and infestations are always fatal to E. pectinis. Aspects of parasite biology and observations of a natural host-parasite assemblage suggest that D. cachoni may have a significant impact on its host's population dynamics.     

The Life Cycle and Morphology of the Apostomatous Ciliate,Hyalophysa chattoni n. g., n. sp.*

SYNOPSIS. A new apostome ciliate was discovered in collections at Friday Harbor, Washington and the San Francisco area. All stages of the life cycle were studied in both living and stained condition. Dormant encysted stages (phoronts) occur on the gills of Pagurus hirsutiusculus. Excystation occurs in synchrony with the molting of the host yielding the trophic stage (trophont), which feeds on the exuvial fluids trapped in the crab's cast-off exoskeleton. The trophont becomes greatly enlarged as a result of feeding, and the cytoplasm and organelles become compressed into a thin cortical layer. Each fully grown trophont encysts (becoming a tomont) as a prelude to repeated binary fission, which results in the release of actively motile offspring (tomites). These disperse and promptly resume the encysted phoront stage on the host's gills. The Chatton-Lwoff silver impregnation method revealed that all stages of the life cycle have nine somatic kineties. In the trophont stage they are accompanied by an anterior ventral field of scattered clumps of kinetosomes. During conjugation the partners attach by their ventral surfaces between kineties 1 and 9 and at the left of the ventral field. The tomite stage was stained with Protargol. In addition to the characteristic features of the foettingeriid tomite also revealed by the Chatton-Lwoff method, Protargol revealed the following heretofore undescribed morphological features: a short row of kinetosomes immediately anterior to the ogival field; a line paralleling the left margin of the field; the continuity of kinety 8 with falciform field 8; the entrance of kinety 9 into the mouth and its ending against the rosette (an enigmatic organelle characteristic of Foettingeriinae). Feulgen stains showed that the chromatin in the macronucleus is dispersed in aggregates whose size and number vary with the stage of the life cycle. The major period of chromatin synthesis appears to be during the early tomont stage, when Feulgen-positive material increases visibly in amount and intensity of staining. This apostome ciliate was characterized as a new genus on the basis of the infraciliature of the trophont stage, its conjugation with ventral surfaces appressed, and its life cycle. It is named Hyalophysa (hyalo = glassy, physa = bubble) chattoni.     

Characterization of the Parasitic Dinoflagellate Amoebophrya sp. Infecting Akashiwo sanguinea in Coastal Waters of China

The endoparasitic dinoflagellate Amoebophrya infects a number of free‐living marine dinoflagellates, including harmful algal bloom species. The parasitoid eventually kills its host and has been proposed to be a significant loss factor for dinoflagellate blooms in restricted coastal waters. For several decades, the difficulties of culturing host‐parasitoid systems have been a great obstacle for further research on the biology of Amoebophrya. Here, we established an Akashiwo sanguinea‐Amoebophrya sp. coculture from Chinese coastal waters and studied the parasitoid's generation time, dinospore survival and infectivity, as well as its host specificity. The lifespan of Amoebophrya sp. ex. A. sanguinea was approximately 58 h. The infective dinospores can survive up to 78 h in ambient waters but gradually lose their infectivity. The parasitoid was unable to infect other dinoflagellate species, its infection rate reached as high as 91% when the ratio of dinospores to host cells was 20:1. The high infectivity of dinospores suggests that the Amoebophrya strain was capable of removing a considerable fraction of host biomass within a short period, but that it is probably unable to maintain high infection levels under nonbloom conditions of its host, due to limited survival and time constraints in encountering host cells.     

Tintinnophagus acutus n. g., n. sp. (Phylum Dinoflagellata), an Ectoparasite of the Ciliate Tintinnopsis cylindrica Daday 1887, and Its Relationship to Duboscquodinium collini Grassé 1952

