Cytomorphological characteristics of Polypodium hydriforme and problems of myxozoan and cnidarian phylogeny

The present review analyses cytomorphological characters of the parasitic cnidarian Polypodium hydriforme, discriminating between those of bilateral (triploblastic) animals, common characters shared with the Myxozoa, and the unique characters of this species. Phylogenetic position of the group of parasitic cnidarians and of the class Polypodiozoa is discussed. A conclusion is made that the cytomorphological characters as well as 18S rDNA analysis of P. hydriforme and Myxozoa justify establishment of a new taxonomic group (a clade) of parasitic cnidarians (Endocnidozoa) uniting Polypodiozoa and Myxozoa (Zrzavy, Hypsa, 2003). The unique characters of P. hydriforme suggest that the phylum Cnidaria is more diverse than commonly supposed, and that P. hydriforme is not an aberrant cnidarian species but a relic organism, which might originally belong to the cnidarian class Polypodiozoa, which underwent reduction in the course of adaptation to parasitism.     

Polar filaments of Myxobolus pseudodispar spores

Spores of Myxobolus pseudodispar from plasmodia occurring in the roach muscles (Rutilus rutilus) were studied by light, transmission and scanning electron microscopy, before and after discharge of their polar filaments. Scanning microscopy reveals that discharged polar filaments bear no spines and their walls are slightly folded. Polar filaments of M. pseudodispar have been compared with stinging threads of the parasitic cnidarium Polypodium hydriforme.     

Cytological paradoxes in the developmental cycle of the coelenterate Polypodium hydriforme--an intracellular parasite from the oocytes of acipenserid fishes

Successive stages of the embryonic development of Polypodium hydriforme, occurring at the parasitic phase of its life cycle, are considered. The development of a new parasitic generation starts without fertilization, i. e. parthenogenetically. The embryo develops from aberrant binucleate gametes formed in the result of meiosis within entodermal gonads of free-living animals. This type of gametogenesis, earlier considered as spermatogenesis (Raikova, 1961), is now interpreted as oogenesis. A conclusion is drawn about a change of the sexual orientation of the male gonad which becomes a female one in the course of evolution of Polypodium. As to the gonads of free-living animals, which were formerly interpreted as female ones, they seem to be abortive rudimentary organs since they produce no mature sex cells. A long-lasting block of cytokinesis of the 2nd meiotic division, as well as utilization of the polar body of this division as a phorocyte and, later, as a trophamnion, are important adaptations of Polypodium to parasitism. It is the larger nucleus with a voluminous cytoplasm, rather than the smaller nucleus, that becomes here the 2nd polar body. Polypodium differs from other coelenterates by the presence of highly polyploid feeding cells at both the parasitic (the trophamnion, 500 c) and free-living phases of the life cycle (trophocytes in the rudimentary female gonad, 8c-32c).     

Structural characteristics of nematocyst stinging threads from the parasitic cnidarian Polypodium hydriforme

The structure of discharged nematocyst stinging threads present in free-living individuals of Polypodium hydriforme was studied by scanning and transmission electron microscopy. Not all cnidae of P. hydriforme proved to be atrichous isorhizas (as previously was accepted), but only one of the five nematocyst categories studied. A unique feature of P. hydriforme nematocysts was revealed: their stinging threads possess two strands of spines, rather than 5 or 3, as in Narcomedusae and other Cnidarians, respectively. This fact supplements the evidence in favour of P. hydriforme being a rather isolated branche in the phylogenetic tree of Cnidaria.     

Polypodium hydriforme in the eggs of the sterlet from the northern Dvina river

The paper provides data on the invasion of Acipenser ruthenus (sterlet) in the North Dvina River by Polypodium hydriforme (Cnidaria). Prevalence and intensity of invasion proved to be similar for two fishing sites. Prevalence of invasion exceeded 88%, thus being exceptionally high for P. hydriforme. Intensity of invasion was from 1 to 436 eggs per female. A verage percentage of infected eggs was about 1%.     

Amoebocytes in mesoglea of Polypodium hydriforme

Mesogleal amoebocytes of free-living Polypodium hydriforme have been studied with transmission electron microscope. The amoebocytes have numerous processes and contain cytoplasmic vacuoles with fibrous material of different density. The phenomenon of cell death (apoptosis) of mesogleal amoebocytes is described. Chromatin of dying cells becomes condensed forming picnotic "caps" in the nucleus. No mitotic cells were encountered among mesogleal amoebocytes. The origin and functions of mesogleal amoebocytes of P. hydriforme are discussed.     

