This review summarizes data on the biogeography and dispersal of bacteria, microfungi and selected protists, such as dinoflagellates, chrysophytes, testate amoebae, and ciliates. Furthermore, it introduces the restricted distribution and dispersal of mosses, ferns and macrofungi as arguments into the discussion on the postulated cosmopolitism and ubiquity of protists. Estimation of diversity and distribution of micro-organisms is greatly disturbed by undersampling, the scarcity of taxonomists, and the frequency of misidentifications. Thus, probably more than 50% of the actual diversity has not yet been described in many protist groups. Notwithstanding, it has been shown that a restricted geographic distribution of micro-organisms occurs in limnetic, marine, terrestrial, and fossil ecosystems. Similar as, in cryptogams and macrofungi about, 30% of the extant suprageneric taxa, described and undescribed, might be morphological and/or genetic and/or molecular endemics. At the present state of knowledge, micro-organism endemicity can be proved/disproved mainly by flagship species, excluding sites (e.g., university ponds) prone to be contaminated by invaders. In future, genetic and molecular data will be increasingly helpful. The wide distribution of many micro-organisms has been attributed to their small size and their astronomical numbers. However, this interpretation is flawed by data from macrofungi, mosses and ferns, many of which occupy distinct areas, in spite of their minute and abundant means of dispersal (spores). Thus, I suggest historic events (split of Pangaea etc.), limited cyst viability and, especially, time as major factors for dispersal and provinciality of micro-organisms. Furthermore, the true number of species and their distribution can hardly be estimated by theories and statistics but require reliable investigations on the number of morphospecies in representative ecosystems. Generally, the doubts on Beijerinck's famous metaphor "in micro-organisms everything is everywhere" can be focussed on a simple question: If the world is teeming with cosmopolitan unicells, where is everybody?

Biogeography and Dispersal of Micro-organisms: A Review Emphasizing Protists

A synopsis of 744 nominal species of Myxobolus Butschli, 1882 (Myxozoa, Myxosporea, Myxobolidae) is presented. For each species, the relevant morphometric and morphological data are indicated, as well as the host(s), site(s) of infection within the host and type-locality.

Synopsis of the species of Myxobolus Butschli, 1882 (Myxozoa: Myxosporea: Myxobolidae).

Considerable knowledge of microsporidian structure has been accumulated during 150 years of research. Critical evaluation of this knowledge reveals, however, that most progress has been achieved during the past fifteen years after electron microscopic application. Although some light microscope observations have contributed amazingly accurate data on microsporidian structure, the extreme smallness of microsporidia (the spores of which are probably the smallest eukaryotic cells) as well as the compactness and complexity of their structural organization requires better resolution than that obtained with the light microscope.

Structure of the Microsporidia

Parasitism, aptly defined as one of the 'living-together' strategies (Trager, 1986), presents a dynamic system in which the parasite and its host are under evolutionary pressure to evolve new and specific adaptations, thus enabling the coexistence of the two closely interacting partners Microsporidia are very frequently encountered obligatory intracellular protistan parasites that can infect both animals and some protists and are a consummate example of various aspects of the 'living-together' strategy Microsporidia, relatives of fungi in the superkingdom Opisthokonta, belong to the relatively small group of parasites for which the host cell cytoplasm is the site of both reproduction and maturation The structural and physiological reduction of their vegetative stage, together with the manipulation of host cell physiology, enables microsporidia to live in the cytosolic environment for most of their life cycle in a way resembling endocytobionts The ability to form structurally complex spores and the invention and assembly of a unique injection mechanism enable microsporidia to disperse within host tissues and between host organisms, resulting in long-lasting infections Microsporidia have adapted their genomes to the intracellular way of life, evolved strategies how to obtain nutrients directly from the host and how to manipulate not only the infected cells, but also the hosts themselves The enormous variability of host organisms and their tissues provide microsporidian parasites a virtually limitless terrain for diversification and ecological expansion This review attempts to present a general overview of microsporidia, emphasising some less known and/or more recently discovered facets of their biology

Microsporidia and ‘The Art of Living Together’

Parasites have a major impact on global finfish and shellfish aquaculture, having significant effects on farm production, sustainability and economic viability. Parasite infections and impacts can, according to pathogen and context, be considered to be either unpredictable/sporadic or predictable/regular. Although both types of infection may result in the loss of stock and incur costs associated with the control and management of infection, predictable infections can also lead to costs associated with prophylaxis and related activities. The estimation of the economic cost of a parasite event is frequently complicated by the complex interplay of numerous factors associated with a specific incident, which may range from direct production losses to downstream socio-economic impacts on livelihoods and satellite industries associated with the primary producer. In this study, we examine the world's major marine and brackish water aquaculture production industries and provide estimates of the potential economic costs attributable to a range of key parasite pathogens using 498 specific events for the purposes of illustration and estimation of costs. This study provides a baseline resource for risk assessment and the development of more robust biosecurity practices, which can in turn help mitigate against and/or minimise the potential impacts of parasite-mediated disease in aquaculture.

