Search

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier GmbH. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier GmbH.. All rights reserved.)

Microturbellarians are abundant and ubiquitous members of marine meiofaunal communities around the world. Because of their small body size, these microscopic animals are rarely considered as hosts for parasitic organisms. Indeed, many protists, both free-living and parasitic ones, equal or surpass meiofaunal animals in size. Despite several anecdotal records of "gregarines", "sporozoans", and "apicomplexans" parasitizing microturbellarians in the literature-some of them dating back to the nineteenth century-these single-celled parasites have never been identified and characterized. More recently, the sequencing of eukaryotic microbiomes in microscopic invertebrates have revealed a hidden diversity of protist parasites infecting microturbellarians and other meiofaunal animals. Here we show that apicomplexans isolated from twelve taxonomically diverse rhabdocoel taxa and one species of proseriate collected in four geographically distinct areas around the Pacific Ocean (Okinawa, Hokkaido, and British Columbia) and the Caribbean Sea (Curaçao) all belong to the apicomplexan genus Rhytidocystis. Based on comprehensive molecular phylogenies of Rhabdocoela and Proseriata inferred from both 18S and 28S rDNA sequences, as well as a molecular phylogeny of Marosporida inferred from 18S rDNA sequences, we determine the phylogenetic positions of the microturbellarian hosts and their parasites. Multiple lines of evidence, including morphological and molecular data, show that at least nine new species of Rhytidocystis infect the microturbellarian hosts collected in this study, more than doubling the number of previously recognized species of Rhytidocystis, all of which infect polychaete hosts. A cophylogenetic analysis examining patterns of phylosymbiosis between hosts and parasites suggests a complex picture of overall incongruence between host and parasite phylogenies, and varying degrees of geographic signals and taxon specificity., (© 2023. The Author(s).)

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., (Copyright © 2022 Elsevier GmbH. All rights reserved.)

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier GmbH. All rights reserved.)

Apicomplexa (sensu stricto) are a diverse group of obligate parasites to a variety of animal species. Gregarines have been the subject of particular interest due to their diversity, phylogenetically basal position, and more recently, their symbiotic relationships with their hosts. In the present study, four new species of marine eugregarines infecting ascidian hosts (Lankesteria kaiteriteriensis sp. nov., L. dolabra sp. nov., L. savignyii sp. nov., and L. pollywoga sp. nov.) were described using a combination of morphological and molecular data. Phylogenetic analysis using small subunit rDNA sequences suggested that gregarines that parasitize ascidians and polychaetes share a common origin as traditionally hypothesized by predecessors in the discipline. However, Lankesteria and Lecudina species did not form clades as expected, but were instead intermixed amongst each other and their respective type species in the phylogeny. These two major genera are therefore taxonomically problematic. We hypothesize that the continued addition of new species from polychaete and tunicate hosts as well as the construction of multigene phylogenies that include type-material will further dissolve the currently accepted distinction between Lankesteria and Lecudina. The species discovered and described in the current study add new phylogenetic and taxonomic data to the knowledge of marine gregarine parasitism in ascidian hosts., (Copyright © 2021. Published by Elsevier Inc.)

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., (Copyright © 2019 Elsevier GmbH. All rights reserved.)

Described here is a polymerase chain reaction (PCR) test to detect the apicomplexan-X (APX) parasite of a flat oyster species, Ostrea chilensis, endemic to New Zealand. The test primers target sequences in the in situ hybridisation probes identified to bind specifically to APX 18S rRNA and amplify a 723 bp DNA product. The test did not amplify 18S rRNA gene sequences of other apicomplexan species, including Toxoplasma gondii, Neospora caninum, Selenidium spp., Cephaloidophorida spp., Lecudina spp. and Thiriotia sp. Of 73 flat oysters identified by histology to be infected with APX at different severities, 69 (95%) tested PCR-positive. Failure to amplify an internal control indicated the presence of PCR inhibitors in the 4 PCR-negative samples. The high analytical sensitivity, specificity and speed of the PCR test should make it a useful tool for detecting APX.

