[The history of myxosporean (Myxozoa Grasse, 1970, Myxosporea Butschli, 1881) life and nuclear cycles studies].

The paper presents a historic review of various hypothesis concerning the myxozoan life and nuclear cycles. The comparison of DAPI- and Feulgen-image-cytometry results of DNA amount in myxozoan actinospora and myxospora nuclei, in connection with the new data on the animal life and nuclear cycle, has been performed. Possible reasons for the data discrepancy are considered. The further perspectives of myxozoan biology, cytology, karyology and taxonomy investigation in Russia are discussed.

[Cytological aspects of similarity and difference of Myxozoa and Cnidaria]. / Tsitologicheskie aspekty skhodstva i razlichiia miksosporidii i knidarii.

A comparative cytomorphological analysis of Myxozoa and parasitic Cnidaria Polypodium hydriforme has been carried out in view of the Weill (1938) hypothesis, which regards Myxozoa as a reduced Cnidaria. The question on the relation of Myxozoa and Cnidaria was arising several times with the application of some new methods during the Myxozoa studies. At present the idea on their phylogenetic relationships has appeared again in connection with an absolutely new understanding of the myxozoan life cycle (Wolf, Markiw, 1984), as well as with the application of molecular-biological methods for their phylogenetic studies. The latter, however, provided some diverse results. So far no comparative cytomorphological analysis of Myxozoa and Polypodium has been carried out. The present paper is to fill the gap on the basis of accumulated facts. According to Weill (1938), the features of similarity of parasitic Cnidaria and Myxozoa are the following: 1) the presence in both of extrusomes (nematocysts and polar capsules) whose structure and development are surprizingly similar; 2) the nuclear dimorphism and somato-generative segregation; 3) the presence of a somatic nutritional cell, surrounding the multiplying generative cells; at present it is known that polyploidy of somatic nuclei and the absence of parasitophorous vacuole are characteristic of trophamnion of Polypodium and trophozoite of Myxozoa; 4) the presence of radial symmetry in both groups; 5) the construction of a diblastic organism made of a cluster of endodermal cells and a few ectodermal cells; 6) the similarity of their cell contacts (Grassé, 1970). At present it is possible to add to Weill's (1938) list of features common for parasitic Cnidaria and Myxozoa the number of important similarities between Polypodium and Myxozoa, some of which being not characteristic of Cnidaria: 1) the "cell in cell" organization of all Polypodium parasitic stages and all Myxozoa life cycle stages; 2) the presence of gametophore supplied with extrusomes; 3) both organisms have haplophase in their life cycles preceded by two-step meiosis; 4) there are mitochondria with tubular cristae in both organisms; 5) the absence of spermatozoa and eggs in both organisms; 6) the similarity of Polypodium cnidocile structure and the cone-like formation situated at the anterior end of polar capsule of actinospore (Lom. Dykova, 1997); 7) the participation of MTOC in the formation of extrusomes in both animals. In spite of the obvious similarity between Myxozoa and parasitic Cnidaria (including Polypodium) it is, however, necessary to take into account differences between them, the main being as follows: the absence in Myxozoa of flagellated stages, centrioles, tissues and organs, true blastophylla, planula-like larvae, gastrulation; the presence of low cell integrations in Myxozoa; Cnidaria and Myxozoa have different types of mitosis, their life cycles and the discharge mechanism of their stinging apparatus being also different. We consider as quite valid a suggestion by Siddall et al. (1995) that parasitic Cnidaria could present an early separated branch of the cnidarian evolution. Further studies of Myxozoa life cycle may show their more definite relation to parasitic Cnidaria. The problem has not yet been solved completely since the available molecular-biological data are rather contradictory and moreover there is no distinct idea as to the Eumetazoa ancestor so far. A further thorough investigation is badly needed in the feelds of developmental cycle, cytomorphology and molecular biology of the variety of narcomedusae and representatives of Myxozoa. This may help to find some transitional forms and stages of the animals and to understand whether we deal with a regressive evolution of parasitic Cnidaria or with a parallel evolution of taxa originated from the common ancestor.

