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SUMMARYThis work reports a new type of actinospore, Unicapsulactinomyxon, which exhibits a unique morphological characteristic in that it has a single and large polar capsule (9·3×4·1μm) (which possesses a longitudinally-folded polar filament) instead of the 3 polar capsules previously described for actinosporeans. The spore has a binucleated sporoplasm and 3 valves, each of which forms a long process. The spore has a total length of 241·3μm. This parasite develops in groups of 8 inside pansporocysts in the coelomic cavity of the polychaete host. Molecular investigations on the SSU rDNA show that the new actinospore type is most closely related toEnteromyxumspecies (81–84% similarity). A survey of actinospore infections of the marine polychaeteDiopatra neapolitanain 2007 and 2009, in the Aveiro Estuary (Portugal), showed an annual prevalence of 1·0% and 0·3%, respectively.

SUMMARYA Minchinia sp. (Haplosporidia: Haplosporidiidae) parasite was identified infecting rock oysters and morphologically described by Hine and Thorne (2002) using light microscopy and transmission electron microscopy (TEM). The parasite was associated with up to 80% mortality in the host species and it is suspected that the parasite would be a major impediment to the development of a tropical rock oyster aquaculture industry in northern Western Australia. However, attempts to identify the parasite following the development of a specific probe for Haplosporidium nelsoni were unsuccessful. The SSU region of the parasite's rRNA gene was later characterized in our laboratory and an in situ hybridization assay for the parasite was developed. This study names the parasite as Minchinia occulta n sp. and morphologically describes the parasite using histology, scanning electron microscopy and transmission electron microscopy. The non-spore stages were unusual in that they consisted primarily of uninucleate stages reminiscent of Bonamia spp. The parasite's spores were ovoid to circular shaped and measured 4·5 μm–5·0 μm×3·5–4·1 μm in size. The nucleus of the sporoplasm measured 1·5–2·3 μm and was centrally located. The spores were covered in a branching network of microtubule-like structures that may degrade as the spore matures.

A new histozoic species of myxosporean was found to infect the gill filaments, gut, kidney and liver of the freshwater teleost Leporinus friderici, collected from the estuarine region of the Amazon, near the city of Belém, Brazil. The plasmodia show asynchronous development, at any one time composed of mature spores and all sporogonic stages. The ellipsoidal spore body, measuring 10·4 μm long and 5·7 μm wide, consists of 2 equal shell valves adhering together along the straight suture line. Each valve has a caudal process measuring 23·3 μm in length. There are 2 symmetric polar capsules, without intercapsular appendix, measuring 5·0 μm×2·1 μm, and each has a polar filament with 7–8 coils. In general, ultrastructural details of sporoblast and spore development are in agreement with previously described myxosporeans. Some ultrastructural aspects such as cellular alterations of the pericyte in the different organs infected and characterization of the sporoplasmosomes during the sporoplasm maturation are described. This parasite was studied under light and electron microscope and compared with others species of the genus Henneguya, considering also host specificity. From our observations we propose the creation of a new species, Henneguya friderici n. sp.

SUMMARYSphaerospora molnari sp.nov. is described from the gills, skin and nasal pits of yearling carp (Cyprinus carpio L.) from ponds in the South Bohemian pond region of Czechoslovakia and one infected specimen from the river Danube in Bulgaria. Small vegetative stages, often massively pervading the infected tissue, produce 1 spore each. Spores are sub-spherical, 10·3 × 10·5 μm in size, with almost spherical polar capsules of equal size. The polar filaments are wound in wide coils that are almost parallel with the longitudinal axis of the spore. There are 2 uninucleate sporoplasm cells. Developmental stages and spores are also found in circulating blood. In the gills, S. molnari invades stratified epithelium of gill filaments and secondary lamellae causing branchial lesions and must be regarded as a serious pathogen of yearling carp. A new name, Sphaerospora chinensis sp.nov. is proposed for S. branchialis Lee & Nie in Chen (1973), pre-occupied by S. branchialis Razmashkin and Skrip-chenko, 1967.

This study examines the ultrastructure of the posterior vacuole in frozen-etched spores of Thelohania bracteata (Nosematidae), a microsporidian infecting the fat body of larval black-flies (Simuliidae). This organelle, considered important in providing intrasporal pressure for sporoplasm extrusion through the polar filament, has a double membrane with particles on its internal faces as revealed by the freeze-etching technique. The size and pattern of these particles differ from those in membranes of the polar filament and nucleus, and this difference may have functional significance. The posterior vacuole, and also the polaroplast, may originate from expanded sacs that occur in the immature spore. There is evidence from this study that there are many basic ultrastructural similarities between spores of different microsporidian species and that at least some reported differences are the result of varying techniques.We gratefully acknowledge the freeze-etching facilities provided by the Department of Pathology, Faculty of Medicine, McMaster University. The research was supported by Grant A-130 from the National Research Council of Canada.

1. Studies on two Microsporidia, Nosema helminthorum Moniez and N. locustae Canning, have shown that the polar filament serves to conduct the sporoplasm out of the spore.2. The filament is a solid structure and the sporoplasm is either attached to or is a continuation of it. The filament is first extruded as a tightly coiled mass and, as this uncoils, it drags the sporoplasm out of the spore.3. The sporoplasm, which is either uninucleate or binucleate, takes the form of a girdle of protoplasm, which lies on the inner side of the spore membrane and surrounds the coiled polar filament. There is no polar capsule.

1. A brief outline of the life cycle of a species of Nosema parasitic in Saturniid moths is given. It is of the normal type.2. The structure of the spore is described, and from electron microscopy evidence is presented which supports the theory that the sporoplasm is injected into the host's tissue.3. The volume of the spore is affected by the ambient medium, by the pretreatments of fixation and of desiccation, by the site of development within the host and by the age of the host.4. These results have been discussed with reference to the use of spore size as a diagnostic character in the classification of the Microsporidia. It is concluded that spore size is not a reliable character for taxonomic purposes.