Marine gregarines are unicellular parasites of invertebrates commonly found infecting the intestine and coelomic spaces of their hosts. Situated at the base of the apicomplexan tree, marine gregarines offer an opportunity to explore the earliest stages of apicomplexan evolution. Classification of marine gregarines is often based on the morphological traits of the conspicuous feeding stages (trophozoites) in combination with host affiliation and molecular phylogenetic data. Morphological characters of other life stages such as the spore are also used to inform taxonomy when such stages can be found. The reconstruction of gregarine evolutionary history is challenging, due to high levels of intraspecific variation of morphological characters combined with relatively few traits that are taxonomically unambiguous. The current study combined morphological data with a phylogenetic analysis of small subunit rDNA sequences to describe and establish a new genus and species (Cuspisella ishikariensis n. gen., n. sp.) of marine gregarine isolated from the intestine of a polynoid host (Lepidonotus helotypus) collected from Hokkaido, Japan. This new species possesses a set of unusual morphological traits including a spiked attachment apparatus and sits on a long branch on the molecular phylogeny. Furthermore, this study establishes a molecular phylogenetic position for Loxomorpha cf. harmothoe, a previously described marine gregarine, and reveals a new group of gregarines that infect polynoid hosts., (© 2018 The Author(s) Journal of Eukaryotic Microbiology © 2018 International Society of Protistologists.)

In an effort to broaden our understanding of the biodiversity and distribution of gregarines infecting crustaceans, this study describes two new species of gregarines, Thiriotia hyperdolphinae n. sp. and Cephaloidophora oradareae n. sp., parasitizing a deep sea amphipod (Oradarea sp.). Amphipods were collected using the ROV Hyper-Dolphin at a depth of 855 m while on a cruise in Sagami Bay, Japan. Gregarine trophozoites and gamonts were isolated from the gut of the amphipod and studied with light and scanning electron microscopy, and phylogenetic analysis of 18S rDNA. Thiriotia hyperdolphinae n. sp. was distinguished from existing species based on morphology, phylogenetic position, as well as host niche and geographic locality. Cephaloidophora oradareae n. sp. distinguished itself from existing Cephaloidophora, based on a difference in host (Oradarea sp.), geographic location, and to a certain extent morphology. We established this latter new species with the understanding that a more comprehensive examination of diversity at the molecular level is necessary within Cephaloidophora. Results from the 18S rDNA molecular phylogeny showed that T. hyperdolphinae n. sp. was positioned within a clade consisting of Thiriotia spp., while C. oradareae n. sp. grouped within the Cephaloidophoridae. Still, supplemental genetic information from gregarines infecting crustaceans will be needed to better understand relationships within this group of apicomplexans., (© 2017 The Author(s) Journal of Eukaryotic Microbiology © 2017 International Society of Protistologists.)

Gregarine apicomplexans are unicellular parasites commonly found in the intestines and coeloms of invertebrate hosts. Traits associated with the conspicuous feeding stage of gregarines, known as the trophozoite, have been used in combination with molecular phylogenetic data for species delimitation and the reconstruction of evolutionary history. Trophozoite morphology alone is often inadequate for inferring phylogenetic relationships and delimiting species due to frequent cases of high intraspecific variation combined with relatively low interspecific variation. The current study combined morphological data with small subunit (SSU) rDNA sequences to describe and establish two novel marine gregarine species isolated from the intestine of a polychaete host Lumbrineris inflata collected in British Columbia (Canada): Paralecudina anankea n. sp. and Lecudina caspera n. sp. The sister species to the host is Lumbrineris japonica, which can be found on the opposite side of the Pacific Ocean (Japan) and contains two different species of gregarine parasites: Paralecudina polymorpha and Lecudina longissima. Molecular phylogenetic analyses placed P. anankea n. sp. as the sister species to P. polymorpha and L. caspera n. sp. as the sister species to L. longissima. This phylogenetic pattern demonstrates a co-evolutionary history whereby speciation of the host (Lumbrineris) corresponds with simultaneous speciation of the two different lineages of intestinal gregarines (Paralecudina and Lecudina)., (© 2017 The Author(s) Journal of Eukaryotic Microbiology © 2017 International Society of Protistologists.)