[Ploidy of somatic nuclei during life cycle of Myxosporean (Myxozoa, Grasse, 1970)]. / Ploidnost' somaticheskikh iader na ptotiazhenii zhiznennogo tsikla mik sosporidii (Myxozoa, Grasse, 1970)

Results of the author's investigation on the ploidy of somatic nuclei in various myxosporean species, throughout different stages of their complicated life cycles, have been summarized. A comparative analysis of data on the ploidy in somatic and generative nuclei of Kudoa quadratum (Multivalvulida) has been given for the first time. Representatives of the Multivalvulida order differ from those of the earlier studied Bivalvulida order in the structure of their myxospore. It has been found that during the myxosporean life cycle alteration of haploid, diploid and polyploid somatic nuclei occurs, and that differentiation of somatic cells and nuclei takes place in both haploid and diploid phases of the life cycle.

[A comparison of the amount of DNA in the sporoplasm nuclei of the myxosporidian and actinosporidian phases of the life cycle of the parasitic protozoan Zschokkella nova--a representative of the Myxozoa type]. / Sravnenie kolichestva DNK v iadrakh sporoplazm miksosporeinoi i aktinosporeinoi faz zhiznennogo tsikla paraziticheskogo prosteishego Zschokkella nova--predstavitelia tipa Myxozoa.

Average DNA amounts in sporoplasm nuclei of the actinosporean and myxosporean developmental phases of Z. nova were compared. The average DNA amount per one, presumably diploid, sporoplasm nucleus of the actinosporean phase spores was twice as large as the average summarized DNA amount in two, presumably haploid, nuclei of the myxospsorean phase spores of Z. nova. It is suggested that sporoplasm nuclei in the actinosporean phase spores of Z. nova are diploid postsynthetic, whereas sporoplasm nuclei of the myxosporean phase spores are haploid. The data do not contradict the earlier supposition (Uspenskaya, 1955a, 1955b), that the investigated spores may be developmental stages of the same organism. The data support the idea of haploidy of the myxosporean phase spores (Uspenskaya, 1984) and diploidy of the actinosporean phase spores (Marques, 1984) in Myxozoa.

[Biological characteristics of the invasive stage of Myxosoma cerebralis (Myxosporidia: Myxosomatidae)]. / Biologicheskie osobennosti invazionnoi stadii Myxosoma cerebralis (Myxosporidia: Myxosomatidae).

The data concerning biological peculiarities of spores of Myxosoma cerebralis obtained by the author and other researchers are summarized. The life cycle of M. cerebralis is well adapted to the seasonal cycle of the host owing to the fact that the infectivity of the spores is attained only after 4 months of aging in water and that the spores are highly resistive to freezing and drying. No sexual process during 4 month aging was observed. It is supposed that the maturity of spores depends to a great extent on the ability of polar capsules for extrusion.

[Cytophotometric studies of the nuclear cycle of Sphaeromyxa elegini]. / Tsitofotometricheskie issledovaniia iadernogo tsikla mikrosporidii Sphaeromyxa elegini

The cytophotometric investigation of DNA content in the nuclei of Myxosporidia Sphaeromyxa elegini Dogiel 1948 was made. It was found that not only nuclei of sporoplasm but also capsulogenic nuclei are haploid. The fact makes us leave apart, as far as these species are concerned, the scheme of nucl eic cycle according to which all somatic nuclei are diploid. It seems possible that two nuclei of sporoplasm as well as two capsulogenic nuclei are the four products of two-step meiosis, but lacking the data on DNA content in valvogenic nuclei we cannot be sure of this. It spite of some peculiarities in the distribution according to DNA content it seems that sporoblasts nuclei cna be considered as diploid at all the stages investigated. The vegetative nuclei are polyploid (tetraploid as usual).