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Gregarines are the most biodiverse group of apicomplexan parasites. This group specializes on invertebrate hosts (e.g., ascidians, crustaceans, and polychaetes). Marine gregarines are of particular interest because they are considered to be the earliest evolving apicomplexan lineage, having subsequently speciated (and radiated) through virtually all existing animal groups. Still, mechanisms governing the broad (global) distribution and speciation patterns of apicomplexans are not well understood. The present study examines Pacific lecudinids, one of the most species-rich and diverse groups of marine gregarines. Here, marine polychaetes were collected from intertidal zones. Single trophozoite cells were isolated for light and electron microscopy, as well as molecular phylogenetic analyses using the partial 18S rRNA gene. The cytochrome c oxidase subunit 1 gene was used to confirm morphology-based host identification. This study introduces Undularius glycerae n. gen., n. sp. and Lecudina kitase n. sp. (Hokkaido, Japan), as well as Difficilina fasoliformis n. sp. (California, USA). Occurrences of Lecudina cf. longissima and Lecudina cf. tuzetae (California, USA) are also reported. Phylogenetic analysis revealed a close relationship between L. pellucida , L. tuzetae , and L. kitase n. sp. Additionally, clustering among North Atlantic and Pacific L. tuzetae formed a species complex, likely influenced by biogeography. [ABSTRACT FROM AUTHOR]

Extreme functional reduction of mitochondria has taken place in parallel in many distantly related lineages of eukaryotes, leading to a number of recurring metabolic states with variously lost electron transport chain (ETC) complexes, loss of the tricarboxylic acid (TCA) cycle, and/or loss of the mitochondrial genome. The resulting mitochondria-related organelles (MROs) are generally structurally reduced and in the most extreme cases barely recognizable features of the cell with no role in energy metabolism whatsoever (e.g., mitosomes, which generally only make iron-sulfur clusters). Recently, a wide diversity of MROs were discovered to be hiding in plain sight: in gregarine apicomplexans. This diverse group of invertebrate parasites has been known and observed for centuries, but until recent applications of culture-free genomics, their mitochondria were unremarkable. The genomics, however, showed that mitochondrial function has reduced in parallel in multiple gregarine lineages to several different endpoints, including the most reduced mitosomes. Here we review this remarkable case of parallel evolution of MROs, and some of the interesting questions this work raises. [ABSTRACT FROM AUTHOR]

Marine gastrotrichs of the Pacific Ocean are poorly known. Here, we report on the finding of a marine chaetonotid gastrotrich of the genus Diuronotus from an intertidal beach within the Sea of Japan in Hokkaido (Japan). The Japanese individual shows a very close resemblance to Diuronotus aspetos. This new record is a consequential extension of its biogeographic range; previous records for representatives of this genus are confined to West Greenland, the North Sea and the east coast of North America. This rarely encountered, but seemingly widespread genus of marine gastrotrichs exemplifies our limited understanding of meiofaunal diversity and distribution patterns caused by sampling bias and insufficient knowledge on nominal species complexes. [ABSTRACT FROM AUTHOR]

This study describes a novel species of Haplozoon , H . ezoense n. sp., a dinoflagellate parasite isolated from the intestines of Praxillella pacifica (Polychaeta). Trophonts (feeding stages) of H . ezoense n. sp. were isolated and studied with scanning and transmission electron microscopy, and molecular phylogenetic analyses was performed using 18S rDNA and 28S rDNA. Trophonts had an average length of 120 μm, and were linear, forming a single longitudinal row comprising a trophocyte with a stylet, an average of 14 gonocytes (width = 10 μm), and bulbous cells that we concluded were likely sporocytes. The surface of H. ezoense n. sp. was covered with projections of the amphiesma. Sections viewed under TEM revealed multiple triple membrane-bound organelles reminiscent of relic non-photosynthetic plastids within the gonocytes. Haplozoon ezoense n. sp., H . praxillellae , and H. axiothellae formed a well-supported clade in the 18S rDNA datasets. The sequences of H . ezoense n. sp. differed from H . praxillellae , a species of Haplozoon isolated from the same host species in the Northeast Pacific, at 88/1,748 bases; and 155/1,752 bases from H . axiothellae . Concatenated 18S rDNA and 28S rDNA datasets were unable to resolve the deeper relationships of Haplozoon in the context of dinoflagellates. [ABSTRACT FROM AUTHOR]