ABSTRACT. The dinoflagellate Tintinnophagus acutus n. g., n. sp., an ectoparasite of the ciliate Tintinnopsis cylindrica Daday, superficially resembles Duboscquodinium collini Grassé, a parasite of Eutintinnus fraknoii Daday. Dinospores of T. acutus are small transparent cells having a sharply pointed episome, conspicuous eyespot, posteriorly positioned nucleus with condensed chromosomes, and rigid form that may be supported by delicate thecal plates. Dinospores attach to the host via a feeding tube, losing their flagella, sulcus, and girdle to become spherical or ovoid cells. The trophont of T. acutus feeds on the host for several days, increasing dramatically in size before undergoing sporogenesis. Successive generations of daughter sporocytes are encompassed in an outer membrane or cyst wall, a feature not evident in trophonts. Tintinnophagus acutus differs from D. collini in host species, absence of a second membrane surrounding pre‐sporogenic stages, and failure to differentiate into a gonocyte and a trophocyte at the first sporogenic division. Phylogenetic analyses based on small subunit (SSU) ribosomal DNA (rDNA) sequences placed T. acutus and D. collini in the class Dinophyceae, with T. acutus aligned loosely with Pfiesteria piscicida and related species, including Amyloodinium ocellatum, a parasite of fish, and Paulsenella vonstoschii, a parasite of diatoms. Dubosquodinium collini nested in a clade composed of several Scrippsiella species and Peridinium polonicum. Tree construction using longer rDNA sequences (i.e. SSU through partial large subunit) strengthened the placement of T. acutus and D. collini within the Dinophyceae.     

The Fine Structure of Conidophrys pitelkae Bradbury Related to its Life Cycle and Taxonomic Position in the Apostomatida1

Electron microscopy of the tomite of Conidophrys pitelkae confirms that Jankowski was correct in including the pilisuctorians in the Apostomatida. Like other apostome tomites, the tomite of Conidophrys possesses a rosette opening to the exterior, kinetodesmata made up of stacks of individual kinetodesmal fibrils, and canaliculi that are surrounded by dense inclusion bodies and open on the ventral surface. The fine structure of the trophont of Conidophrys, however, is quite unlike that of other apostome trophonts. The elaborate infraciliature of the tomite disappears immediately after it settles and reappears de novo on the trophont just before tomitogenesis. The cyst wall, which completely encloses the trophont and grows with it, attaches the ciliate to a seta on its, host, the shrimp Crangon crangon. The setae on which tomites settle vary greatly in size and shape, but each appears to have at its tip some digitiform cuticular projections that surmount a pore, which opens into the lumen of the seta. The trophont's only direct connection to its host is at the cytostome, a unique structure formed of delicate tubules that pass through the pore into the lumen of the seta. Ingestion is by micropinocytosis, and there are no visible food reserves.     

Euduboscquella costata n. sp. (Dinoflagellata,Syndinea), an Intracellular Parasite of the Ciliate Schmidingerella arcuata: Morphology,Molecular Phylogeny,Life Cycle,Prevalence, and Infection Intensity

The syndinean dinoflagellate Euduboscquella costata n. sp., an intracellular parasite of the tintinnid ciliate Schmidingerella arcuata, was discovered from Korean coastal water in November of 2013. Euduboscquella costata parasitized in about 62% of the host population, with infection intensity (= number of trophonts in a single host cell) ranging from 1 to 8. Based on morphology and nuclear 18S ribosomal RNA gene sequences, the parasite is new to science. Euduboscquella costata n. sp. had an infection cycle typical of the genus, but had morphological and developmental features that distinguished it from congeneric species. These features include: (1) episome of the trophont with 25–40 grooves converging toward the center of the shield; (2) a narrow, funnel‐shaped lamina pharyngea extending from the margin of the episomal shield to the nucleus; (3) persistence of grooves during extracellular development (sporogenesis); (4) a single food vacuole during sporogenesis; (5) separation of sporocytes early in sporogenesis, regardless of type of spore formed; and (6) dinospore size (ca. 14 μm in length) and shape (bulbous episome with narrower, tapering hyposome). After sporogenesis, E. costata produced four different types of spore that showed completely identical 18S rRNA gene sequences. The gene sequence was completely identical with a previously reported population, Euduboscquella sp. ex S. arcuata, from Assawoman Bay, USA, indicating that the two populations are likely conspecific. Favella ehrenbergii, a widely recorded tintinnid known to host Euduboscquella spp., co‐occurred with S. arcuata, but was not infected by E. costata in field samples or during short‐term, cross‐infection experiments.     

Blastodinium galatheanum sp. nov. (Dinophyceae) a parasite of the planktonic copepod Acartia negligens (Crustacea,Calanoida) in the central Atlantic Ocean

A new dinoflagellate species, Blastodinium galatheanum sp. nov., was found parasitizing the planktonic copepods Acartia negligens and Acartia sp. in the Atlantic Ocean between the Azores and the Cape Verde Islands. These copepods have not previously been reported hosting a Blastodinium species. Characters that distinguish the new species are the shape and size of the trophic stage, its host species, and its predominantly solitary existence. Dinospores of Blastodinium galatheanum sp. nov. are peridinioid in nature and morphologically indistinguishable from dinospores of two other previously investigated Blastodinium species. SSU rRNA gene sequences from two isolates of this new species were almost identical and showed similarities to SSU rRNA sequences of other species of Blastodinium. A phylogenetic analysis based on SSU rRNA gene sequences suggested monophyly for all existing sequences of Blastodinium spp., including a sequence from the type species B. pruvoti, presented here for the first time.     