Cytological aspects of similarity and difference of Myxozoa and Cnidaria

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.     

Muscular system of a peculiar parasitic cnidarian Polypodium hydriforme: a phalloidin fluorescence study

Musculature of the free-living stages of Polypodium hydriforme has been studied using phalloidin fluorescence method and confocal microscopy. P. hydriforme is a unique cnidarian possessing only smooth muscle cells situated within the mesoglea, not epithelial muscle cells, like the rest of cnidarians. Phalloidin fluorescence on whole mount preparations demonstrates an extensively developed subepidermal muscle system mostly consisting of long parallel fibers running along the tentacles. For the first time along with contracted muscle fibers we could clearly demonstrate relaxed fibers looking as long spirals. System of thin parallel circular F-actin positive fibers has been discovered outside of longitudinal muscles. The body of the animal and the mouth cone contain weakly developed parallel muscles. No special attachment of the muscle fibers to the tips of the tentacles or to the rim of the mouth has been observed. The results are discussed in connection with the "triploblastic" organization of P. hydriforme and its phylogenetic position.     

Fine structure of the nematocytes of Polypodium hydriforme Ussov (Cnidaria)

The fine structure of the stinging cells (nematocytes) and stinging capsules (nematocysts) is described for Polypodium hydriforme. a freshwater coclenterate with a prominent endoparasitie stage in its life cycle. All the nematocysts belong to the type of lesser glutinants (atrichous isorhiza) and fall into three size classes. The internal structure of the capsules is similar in the three classes. A novel type of organization of the cnidocil apparatus of the nematocysts is described. The cnidocil lacks a root fibre and its kinctosome sits directly on the operculum of the nematocyst, so that the entire cnidocil apparatus has a radial rather than bilateral symmetry. It is compared with that of other types of nematocytes and its similarity with the mechanoreccptors of the coelentcratcs is noted. The possible place of the Polypodium nematocytes in the evolution of the collar receptors of the Metazoa is discussed.     

Parasites of lake sturgeon, Acipenser fulvescens (Chondrostei: Acipenseridae), from central Canada

Nineteen species of parasites were recovered from lake sturgeon, Acipenser fulvescens, from four major waterways of Central Canada; the Saskatchewan, Nelson, Winnipeg and Rainy River systems, Twelve of these are new host records. Host specific parasites, Crepidostomum auriculatum , Diclybothrium armatum , Spinitectus acipenseri and Truttaedacnitis clitellarius , forming the core parasite species, were recovered with the highest prevalence (≥70%) and were most widely distributed. Polypodium hydriforme was recovered from only stage IV sturgeon oocytes. With the exception of Pomphorhynchus bulbocolli , prevalence and intensity of endohelminth infections were not correlated with sex or age of host but the distribution of non host-specific parasites among sampling sites was determined by the type and relative abundance of food items consumed. The parasites of lake sturgeon are closely correlated to its diet and the species of parasites recovered are more similar to those of freshwater sturgeon in Eurasia than to other species of Acipenser in North America. The present parasite community of lake sturgeon appears to have been shaped by three major factors; the presence of core parasite species which predates geographic isolation, a benthic freshwater diet which has reshaped the parasite community to one comprising freshwater species and a long association with freshwater habitats which is reflected in the reproductive isolation of the lake sturgeon and lastly, the establishment of a host-specific parasite, Spinitectus acipenseri .     

Peculiarities of the embryonic development of Polypodium hydriforme Ussov (Coelenterata), a parasite of acipenserid oocytes

"Unicellular" stages (107 specimens) and multicellular stages (64 specimens) of embryogenesis of Polypodium, found in 14 sterlet (Acipenser ruthenus L.) females, have been studied with light microscopy, cytophotometry, and autoradiography following incubation with 3H-uridine. All stages of the embryonic development occur inside host oocytes. The "unicellular" stage includes a binucleate cell with unequally sized nuclei; separation inside it of a small cell around the smaller nucleus, i.e. transformation of the single cell into a complex of 2 cells, the larger one enveloping the smaller; formation of a cavity inside the nucleus of the large (outer) cell, and migration of the small cell into it, and "cell-in-a-cell" stage, the small (generative) cell being inside the cavity formed by the nucleus of the large (trophic) cell. The latter gives rise to a hypertrophied but still unicellular envelope around the embryo, the trophamnion. The multicellular stages start with segmentation of the generative cell into blastomeres. These form a morula lying inside the cavity of the trophamnion. Gastrulation occurs by morular delamination. The inversion of the germ layers, typical of parasitic Polypodium stages, apparently arises during gastrulation. Both the generative cell ("egg") and the blastomeres are haploid, at least until the morula stage. The eggs of Polypodium are the smallest ones among coelenterates; they lack yolk and develop without fertilization. Diploidy seems to be restored during segmentation. The trophamnion cell grows, its nucleus becomes highly polypoid, and its cytoplasm accumulates mucoprotein inclusions. Both the blastomere nuclei and the trophamnion nucleus have large nucleoli and actively synthesize RNA. The stages of embryogenesis of Polypodium closely correspond to stages of the host oogenesis. The embryonic development of Polypodium lasts several years and is the slowest among coelenterates. However, it has some features typical of the class Hydrozoa.     