Variations in toxicity of the benthic dinoflagellate Ostreopsis Schmidt 1901 have been attributed to specific molecular clades, biogeography of isolated strains, and the associated bacterial community. Here, we attempted to better understand the biodiversity and the basic biology influencing toxin production of Ostreopsis. Nine clonal cultures were established from Okinawa, Japan, and identified using phylogenetic analysis of the ITS-5.8S rRNA and 28S rRNA genes. Morphological analysis suggests that the apical pore complex L/W ratio could be a feature for differentiating Ostreopsis sp. 2 from the O. ovata species complex. We analyzed the toxicity and bacterial communities using liquid chromatography-mass spectrometry, and PCR-free metagenomic sequencing. Ovatoxin was detected in three of the seven strains of O. cf. ovata extracts , highlighting intraspecies variation in toxin production. Additionally, two new potential analogs of ovatoxin-a and ostreocin-A were identified. Commonly associated bacteria clades of Ostreopsis were identified from the established cultures. While some of these bacteria groups may be common to Ostreopsis (Rhodobacterales, Flavobacteria-Sphingobacteria, and Enterobacterales) , it was not clear from our analysis if any one or more of these plays a role in toxin biosynthesis. Further examination of biosynthetic pathways in metagenomic data and additional experiments isolating specific bacteria from Ostreopsis would aid these efforts. [ABSTRACT FROM AUTHOR]

Amphidiniopsis is a benthic, heterotrophic and thecate dinoflagellate genus that has a smaller epitheca and larger hypotheca. The genus contains 24 described species, but is considered to be polyphyletic based on morphological characters and molecular phylogenetics. In this study, two new species were discovered from two distant sampling localities, Amphidiniopsis crumena sp. nov. from Japan, and Amphidiniopsis nileribanjensis sp. nov., from Australia. These species have a uniquely shaped, additional second postcingular plate. Both species are dorsoventrally flattened, an apical hook is present, and have six postcingular plates. The plate formula is: APC 4′ 3a 7″ ?C 4?S 6″′ 2″″. The cells of these species were examined with LM and SEM, and molecular phylogenic analyses were performed using 18S and 28S rDNA. These species are distinguished by the presence of spines on the hypotheca and touching of the sixth postcingular plate and the anterior sulcal plate. Their shape and disposition of several thecal plates also differ. Molecular phylogenetic analyses showed that the two new species formed a monophyletic clade and did not belong to any morphogroup proposed by previous studies. Considering the morphological features and the molecular phylogenetic results, a new morphogroup is proposed, Amphidiniopsis morphogroup VI (' crumena group'). [ABSTRACT FROM AUTHOR]

The genus Amphidiniopsis is a benthic (sand-dwelling) lineage of thecate dinoflagellates, containing 19 morphologically diverse species. Past work has shown that some Amphidiniopsis species form a clade with the sand-dwelling Herdmania litoralis as well as some planktonic species in the family Protoperidiniaceae (i.e. the Monovela group). Still, our contemporary knowledge regarding Amphidiniopsis is limited, compared to the Protoperidiniaceae. To this end, we obtained 18S rDNA data from seven Amphidiniopsis species and a part of the 28S rDNA from four Amphidiniopsis species, with the goal of improving our understanding of phylogenetic relationships among Amphidiniopsis and the Monovela group. Results from the molecular phylogenetic analyses showed that Amphidiniopsis spp., with the exception of A. cf. arenaria , H. litoralis, and members within the Monovela group formed a single clade. Within the clade, relationships among Amphidiniopsis spp. and the Monovela group were more complicated — some subclades contained both representatives of Amphidiniopsis and the Monovela group. Our study suggests that habitat (benthic or planktonic), as well as traditionally used, general morphological characteristics, do not reflect molecular phylogenetic relationships, and that the taxonomy of the sand-dwelling genus Amphidiniopsis, and the planktonic family Protoperidiniaceae, should be reconsidered simultaneously. [ABSTRACT FROM AUTHOR]

Platyproteum is an enigmatic, monotypic genus formerly assigned to the Apicomplexa, until a recent phylogenomic study demonstrated that it diverged from the base of the chromerid/colpodellid (chrompodellid) taxa and apicomplexan clade. In the present study, a new species, P. noduliferae n. sp., is described using a combination of morphological and molecular data. Moreover, a reconstruction of the flagellar apparatus is presented to characterize the presence of flagella which was, until this study, an unknown trait for this genus. Phylogenetic analyses using rDNA sequences suggested that P. noduliferae n. sp. is a sister species of P. vivax , diverging from the base of chrompodellids and apicomplexans. This study provides new morphological data that corroborates the position of Platyproteum amongst other biflagellate species, contributing to an improved understanding of Platyproteum and the evolutionary changes undergone by some marine alveolates as they transitioned into obligate parasitic life styles. [ABSTRACT FROM AUTHOR]

