The subkingdom Protozoa now inclues over 65,000 named species, of which over half are fossil and approximately 10,000 are parasitic. Among living species, this includes approximately 250 parasitic and 11,300 free-living sarcodines (of which approximately 4,600 are foraminiferids); approximately 1,8000 parasitic and 5,100 free-living flagellates; approximately 5,600 parasitic "Sporozoa" (including Apicomplexa, Microspora, Myxospora, and Ascetospora); and approximately 2,5000 parasitic and 4,700 free-living ciliates. There are undoubtedly thousands more still unnamed. Seven phyla of PROTOZOA are accepted in this classification--SARCOMASTIGOPHORA, LABYRINTHOMORPHA, APICOMPLEXA, MICROSPORA, ASCETOSPORA, MYXOSPORA, and CILIOPHORA. Diagnoses are given for these and for all higher taxa through suborders, and reporesentative genera of each are named. The present scheme is a considerable revision of the Society's 1964 classification, which was prepared at a time when perhaps 48,000 species had been named. It has been necessitated by the acquisition of a great deal of nex taxonomic information, much of it through electron microscopy. It is hoped that the present classification incorporatesmost of the major changes that will be made for some time, and that it will be used for many years by both protozoologist and non-protozoologists.

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The phylum Myxozoa has been considered to comprise two classes, Myxosporea Bütschli, 1881 (primarily of fishes) and Actinosporea Noble in Levine et al., 1980 (primarily of aquatic oligochaetes). About 10 years ago it was demonstrated that the life cycle of Myxobolus cerebralis Hofer, 1903 (Myxobolidae: Platysporina) of salmonid fishes requires transformation of the myxosporean into an actinosporean stage in the oligochaete worm Tubifex tubifex (Tubificidae), and that the stage infective to fish is the actinosporean spore. This type of two-host life cycle has now been demonstrated or strongly implicated for 14 myxosporean species, belonging to 6 genera in 4 families. In light of these findings, the taxonomy of the Myxozoa is revised. We propose the following: suppression of the newer class Actinosporea and the order Actinomyxidia Štolc, 1899; and suppression of all families in the Actinosporea except Tetractinomyxidae. This family and its one genus, Tetractinomyxon Ikeda, 1912, are transferred to the order Multivalvulida Shulman, 1959 (Myxosporea). We also propose that actinosporean generic names be treated as collective-group names, thus they do not compete in priority with myxosporean generic names. Triactinomyxon dubium Granata, 1924 and Triactinomyxon gyrosalmo Wolf and Markiw, 1984 are suppressed as junior synonyms of Myxobolus cerebralis. The myxosporean stage of no other previously named actinosporean has been identified. Other actinosporean species are therefore retained as species inquirendae until their myxosporean stages are identified. A revised description of the phylum Myxozoa is provided that includes our proposed taxonomic and nomenclatural changes.

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SYSOPSIS.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 X 2 p , 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 smoothmembraned vesicles appear in the plasm. These vesicles fuse to make the outer membrane of the filament. Later, its inner structures originate-the axial eleotron-dense substance, filling the hollow lumen ENEWED interest in the cytology of protozoan species R assignable to the class Microsporidea is reflected in the recent series of papers dealing with the fine structure of their spores ( 1,7,9,12,13,(15)(16)(17). Thanks to these studies on several types of microsporidian spores, their essential components are known: a shell composed of several layers; a. coiled polar filament whose basal part is joined with the apolar cap at the anterior pole of the spore; an anteriorly located swelling organelle, the polaroplast ; a fluid-filled vacuole at the posterior end of the spore; and, finally, the sporoplasm itself. An explanation of the role these organelles )lay during filament extrusion, discharging the sporoplasm, has also been offered(13), based on experiments with 2xtrusion: after the spore has been activated, the polaro->last quickly imbibes water from the environment. This :awes a considerable intrasporal pressure, forcing the holow filament to evaginate-the fluid of the posterior vacu-3le plays an important role-thru the anterior end of the ,hell, while the sporoplasm is being pushed thru the whole length of the filament out of the spore. Some of the stages If this process need further clarification, and additional -esearch on the structure of the ripe spore, especially on :he filament's fine structure, seems necessary.With respect to electron-microscopic studies of the de-:elopmen t cycles of microsporidians which might reveal .he origin of the highly specialized structures of the spore, LS well as make possible a comparison with development n groups such as those comprising the myxosporidians or iaplosporidians, only few studies have appeared to date. The observations of de Puytorac( 16) on Mrazekia lumbri-7uli and of VBvra(22) on the genera Thelohank and 141 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 polmoplast 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 r...

In the last 30 years, at various laboratories in the United States, France and England, many strains of small holotrichous ciliates have been established in axenic culture for use in a widening variety of investigations of a physiological or biochemical nature. Since few of these organisms have been adequately described or properly identified by the workers employing them, thus making difficult meaningful comparison of the various experimental results reported, the need for morphological and taxonomical study has become increasingly apparent. At least twenty-nine such axenic strains of ciliates, considered members of a ‘Colpidium-Glaucoma-Leucophrys-Tetrahymena group’ because it has been principally to these four genera that the protozoa have been assigned in the past, are still in existence and twenty-six of them were collected for use in the present investigation. For accurate identification of such relatively undifferentiated ciliates the use of silver nitrate impregnation techniques, the value of which was recognized some years ago by Klein (1926) and stressed by Furgason (1940), is re-emphasized as being nearly indispensable. Details of buccal organelles and differentiated pellicular structures in other parts of the body are revealed precisely and with constancy.