Economic costs of protistan and metazoan parasites to global mariculture

SYNOPSIS. A sequence of developmental stages of Plistophora hyphessobryconis Schaperclaus, a microsporidian protozoan parasite of the muscular tissue of several species of freshwater fishes, was studied with the electron microscope. The youngest stages observed, ca. 4 × 2 μ, have a single nucleus and their plasm contains only ergastoplasmic lamellae and ribosomes. They are surrounded by a halo of lysed host tissue. They increase in volume to become large sporonts with a great number of nuclei and a thick, 2-layered membrane. Thru schizogony, a corresponding number of sporoblasts is produced within this pansporoblast membrane. Sporoblasts start to develop a thick spore membrane, and a number of smooth-membraned vesicles appear in the plasm. These vesicles fuse to make the outer membrane of the filament. Later, its inner structures originate—the axial electron-dense substance, filling the hollow lumen of the filament, and a middle, electron-transparent layer. The structure of the filament is discussed in relation to its function and with regard to the findings of other authors.



The polaroplast is a laminated structure, originating possibly by transformation of endoplasmic reticulum; the polar cap forms its apical part. The cap is also lamellar; its substance reaches into the lumen of the filament for a certain distance. No micropyle was discovered in the shell; the filament is fastened to the polar cap. These observations on microsporidian development and on the structure of their spores are compared with similar data on myxosporidian species. Such a comparison speaks clearly in favor of the complete taxonomic separation of the Microsporidea from the Myxosporidea, the latter being quite different also from other sporozoa sensu lato.

Ultrastructural Observations on the Development of the Microsporidian Protozoon Plistophora hyphessobryconis Schaperclaus

North American Trichodina from Carassius auratus, Lepomis cyanellus, L. macrochirus, Micropterus salmoides, and Rhinichthys atratulus have been studied by the silver-impregnation method and compared with European species. T. reticulata Hirschmann and Partsch, 1955, and T. (Foliella) subtilis Lorn, 1959, originally described from European goldfish, are herein recorded from North America also. T. fultoni Davis, 1947, from Lepomis cyanellus, Micropterus salmoides, and Rhinichthys atratulus is redescribed, and T. domerguei f. magna Lorn, 1961, described from European tench and gudgeon, is considered a synonym. A Trichodina sp. from the gills of Lepomis macrochirus is described; it is almost identical with T. nigra Lom, 1961 from European Rutilus, T. discoidea from centrarchids, and T. tumefaciens from Cottus of North America. Other North American trichodinids are reviewed briefly. Up to the present time, more than 90 species of Trichodina have been described from the gills and skin of marine and freshwater fishes. Many of them have been considered as new only because they were found in a different host and remote geographic area. The descriptions in many cases were inadequate since the uniform body structure of these ciliates yields few characters for solid differentiation of species. However, the recently employed Klein's silver-impregnation technique (Lorn, 1958; Raabe, 1959) clearly reveals details of the adhesive disc which are important features of urceolariid taxonomy. This, together with careful biometrical and other morphological information, represents a good base for taxonomic studies of this group. It is beyond the scope of this communication to present all the problems of trichodinid taxonomy; they can be found in Uzmann and Stickney (1954), Raabe (1959), and Lorn (1958, 1961, 1962). Though insufficient description of some species does not permit us to identify them again, reexamination of a number of species which have been accurately characterized by older methods is possible. This is a study on the geographic distribution of some fish trichodinids, based on a comparison of four species Received for publication 9 April 1963. 30 from some North American fishes from Pennsylvania and West Virginia with material from Cz choslovakia. Trichodina reticulata Hirschmann and

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Geographic distribution of some species of trichodinids (Ciliata: Peritricha) parasitic on fishes

SYNOPSIS. Brooklynella hostilis is a new genus and new species of highly lethal Chilodonella-like parasite in the gills of marine fishes. It differs from other dysteriid ciliates by a combination of these features: 1) posterior-ventral adhesive apparatus consisting of a single glandular organelle that lacks a distinct discharging canal or podite; 2) the kinetosomes cover the entire ventral surface, except the left posterior portion of the body; the outer right kinety is divided into 2 segments; the middle postoral kinetyues as a row of kinetosomes without cilia around the glandular organelle; 3) there are never more than 9 nematodesmata; and 4), there are numerous small micronuclei. The lesions caused by the infection vary from a mild inflammatory reaction to extreme tissue damage resulting in severe hemorrhages, desquamation, and fusion of the gill lamellae.

Brooklynella hostilis n. g., n. sp., a Pathogenic Cyrtophorine Ciliate in Marine Fishes*

The spore of Myxosoma cerebralis is redescribed and compared with that of a close relative, M. cartilaginis. M. cerebralis is smaller, with greater variability in size and shape. It possesses a mucous envelope whereas M. cartilaginis does not. The surface architecture of M. cerebralis, as seen with the scanning electron microscope, differs in possessing a conspicuous circumsutural groove, prominent polar filament pores, and a mucous envelope.

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Jiri Lom

Papers

Ultrastructural Observations on the Development of the Microsporidian Protozoon Plistophora hyphessobryconis Schaperclaus

Geographic distribution of some species of trichodinids (Ciliata: Peritricha) parasitic on fishes

Brooklynella hostilis n. g., n. sp., a Pathogenic Cyrtophorine Ciliate in Marine Fishes*

Morphology of the spores of myxosoma cerebralis (hofer, 1903) and m. cartilaginis (hoffman, putz, and dunbar, 1965)*