Apicomplexa is a large phylum of parasitic protists renowned for significant negative health impacts on humans and livestock worldwide. Despite the prevalence and negative impacts of apicomplexans across many animal groups, relatively little attention has been given to apicomplexan parasites of invertebrates, especially marine invertebrates. Previous work has reported an apicomplexan parasite 'X' (APX), a parasite that has been histologically and ultrastructurally identified from the commercially important flat oyster Ostrea chilensis in New Zealand. This apicomplexan may exacerbate host vulnerability to the infectious disease bonamiosis. In this study, we report 18S rRNA sequences amplified from APX-infected O. chilensis tissues. Phylogenetic analyses clearly established that the 18S sequences were of apicomplexan origin; however, their detailed relationship to known apicomplexan groups is less resolved. Two specific probes, designed from the putative APX 18S rRNA sequence, co-localised with APX cells in in situ hybridisations, further supporting our hypothesis that the 18S sequences were from APX. These sequences will facilitate the future development of inexpensive and sensitive molecular diagnostic tests for APX, thereby assisting research focussed on the biology and ecology of this organism and its role in morbidity and mortality of O. chilensis.

A novel species of aseptate eugregarine, Ganymedes yurii sp. n., is described using microscopic and molecular approaches. It inhabits the intestine of Gondogeneia sp., a benthic amphipod found along the shore of James Ross Island, Weddell Sea, Antarctica. The prevalence of the infection was very low and only a few caudo-frontal syzygies were found. Morphologically, the new species is close to a previously described amphipod gregarine, Ganymedes themistos, albeit with several dissimilarities in the structure of the contact zone between syzygy partners, as well as other characteristics. Phylogenetic analysis of the 18S rDNA from G. yurii supported a close relationship between these species. These two species were grouped with other gregarines isolated from crustaceans hosts (Cephaloidophoroidea); however, statistical support throughout the clade of Cephaloidophoroidea gregarines was minimal using the available dataset., (© 2016 The Author(s) Journal of Eukaryotic Microbiology © 2016 International Society of Protistologists.)

The eugregarines are a group of apicomplexan parasites that mostly infect the intestines of invertebrates. The high level of morphological variation found within and among species of eugregarines makes it difficult to find consistent and reliable traits that unite even closely related lineages. Based mostly on traits observed with light microscopy, the majority of described eugregarines from marine invertebrates has been classified into a single group, the Lecudinidae. Our understanding of the overall diversity and phylogenetic relationships of lecudinids is very poor, mainly because only a modest amount of exploratory research has been done on the group and very few species of lecudinids have been characterized at the molecular phylogenetic level. In an attempt to understand the diversity of marine gregarines better, we surveyed lecudinids that infect the intestines of Pacific ascidians (i.e. sea squirts) using ultrastructural and molecular phylogenetic approaches; currently, these species fall within one genus, Lankesteria. We collected lecudinid gregarines from six ascidian host species, and our data demonstrated that each host was infected by a different species of Lankesteria: (i) Lankesteria hesperidiiformis sp. nov., isolated from Distaplia occidentalis, (ii) Lankesteria metandrocarpae sp. nov., isolated from Metandrocarpa taylori, (iii) Lankesteria halocynthiae sp. nov., isolated from Halocynthia aurantium, (iv) Lankesteria herdmaniae sp. nov., isolated from Herdmania momus, (v) Lankesteria cf. ritterellae, isolated from Ritterella rubra, and (vi) Lankesteria didemni sp. nov., isolated from Didemnum vexillum. Visualization of the trophozoites with scanning electron microscopy showed that four of these species were covered with epicytic folds, whereas two of the species were covered with a dense pattern of epicytic knobs. The molecular phylogenetic data suggested that species of Lankesteria with surface knobs form a clade that is nested within a paraphyletic assemblage species of Lankesteria with epicytic folds.

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 terebellaeRay 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., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

