The notion that members of the phylum Myxozoa Grassé, 1970 do not properly belong in classifications of protists has frequently been suggested because the infective spores of these parasites are not unicellular. Systematists have failed to be decisive about myxozoan phylogenetic affinities, either finding the suggestion of a cnidarian connection to be preposterous or considering the recent suggestion of a relationship with nematodes to be an obvious failure of molecular phylogenetics. Thus, the group has remained in classifications as a protistan phylum in its own right. The ultrastructure of the development of myxozoans was critically re-examined in order to more fully explore the possibility of morphological synapomorphies with metazoan taxa. These morphological characters, in combination with small ribosomal subunit gene sequences, were used in a phylogenetic analysis in order to assess myxozoan origins. The results unequivocally support the inclusion of myxozoans as a clade of highly derived parasitic cnidarians, and as sister taxon to the narcomedusan Polypodium hydriforme. Reassessment of myxozoans as metazoans reveals terminal differentiation, typical metazoan cellular junctions, and collagen production. Their "polar capsules" are redescribed as typical nematocysts bearing atrichous isorhiza. Insofar as taxa cannot be contained within other taxa of equal rank, the phylum Myxozoa is abandoned and it is recommended that the group as a whole be removed from all protistan classifications and placed in a more comprehensive cnidarian system.
The geographic distribution of metazoan parasites of American eels (Anguilla rostrata) was determined from 28 sites in the Southern Upland and adjacent regions of Nova Scotia. Twelve parasite species were encountered. Component community diversity as measured by species richness, Shannon-Wiener index (H') and Hill's number (N1) decreased when pH < 5.4. Seven species (Azygia longa, Crepidostomum brevivitellum, Bothriocephalus claviceps, Proteocephalus macrocephalus, Paraquimperia tenerrima, Echinorhynchus salmonis, Ergasilus celestis) were found in both the Southern Upland and adjacent watersheds to the north. Three species (Pseudodactylogyrus anguillae, Diplostomum sp., Pomphorhynchus bulbocolli) were found only at sites beyond the Southern Upland, which flowed into the Bay of Fundy and had high pH values ( > 5.4). Two species (Daniconema anguillae, Echinorhynchus lateralis) were limited to sites within the Southern Upland. Digeneans were absent from rivers in the southwest with pH values < 4.7. Variation in occurrence of parasite species was observed among rivers within a single watershed and among years within individual sites. Nevertheless, the impact of acidity at the local level was observed regionally across the Southern Upland of Nova Scotia. These data support the hypothesis that parasite assemblages may be good indicators of environmental stress.
Attachment-site pathology of the ectoparasites Gyrodactylus adspersi Cone and Wiles, 1983 on Tautogolabrus adspersus, Gyrodactylus avalonia Hanek and Threlfall, 1969 on Gasterosteus aculeatus, Gyrodactylus bullatarudis Turnbull, 1956 on Poecilia reticulata, Gyrodactylus sp. on Carassius auratus, and Gyrodactylus salmonis (Yin and Sproston, 1948) on Salmo gairdneri was examined using optical microscopy and scanning electron microscopy. In the first four species, the disc-shaped haptor attached itself to the host skin surface by means of blade tips of 16 peripherally located marginal hooks, with the two ventrally located hamulus blades compressing the underlying epithelium into a small depression. Tissue damage from attachment and feeding was minimal. However, G. salmonis lodged its marginal hook sickles deep into the host epidermis and appeared to cause extensive fin damage and skin discoloration. There was little evidence of bacterial involvement in the wounds, but bacterial microcolonies were observed on the body surface and haptor of G. salmonis. The latter results are discussed in relation to our understanding of gyrodactyliasis.
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