|Other Abstract||As an important group of the pathogenic protozoa, the parasitic ciliates can obligately or facultatively infect the gills, skins, muscles or internal organs of various aquatic animals and do harm to the hosts in varying degrees. Many reports indicate great losses in both freshwater and marine aquaculture industry caused by parasitic ciliates. However, our knowledge to this group remains in the stage of alpha taxonomy. Little attention has been given to the phylogenetic relationships of these ciliates. In this dissertation, the phylogeny of some freshwater parasitic ciliates with both morphological and molecular markers is studied. The main results and conclusions are summarized as follows:
1. The revision of the genus name, morphology and life-cycle, determination key, relationship between Apiosoma and their hosts were reviewed respectively. The morphology and structure of A. piscicola were well described and lots of bacteria and food particles were observed within the body of the organisms, especially around the peristomial disc. This phenomenon give a strong support from the aspect of food sources to the viewpoint that Apiosoma is a kind of ectocommensals but not ectoparasites. Twelve morphometric parameters were used to describe this peritrich in detail and comparisons were made with other reports. Its synonyms, Glossatella cylindriformis Chen, 1955 and Apiosoma magna Banina, 1968 were clarified based on reliable data. A. piscicola was still considered somewhat host-specific by us, especially to cyprinids, although it shows a quite wide limit of host variability. The telotroch was also observed, and its structures were described. Besides, the difficulties of the generic taxonomy were discussed and some suggestions were given.
2. Redescription of Balantidium ctenopharyngodoni Chen, 1955 collected from the hindgut of grass carp from Honghu Lake were well presented at both light and electron microscopic levels. Some revisions were done: the vestibulum is fairly symmetrical, with compactly arranged cilia rather than assembled membrane bordering on the left vestibular side; four contractile vacuoles actually exist in the latter body. Its fine structure was described in detail with an emphasis on its somatic cortex and vestibulum. A pattern of a two dimensional system that constitutes the elaborate cortex architecture was firstly put forward. Besides, the cysts of B. ctenopharyngodoni were observed, and its possible infection routes were also discussed.
3. The unique body shape of Balantidium polyvacuolum Li, 1963-highly arched dorsal side and flattened ventral surface as well as its remarkable concave platelet present in the centroventral were well described. Two types of vestibulum shape were observed, which may suggest the existence of two subspecies or genotype species of these balantidia. The 18S rDNA of B. polyvacuolum and B. ctenopharyngodoni were sequenced herein and phylogenetic analysis of the subclass Trichostomatia was conducted. The result indicated that the subclass Trichostomatia is monophyletic while the oder Vestibuliferida and Balantidium spp. showed their paraphyly. As to the phylogenetic position, the genus Balantidium should be recognized as a higher taxon.
4. Two ciliated protozoa, Balantidium sinensis Nie, 1935 and Balantidium andianusis n. sp., were isolated from the feces of a wild Chinese giant salamander (Andrias davidianus) captured from the mountainous area of Shiyan, Hubei Province, Central China in October 2006. The occurrence of B. sinensis in A. davidianus should be a new record because the type specimens were first discovered and named by Nie in 1935 from Rana nigromaculata and R. plancyi. B. andianusis n. sp. was considered to be a new species based on its unique morphological characteristics, especially the high length/width ratio of the vestibulum (8:1). Comparisons were also made among Balantidium species that were found from urodele amphibians. To our knowledge, it is the first report of Balantidium species inhabiting Cryptobranchoidea amphibians.
5. A new parasitic ciliate, Balantidium honghuensis n. sp., was discovered in the hindgut of R. nigromaculata and R. limnocharis and named after the type locality, Honghu Lake. Its morphology was well described and its 18S rDNA as well as that of B. sinenesis was also sequenced. The result of phylogenetic analysis indicated once more that the genus Balantidium is paraphyly and its phylogenetic position should be lifted to a higher taxon.
6. The morphology, especially the siliverline system of Chilodonella cyprini Moroff, 1902 was described at both light and scanning electron microscopic levels. Phylogenetic analysis was conducted by using 18S rDNA sequences, which contains C. cyprini, C. uncinata, T. stein and other 22 sequences of the class Phyllopharyngea. The result showed that the former three species fell in a single clade and nested within the order Chlamydodontida.|