Gregarines are a diverse group of apicomplexan parasites with a conspicuous extracellular feeding stage, called a "trophozoite", that infects the intestines and other body cavities of invertebrate hosts. Although the morphology of trophozoites is very diverse in gregarines as a whole, high degrees of intraspecific variation combined with relatively low degrees of interspecific variation make the delimitation of different species based on trophozoite morphology observed with light microscopy difficult. The coupling of molecular phylogenetic data with comparative morphology has shed considerable light onto the boundaries and interrelationships of different gregarine species. In this study, we isolated a novel marine gregarine from the hepatic region of a Pacific representative of the hemichordate Glossobalanus minutus, and report the first ultrastructural and molecular data from any gregarine infecting this distinctive group of hosts. Molecular phylogenetic analyses of an SSU rDNA sequence derived from two single-cell isolates of this marine gregarine demonstrated a strong and unexpected affiliation with a clade of terrestrial gregarines (e.g. Gregarina). This molecular phylogenetic data combined with a comparison of the morphological features in previous reports of gregarines collected from Atlantic representatives of G. minutus justified the establishment of a new binomial for the new isolate, namely Caliculium glossobalani n. gen. et sp. The molecular phylogenetic analyses demonstrated a clade of terrestrial gregarines associated with a sequence acquired from a marine species, which suggest that different groups of terrestrial/freshwater gregarines evolved independently from marine ancestors., (© 2014 The Author(s) Journal of Eukaryotic Microbiology © 2014 International Society of Protistologists.)

Selenidium is a genus of gregarine parasites that infect the intestines of marine invertebrates and have morphological, ecological, and motility traits inferred to reflect the early evolutionary history of apicomplexans. Because the overall diversity and phylogenetic position(s) of these species remain poorly understood, we performed a species discovery survey of Selenidium from tube-forming polychaetes. This survey uncovered five different morphotypes of trophozoites (feeding stages) living within the intestines of three different polychaete hosts. We acquired small subunit (SSU) rDNA sequences from single-cell (trophozoite) isolates, representing all five morphotypes that were also imaged with light and scanning electron microscopy. The combination of molecular, ecological, and morphological data provided evidence for four novel species of Selenidium, two of which were established in this study: Selenidium neosabellariae n. sp. and Selenidium sensimae n. sp. The trophozoites of these species differed from one another in the overall shape of the cell, the specific shape of the posterior end, the number and form of longitudinal striations, the presence/absence of transverse striations, and the position and shape of the nucleus. A fifth morphotype of Selenidium, isolated from the tube worm Dodecaceria concharum, was inferred to have been previously described as Selenidium cf. echinatum, based on general trophozoite morphology and host association. Phylogenetic analyses of the SSU rDNA sequences resulted in a robust clade of Selenidium species collected from tube-forming polychaetes, consisting of the two new species, the two additional morphotypes, S. cf. echinatum, and four previously described species (Selenidium serpulae, Selenidium boccardiellae, Selenidium idanthyrsae, and Selenidium cf. mesnili). Genetic distances between the SSU rDNA sequences in this clade distinguished closely related and potential cryptic species of Selenidium that were otherwise very similar in trophozoite morphology., (© 2013 The Author(s) Journal of Eukaryotic Microbiology © 2013 International Society of Protistologists.)

Marine gregarines are poorly understood apicomplexan parasites with large trophozoites that inhabit the body cavities of marine invertebrates. Two novel species of gregarines were discovered in polychaete hosts collected in Canada and Japan. The trophozoites of Trichotokara japonica n. sp. were oval to rhomboidal shaped, and covered with longitudinal epicytic folds with a density of six to eight folds/micron. The nucleus was situated in the middle of the cell, and the mucron was elongated and covered with hair-like projections; antler-like projections also extended from the anterior tip of the mucron. The distinctively large trophozoites of Trichotokara eunicae n. sp. lacked an elongated mucron and had a tadpole-like cell shape consisting of a bulbous anterior region and a tapered tail-like posterior region. The cell surface was covered with longitudinal epicytic folds with a density of three to five folds/micron. Small subunit (SSU) rDNA sequences of both species were very divergent and formed a strongly supported clade with the recently described species Trichotokara nothriae and an environmental sequence (AB275074). This phylogenetic context combined with the morphological features of T. eunicae n. sp. required us to amend the description for Trichotokara. The sister clade to the Trichotokara clade consisted of environmental sequences and Lecudina polymorpha, which also possesses densely packed epicyctic folds (3-5 folds/micron) and a prominently elongated mucron. This improved morphological and molecular phylogenetic context justified the establishment of Paralecudina (ex. Lecudina) polymorpha n. gen. et comb., (© 2012 The Author(s) Journal of Eukaryotic Microbiology © 2012 International Society of Protistologists.)