Gregarine apicomplexans are a diverse group of single-celled parasites that have feeding stages (trophozoites) and gamonts that generally inhabit the extracellular spaces of invertebrate hosts living in marine, freshwater, and terrestrial environments. Inferences about the evolutionary morphology of gregarine apicomplexans are being incrementally refined by molecular phylogenetic data, which suggest that several traits associated with the feeding cells of gregarines arose by convergent evolution. The study reported here supports these inferences by showing how molecular data reveals traits that are phylogenetically misleading within the context of comparative morphology alone. We examined the ultrastructure and molecular phylogenetic positions of two gregarine species isolated from the spaghetti worm Thelepus japonicus : Selenidium terebellae Ray 1930 and S. melongena n. sp. The ultrastructural traits of S. terebellae were very similar to other species of Selenidium sensu stricto, such as having vermiform trophozoites with an apical complex, few epicytic folds, and a dense array of microtubules underlying the trilayered pellicle. By contrast, S. melongena n. sp. lacked a comparably discrete assembly of subpellicular microtubules, instead employing a system of fibrils beneath the cell surface that supported a relatively dense array of helically arranged epicytic folds. Molecular phylogenetic analyses of small subunit rDNA sequences derived from single-cell PCR unexpectedly demonstrated that these two gregarines are close sister species. The ultrastructural differences between these two species were consistent with the fact that S. terebellae infects the inner lining of the host intestines, and S. melongena n. sp. primarily inhabits the coelom, infecting the outside wall of the host intestine. Altogether, these data demonstrate a compelling case of niche partitioning and associated morphological divergence in marine gregarine apicomplexans. [ABSTRACT FROM AUTHOR]

This study examined the evolutionary history and diversity of marine gregarine parasites of pelagic zooplankton, and highlighted a unique example of a host-jumping event of cephaloidophorid gregarines between two distantly related host groups, crustaceans and chordates. Candacia bipinnata Giesbrecht, 1889, a free-living calanoid copepod, and a salp, Salpa fusiformis Cuvier, 1804, were collected on oceanic research cruises in 2018 and 2019, in the West Pacific aboard TRV SEISUI MARU and TOYOSHIO MARU, respectively. A molecular phylogeny based on 18S rDNA nested the gregarine parasite from S. fusiformis among cephaloidophorids, within a clade exclusively comprised of gregarines from crustaceans. The relationship between these groups was underpinned with ultrastructural data including the presence of a septum, and similarities in the apices of the epicytic folds. Subsequently, it was concluded to establish a new combination, Cephaloidophora cf. flava n. comb (Ex. Thalicola flava) and transfer the other two members of the Thalicola (also parasites of salps) to the Cephaloidophora. This study also attempted to ascertain the origin of cephaloidophorids in S. fusiformis. However, the relationship between Cephaloidophora bipinnatae n. sp., and C. cf. flava n. comb. had only modest support. [ABSTRACT FROM AUTHOR]

This study set out to bolster morphological and molecular datasets of marine gregarine apicomplexans. Gregarines were sampled from the Sea of Japan and Northwest Pacific from cirratuliform polychaetes (Acrocirridae, Cirratulidae, and Flabelligeridae), as well as sipunculids. Trophozoites (feeding stages) were gathered for identification using light microscopy, scanning electron microscopy, and transmission electron microscopy. Cells were also collected for molecular phylogenetic analysis using 18S rDNA and 28S rDNA. As a result, three new species of Selenidium , S. planusae n. sp., S. validusae n. sp., and S. pyroidea n. sp. were described, and additional morphological and genetic data were gathered for an existing species, S. orientale ; and Trollidium was established as a new genus. Trollidium akkeshiense n. gen. n. sp. possessed a unique, unsymmetrical organization of microtubules running the longitudinal length of one side of the trophozoite, corresponding to a zig-zag pattern of epicytic (surface) folds, and a flicking pattern of movement. Phylogenetic analyses of 18S rDNA and 28S rDNA showed that these portions of the ribosomal operon are able to resolve some relationships among Selenidium , while other lineages including Trollidium akkeshiense n. gen. n. sp. appeared to be highly influenced by long branch attraction. High evolutionary rates along the ribosomal operon of gregarines may hinder this marker from resolving deeper nodes among early apicomplexans. [ABSTRACT FROM AUTHOR]