Phagotrophy and development ofPaulsenella cf.chaetoceratis (Dinophyta), an ectoparasite of the diatomStreptotheca thamesis

Zoospores of the dinophytePaulsenella cf.chaetoceratis, parasitizing the marine diatomStreptotheca thamesis, attach to the girdle region of the host and drive a peduncle into the cell interior. The peduncle consists of a non-cytoplasmic crook, a cytoplasmic feeding tube, and a presumably cellulosic sheath around the proximal part of the feeding tube. The crook seems to be used for attachment and penetration of the host. The mobile feeding tube induces shrinkage of the host vacuoles and takes up the complete host cytoplasm within less than 1 h. Phagocytosis depends on an intact host plasmalemma, which is not penetrated by the feeding tube. The trophic phase ends with retraction of the feeding tube. While the food is digested within a large vacuole, the trophont transforms into a thick-walled primary cyst. After about 12 h the primary cyst divides to form 3 or 4 secondary cysts. Finally, about 24 h after attacking the host, each secondary cyst releases two zoospores which may be again ready for infection within 1 h, without passing through any intermediate stage. The developmental times (above referred to 20 °C) are highly dependent on the temperature and can vary considerably, even between sister cells.Dedicated to Dr. Dr. h. c. P. Kornmann on his 75th birthday.     

Plagiodinium ballux sp. nov. (Dinophyceae), a deep (36 m) sand dwelling dinoflagellate from subtropical Japan

A new species of marine sand‐dwelling dinoflagellate, Plagiodinium ballux N. Yamada, Dawut, R. Terada & T. Horiguchi is described from a deep (36 m) seafloor off Takeshima Island, Kagoshima Prefecture, Japan in the subtropical region of the northwest Pacific. The species is thecate and superficially resembles species of Prorocentrum, but possesses an extremely small epitheca. The cell varies from ovoid to a rounded square, and is small (15.0–22.5 μm in length) and laterally compressed. The thecal plates are smooth and the thecal plate arrangement (Po, 1′, 0a, 5″, 5C, 2S, 5?, 0p, 1″″) is similar to that of Plagiodinium belizeanum, the type species of the genus. Molecular phylogenetic analyses based on SSU rDNA and partial LSU rDNA reveal that the dinoflagellate is closely related to P. belizeanum, but it can be clearly distinguished by its size and cell shape. This suite of morphological and molecular differences leads to the conclusion that this deep benthic dinoflagellate represents a new species of the genus Plagiodinium.     

Pyramidodinium atrofuscum gen. et sp. nov. (Dinophyceae), a new marine sand-dwelling coccoid dinoflagellate from tropical waters

A new marine sand‐dwelling coccoid dinoflagellate Pyramidodinium atrofuscum Horiguchi et Sukigara gen. et sp. nov. is described from Jellyfish Lake, Republic of Palau. The dinoflagellate alternates a non‐motile vegetative stage with a motile gymnodinioid stage within its life cycle. The non‐motile stage is dominant in the life cycle and the dinoflagellate reproduces itself by means of the production of two motile cells. The released motile cell swims only for a short period and is directly transformed into the non‐motile cell. The non‐motile cell is sessile, pyramidal in shape, with a single longitudinal ridge and a double transverse ridge. The surface of the cell wall is covered with many processes. The motile cell has a Gymnodinium‐like morphology, but no apical groove is present. An ultrastructural study revealed that the dinoflagellate possesses typical dinoflagellate organelles. Based on the unique morphology of the vegetative non‐motile stage, we propose a new genus Pyramidodinium for this dinoflagellate, with the type species Pyramidodinium atrofuscum Horiguchi et Sukigara, gen. et sp. nov.     