Although archigregarines are poorly understood intestinal parasites of marine invertebrates, they are critical for understanding the earliest stages in the evolution of the Apicomplexa. Previous studies suggest that archigregarines are a paraphyletic stem group from which other lineages of gregarines, and possibly all other groups of apicomplexans, evolved. However, substantiating this inference is difficult because molecular phylogenetic data from archigregarines, in particular, and other gregarines, in general, are severely limited. In an attempt to help fill gaps in our knowledge of archigregarine diversity and phylogeny, we set out to discover and characterize novel lineages of archigregarines with high-resolution light and scanning electron microscopy and analyses of small subunit (SSU) rDNA sequences derived from single-cell (SC) PCR techniques. Here, we describe two novel species of Selenidium, namely Selenidium idanthyrsae n. sp. and S. boccardiellae n. sp., and demonstrate the surface morphology and molecular phylogenetic position of the previously reported species S. cf. mesnili. We also describe a novel genus of archigregarine, Veloxidium leptosynaptae n. gen., n. sp., which branches with an environmental sequence and, together, forms the nearest sister lineage to a diverse clade of marine eugregarines (i.e. lecudinids and urosporids). This molecular phylogenetic result is consistent with the hypothesis that archigregarines are deeply paraphyletic within apicomplexans, and suggests that convergent evolution played an important role in shaping the diversity of eugregarine trophozoites., (© 2012 The Author(s) Journal of Eukaryotic Microbiology © 2012 International Society of Protistologists.)

Apicomplexans and related lineages comprise many obligate symbionts of animals; some of which cause notorious diseases such as malaria. They evolved from photosynthetic ancestors and transitioned into a symbiotic lifestyle several times, giving rise to species with diverse non-photosynthetic plastids. Here, we sought to reconstruct the evolution of the cryptic plastids in the apicomplexans, chrompodellids, and squirmids (ACS clade) by generating five new single-cell transcriptomes from understudied gregarine lineages, constructing a robust phylogenomic tree incorporating all ACS clade sequencing datasets available, and using these to examine in detail, the evolutionary distribution of all 162 proteins recently shown to be in the apicoplast by spatial proteomics in Toxoplasma. This expanded homology-based reconstruction of plastid proteins found in the ACS clade confirms earlier work showing convergence in the overall metabolic pathways retained once photosynthesis is lost, but also reveals differences in the degrees of plastid reduction in specific lineages. We show that the loss of the plastid genome is common and unexpectedly find many lineage- and species-specific plastid proteins, suggesting the presence of evolutionary innovations and neofunctionalizations that may confer new functional and metabolic capabilities that are yet to be discovered in these enigmatic organelles. [ABSTRACT FROM AUTHOR]

In this study, we describe a novel marine gregarine parasite, Selenidium oshoroense n. sp., isolated from Hydroides ezoensis Okuda 1934 (Serpulidae, Polychaeta). Trophozoites (feeding stages) of S. oshoroense n. sp. were isolated from the gut of H. ezoensis collected from the intertidal shore near Oshoro, Hokkaido, Japan, and prepared for analysis with scanning and transmission electron microscopy (SEM and TEM), and molecular phylogenetic analysis using 18S rDNA. Trophozoites of S. oshoroense n. sp. were, on average, 120 μm long and 13 μm wide. Observation of the cells under SEM and TEM revealed 23 longitudinally running epicytic folds on the surface of the cells. Peduncles, multimembrane-bound whorls, and inclusions were also observed and were indicative of surface-mediated nutrition. Myzocytotic feeding at the apical end of the cell was also indicated in sections of host gut tissue that were viewed under TEM, suggesting that myzocytosis could be a shared feature among this clade of Selenidium from tube-forming polychaetes. Molecular phylogenetic analysis of the 18S rDNA grouped S. oshoroense n. sp. within a clade of Selenidium from tube-forming polychaetes, sister to S. serpulae. The two 18S rDNA sequences generated from separate isolates of S. oshoroense n. sp. had a similarity of 0.997, but were 0.965 and 0.966 similar to S. serpulae. S. oshoroense n. sp. was differentiated from, S. serpulae, based on the absence of transverse striations on the surface of the epicytic folds and difference in ecological niche (host). Morphological differences were supported in phylogenetic analysis which grouped S. oshoroense n. sp. isolates, to the exclusion of S. serpulae. [ABSTRACT FROM AUTHOR]