Balantidiasis is considered a neglected zoonotic disease with pigs serving as reservoir hosts. However, Balantidium coli has been recorded in many other mammalian species, including primates. Here, we evaluated the genetic diversity of B. coli in non-human primates using two gene markers (SSrDNA and ITS1-5.8SDNA-ITS2). We analyzed 49 isolates of ciliates from fecal samples originating from 11 species of captive and wild primates, domestic pigs and wild boar. The phylogenetic trees were computed using Bayesian inference and Maximum likelihood. Balantidium entozoon from edible frog and Buxtonella sulcata from cattle were included in the analyses as the closest relatives of B. coli, as well as reference sequences of vestibuliferids. The SSrDNA tree showed the same phylogenetic diversification of B. coli at genus level as the tree constructed based on the ITS region. Based on the polymorphism of SSrDNA sequences, the type species of the genus, namely B. entozoon, appeared to be phylogenetically distinct from B. coli. Thus, we propose a new genus Neobalantidium for the homeothermic clade. Moreover, several isolates from both captive and wild primates (excluding great apes) clustered with B. sulcata with high support, suggesting the existence of a new species within this genus. The cysts of Buxtonella and Neobalantidium are morphologically indistinguishable and the presence of Buxtonella-like ciliates in primates opens the question about possible occurrence of these pathogens in humans.

The ciliary (kinetid) structures of the ciliate Strobilidium velox have been examined with scanning and transmission electron microscopes. Somatic kineties consist of a linear row of kinetosomes (monokinetids) and short cilia lying partially beneath a thin fold of cytoplasm. The only fibrillar kinetid structure extending from the kinetosomes is a transverse ribbon of microtubules. The paroral membrane is a single‐file polykinetid possessing a possible transverse ribbon of microtubules and a nematodesma. The oral polykinetids or membranelles are complex, with microtubules extending from both anterior and posterior rows of cilia. While the kinetid structures do not satisfy the criteria for the order Choreotrichida, they are similar to the tintinnids in several other relevant ways. Strobilidium velox is proposed to be an unusual ciliate that is an exception to the concept that somatic kinetids are conservative and reliable phylogenetic indicator structures.

We obtained sequences of the small subunit ribosomal RNA (rRNA) for two new isolates of Balantidium from fishes, Balantidium polyvacuolum and Balantidium ctenopharingodoni. This is the first introduction of molecular data of Balantidium species from fish hosts in the phylogenetic analyses of the ciliate subclass Trichostomatia. Despite the fact that these species share morphological characteristics common to other species of Balantidium, the phylogenetic analysis of their sequences has shown that they are to be placed in a different branch closely related to the so-called Australian clade. Thus, our results indicate that the genus Balantidium is polyphyletic and possibly should be represented by two different genera; however, the analysis of more species from other poikilothermic hosts (amphibians, reptiles) should be made before a revised taxonomical proposal could be made.

SYNOPSIS. Many of the sub‐pellicular and infraciliary structures in protozoa have proved difficult to study with standard thin‐sectioning technics. When these structures are viewed in isolated and fragmented form, many of the thin‐sectioning difficulties are circumvented. Langmuir‐trough isolation followed by critical‐point drying, as well as thin sectioning, were used in this study to determine the patterns of sub‐pellicular microtubules and fibrils interconnecting kinetosomes of membranelles and cirri of Euplotes eurystomus. The fibrillar network in the bases of these ciliary organelles is presented in some detail and apparent variations in pattern are noted. Functional aspects of some of the structures are discussed. With special preparation nearly whole Euplotes may be obtained for study in the electron microscope. Fused cilia were frequently obtained and their ultrastructure was studied.

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The ciliate Vestibulongum corlissi n. g., n. sp. was collected from the intestines of surgeonfish, Acanthurus xanthopterus, in the summer of 1986. In has been examined in the light microscope after protargol staining and by scanning and transmission electron microscopy. Its form is distinct from that of other pycnotrichid ciliates at the generic level. Somatic kinetids were examined; these demonstrate that its cytostome is posterior and that the kinetid structures and the presence of a second transverse microtubular ribbon confirm its placement in the class Litostomatea.

The morphology of Nyctotheroides hubeiensis (Acta Hydrobiol. Sin. 1998, 22(suppl.):187), collected from the rectum of Phelophylax nigromaculatus, is presented in this paper based on detailed morphological information and molecular data. Our phylogenetic analysis showed that N. hubeiensis fell into the Nyctotheroides clade, which was strongly supported as monophyletic and clustered as basal to the genera Nyctotherus and Clevelandella. Also, the monophyly of the Order Clevelandellida and the affinity of parasitic nyctotherids and free-living metopids were indicated in our work. The origin of clevelandellid ciliates as well as their possible evolutionary history was also discussed here; however, the analysis of more species from other vertebrate hosts (fish, reptiles) should be made before a well-supported conclusion can be drawn.

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