This review presents the principal methods used in taxonomic studies of rumen ciliates: live observation, Lugol staining, fixation and staining with methyl-green formalin saline (MFS) solution, protargol staining, silver carbonate impregnation, scanning electron microscopy and molecular techniques. Mastering these techniques is essential for successful research on the taxonomy of rumen ciliates. No single technique reveals all of the characteristics required for a complete description of a rumen ciliate; therefore, it is necessary to combine the use of these techniques as appropriate to the rumen ciliate group under study. Tables are provided to summarize: 1) morphological methods more appropriate for revealing morphological structures of interest, 2) morphological methods indicated for each group of rumen ciliates, and 3) main primers used for PCR amplification of the 18S rDNA of rumen ciliates.

The species composition, prevalence, and average relative abundance of rumen ciliates were analyzed in 16 Brazilian sheep. 28 species of ciliates were identified belonging to 3 families: Isotrichidae, Ophryoscolecidae, and Parentodiniidae. Among these ciliates, Entodinium alces, Metadinium esalqum, and M. rotundatum were found for the first time in sheep, and other 12 species for the first time in Brazilian sheep. Different morphotypes of parentodiniid ciliates were identified in 7 of the 16 sheep analyzed and this is the second report of this family in ruminants. The species Entodinium contractum was redescribed based on the new data on the general morphological features; for the first time, we described the oral infraciliature, which in this species is of the Entodinium-type. In this species, it is noteworthy that the prominent vestibular polybrachykinety can be used as an important identifying characteristic.

Polymorphism and inconsistencies in the taxonomy of Diplodinium anisacanthum da Cunha, 1914 (Ciliophora, Entodiniomorphida, Ophryoscolecidae) and taxonomic notes on the genus Diplodinium Schuberg, 1888

To date the genus Diploplastron comprised only one species of ophryoscolecid ciliate, Diploplastron affine, which is characterized by having two retractable ciliary zones in the anterior end of the body, two slender and juxtaposed skeletal plates on the right side, a rod shape macronucleus, and two contractile vacuoles. During study on the characterization of rumen ciliate community composition in Brazilian domestic sheep, we observed ciliates with atypical morphology but with diagnostic features of genus Diploplastron. This study describes Diploplastron dehorityi, a new species of ophryoscolecid ciliate, that differs from D. affine, primarily, in the morphology of skeletal plates, morphology of nuclear apparatus and body shape. In addition to the similarities between the new species and congener species, D. dehorityi has some morphological similarities to species of genus Eremoplastron.

The genus Metadinium includes ophryoscolecid ciliates, with two retractile ciliary zones in the anterior body portion, two broad skeletal plates, a lobed macronucleus and two contractile vacuoles. Species belonging to this genus were recorded in several geographical locations and in different host species. However, they were mostly described based on a single ciliatological technique, and until now, there is only one description of the infraciliary pattern in Metadinium ciliates (Metadinium medium). The present study performs the morphological and infraciliature characterization of four species belonging to Metadinium: M. esalqum, M. minorum, M. rotundatum and M. ypsilon; and presents taxonomic notes on the genus. The oral infraciliature in these four Metadinium species corresponds to the Diplodinium-type, pattern shared with genera Diplodinium, Diploplastron, Eudiplodinium, Eremoplastron and Polyplastron. A brief review conducted highlights the difficulty of delimiting Metadinium species due to the morphological similarity among them.