The nervous system of parasitic cnidarian Polypodium hydriforme

The nervous system of intracellular parasitic cnidarian Polypodium hydriforme at various stages of its life cycle has been studied by the immunocytochemical method using antibodies to FMRF-amide and by electron microscopy. Neurosecretory, sensory, and ganglion cells have been identified both at the parasitic stage (planula and stolon stages, when body layers are inverted) and in free-living animals. These cells are characterized by the presence of round neurosecretory granules about 80–120 nm in diameter. Gap junctions have been detected between nerve cells. Most of the neurosecretory and sensory cells have been observed in the epidermis of sensory tentacles of free-living animals. Sensory cells possess immobile flagella. The chains of ganglion cells are located under the epidermis and penetrate mesoglea. A centriole encircled by a fragment of nuclear envelope, which is a marker of ectodermal lineage cells in Polypodium, has been described in the cytoplasm of the sensory cells, thus proving the ectodermal nature of the nervous system. Like in most cnidarians, the nervous system of Polypodium hydriforme is a network containing FMRF-amide-like neuropeptides. Neither sense organs, nor ring-shaped nerve concentrations have been observed.     

Cladistic analysis of myxozoan species with known alternating life-cycles

The phylogenetic relationships of 15 myxozoan taxa with known alternating life-cycles were investigated in order to provide insight into the puzzling matches between myxosporeans and actinosporeans of the myxozoan life-cycle data. Phylogenetic analyses were performed using two partitioned data-sets of life-cycle stages, myxosporean stage from fish hosts versus actinosporean stage from annelid hosts, and a combined data-set of myxosporean and actinosporean stages. A cnidarian parasite of fish, Polypodium hydriforme Ussov, 1885, was used as the outgroup. The supraspecific level grouping in the conventional classification of actinosporeans was not supported in the analysis of the partitioned data from the actinosporean phase, which yielded two equally parsimonious trees. Analysis of the partitioned data from the myxosporean phase provided 24 equally parsimonious trees and did not support the current classification of myxosporeans. The analyses of the partitioned data of myxozoans by life-cycle stage revealed a lack of taxonomic congruence between the two life-stage partitions. Two equally parsimonious trees were obtained from analysis of the combined data. The suborder Variisporina of the Myxozoa was not supported by the total evidence trees, while the monophyly of the species of Myxobolus Butschli, 1882 and of the Myxidiidae were supported. The cladograms from the combined data revealed that these myxozoan species formed four major monophyletic groups. Among them, two were supported by the partitioned data of the actinosporean phase. The phylogenetic signals and the better resolution reflected by the trees of combined data suggest that the phylogenetic total evidence approach should be employed in future studies of the systematics of myxozoans.     

Ant protection of the nectaried fern Polypodium plebeium in central Mexico

Nectaries on fronds of Polypodium spp. have been studied previously only in cultivated specimens. We conducted field observations in middle-elevation forests in Mexico and found five ant species associated with nectaries of Polypodium plebeium and P. lepidotrichum. To investigate whether nectaries promote protection against herbivores, we performed ant-exclusion experiments with nectary-bearing ferns (P. plebeium) and other ferns without nectaries (Polypodium plesiosorum, P. furfuraceum, and Phlebodium pseudoaureum). When ants were excluded from the developing fronds of Polypodium plebeium, damage from foliage-feeding sawfly and lepidopteran caterpillars was significantly greater than in control fronds. Ferns without nectaries did not show a difference in damage between ant-excluded and control fronds. Our results demonstrate that fern nectaries can support ant defense of the plant body as do the extrafloral nectaries of many angiosperms.     