Occurrence of the Parasitic Dinoflagellate Amoebophrya ceratii in Chesapeake Bay Populations of Gymnodinium sanguineum

Chesapeake Bay populations of the red-tide dinoflagellate Gymnodinium sanguineum were regularly infected by the parasitic dinoflagellate Amoebophrya ceratii during the summers of 1988–1991. Infections developed inside the nucleus of G. sanguineum and were always lethal to the host. Parasite generation time was ? 40 h at 23° C, with the intracellular, trophont phase lasting 39.5 ± 0.3 h, and the extracellular, vermiform stage persisting for ? 20 min. Near surface accumulations of G. sanguineum sometimes exceeded 1,000 cells/ml; however, host abundance was relatively low when integrated over the surface mixed layer of each station (mean = 12.2 cells/ml ± 2.96 SE; n = 60). Parasitized hosts were encountered in 75% of the samples where host abundance was ≥ 1 per ml, and epidemic outbreaks (20–40% hosts infected) were observed on several occasions. Epidemic infections were generally located several meters below surface accumulations of G. sanguineum and were always restricted to a narrow region near the pycnocline. Consequently, integrated station values for parasite prevalence were low, with an average 2.7% (± 0.31 SE; n = 60). Parasite induced mortality removed up to 8% of G. sanguineum populations per day, but averaged < 2% of host biomass throughout the Bay. Thus, parasitism by A. ceratii does not appear to be a major factor regulating G. sanguineum bloom in the main stem of Chesapeake Bay.     

Gyrodinium undulans Hulburt, a marine dinoflagellate feeding on the bloom-forming diatomOdontella aurita, and on copepod and rotifer eggs

The marine dinoflagellateGyrodinium undulans was discovered as a feeder on the planktonic diatomOdontella aurita. Every year, during winter and early spring, a certain percentage of cells of this bloom-forming diatom, in the Wadden Sea along the North Sea coast, was regularly found affected by the flagellate. Supplied with the food diatomO. aurita the dinoflagellate could be maintained successfully in clonal culture. The vegetative life cylce was studied, mainly by light microscopy on live material, with special regard to the mode of food uptake. Food is taken up by a so-called phagopod, emerging from the antapex of the flagellate. Only fluid or tiny prey material could be transported through the phagopod. Larger organelles like the chloroplasts ofOdontella are not ingested and are left behind in the diatom cell. Thereafter, the detached dinoflagellate reproduces by cell division, occasionally followed by a second division. As yet, stages of sexual reproduction and possible formation of resting cysts could not be recognized, neither from wild material nor from laboratory cultures. Palmelloid stages (sometimes with a delicate wall) occurring in ageing cultures may at least partly function as temporary resting stages. The winter speciesG. undulans strongly resemblesSyltodinium listii, a summer species feeding on copepod and rotifer eggs. Surprisingly, in a few cases this prey material was accepted byG. undulans as well, at least under culture conditions. When fed with copepod eggs, the dinoflagellate developed into a large trophont, giving rise thereafter by repeated binary fission to 4, 8 or 16 flagellates, as a result of a single feeding act. A re-examination of both species under simultaneous culture conditions is planned.     

Susceptibility and tolerance of spotted seatrout, Cynoscion nebulosus , and red snapper, Lutjanus campechanus , to experimental infections with Amyloodinium ocellatum

Amyloodinium ocellatum is a parasitic dinoflagellate that infects warm-water marine and estuarine fishes and causes mortalities in aquaculture. Its life cycle consists of 3 stages: a feeding trophont that parasitizes the gills and skin where it interferes with gas exchange, osmoregulation, and tissue integrity; a detached reproductive tomont; and a free-swimming infective dinospore. We compared the susceptibility and tolerance of juvenile spotted seatrout, Cynoscion nebulosus, and red snapper, Lutjanus campechanus, to this parasite by individually exposing fish in 3-L aquaria (at 25 C and 33 practical salinity units) to several dinospore doses over different time periods and quantified the size and number of resulting trophonts. We estimated the trophont detachment rate and trophont size at detachment, the 24-hr dinospore infection rate, the dinospore 48-hr median lethal dose (LD(50)), and the trophont lethal load at the 48-hr LD(50). There were no significant differences in dinospore infection rates or dinospore lethal doses between spotted seatrout and red snapper; however, trophonts remained attached longer and attained a larger size in red snapper than in spotted seatrout. The trophont lethal load was significantly higher in spotted seatrout than in red snapper. A proposed model simulating the trophont dynamics reflected our experimental findings and showed that A. ocellatum reproductive success is linked both to the number of dinospores and the size of the trophont, factors that, in turn, are linked to the time the trophont spends on the host and the number of trophonts the host can tolerate.