Correction: Phylogenetic placement of the enigmatic parasite, Polypodium hydriforme, within the Phylum Cnidaria

Correction to Evans, N.M., Lindner, A., Raikova, E.V., Collins, A.G. and Cartwright, P. Phylogenetic placement of the enigmatic parasite, Polypodium hydriforme, within the phylum Cnidaria. BMC Evol Biol, 2008, 8:139.     

Morphology,ultrastructure, and development of the parasitic larva and its surrounding trophamnion of Polypodium hydriforme Ussov (Coelenterata)

Summary The larval stage of Polypodium hydriforme is planuliform and parasitic inside the growing oocytes of acipenserid fishes. The larva has inverted germ layers and a special envelope, the trophamnion, surrounding it within the host oocyte. The trophamnion is a giant unicellular provisory structure derived from the second polar body and performing both protective and digestive functions, clearly a result of adaptation to parasitism. The trophamnion displays microvilli on its inner surface, and irregular protrusions anchoring it to the yolk on its outer surface. Its cytoplasm contains long nuclear fragments, ribosomes, mitochondria, microtubules, microfilaments, prominent Golgi bodies, primary lysosomes, and secondary lysosomes with partially digested inclusions.The cells of the larva proper are poorly differentiated. No muscular, glandular, neural, interstitial, or nematocyst-forming cells have been found. The entodermal (outer layer) cells bear flagella and contain rough endoplasmic reticulum; the ectodermal (inner layer) cells lack cilia and contain an apical layer of acid mucopolysaccharid granules. The cells of both layers contain mitochondria, microtubules, and Golgi bodies; their nuclei display large nucleoli with nucleolonema-like structure, decondensed chromatin, and some perichromatin granules. At their apical rims, the ectodermal cells form septate junctions; laterally, the cells of both layers form simple contacts and occasional interdigitations. The lateral surfaces of entodermal cells are strengthened by microtubules.     

Immunomodulation of the response to excretory/secretory antigens of Fasciola hepatica by Anapsos in Balb/C mice and rat alveolar macrophages

It is known that excretory/secretory antigens of Fasciola hepatica (ESFh) trigger a Th2-like immune response. Anapsos (A) is an aqueous hydrosoluble extract obtained from the rhizomes of the fern Polypodium leucotomos that has shown immunomodulator effects in some parasitic infections and immunological disorders. In this work we assess the effect of Anapsos and ESFh and Quillaja saponaria extract (Qs) on BALB/c mice and rat alveolar macrophages. Anapsos modulates the response of mice immunized with ESFh, decreasing IgG antibodies in A+ESFh- and A+Qs+ESFh-treated mice and triggering high levels of gammaIFN in spleen cell culture in comparison with ESFh- and Qs + ESFh--treated groups. Moreover, Anapsos showed statistically significant inhibitory effects on the nitrite production by rat alveolar macrophages prestimulated with lipopolysaccharide (LPS) as well as ESFh antigen in comparison with macrophages stimulated only with LPS. The application of ESFh and Anapsos combined avoids this inhibitory effect. Thus, Anapsos modulates the immune response against ESFh in naive mice and on the nitrite production in prestimulated rat aveolar macrophages.     

Notes on South Greenland vascular plants. Pteridophytes and gymnosperms

Taxonomical and nomenclatural notes worked out during a phytogeographical study of South Greenland are published. It is shown that the Greenland representative of Polypodium belongs to the American P. virginianum and not to the Eurasian P. vulgare. The following changes are made: Diphasiastrum complanatum (L.) Holub f. montellii (Kukk.) J. Feilberg comb, et stat. nov. and Isoetes lacustris L. ssp. pauper–cula (Engelm.) J. Feilberg stat. nov. The last mentioned change has to be made here when treating ssp. lacustris , which is the taxon present in Greenland.     

Polypodoaurein,a new phytoecdysone from Polypodium aureum L.

A new phytoecdysone was isolated from Polypodium aureum L. and its structure determined as 25-O-methylecdysterone.     

Redescription of Rhamnocercus stichospinus Seamster and Monaco, 1956 (Monogenea: Diplectanidae), parasitic on Menticirrhus americanus (Osteichthyes: Sciaenidae) from the coastal zone of the State of Rio de Janeiro, Brazil.

Rhamnocercus stichospinus Seamster and Monaco, 1956 (Diplectanidae) parasitic on the sciaenid fish Menticirrhus americanus from the coastal zone of the State of Rio de Janeiro, is redescribed and recorded for the first time in the South American Atlantic Ocean. The generic diagnosis of Rhamnocercus is emended to accommodate the presence of confluent intestinal ceca in R. stichospinus.