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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.

Summary Concentrations of rumen ciliate protozoa in 12 Australian red deer ( Cervus elaphus L.) ranged from 15.0 to 50.9 × 10 4 per g. Mean percentage generic distributions were: Entodinium , 83.6; Diplodinium , 3.0; Eudiplodinium , 9.6; Metadinium , 1.9; Elytroplastron , 0.9; Epidinium , 0.4 and Isotricha , 0.5. Twenty species were identified, nine of which represent a new host record. This brings the total number of ciliate species identified in red deer to 32. Most cells of Diplodinium rangiferi were spined, which has not been observed previously. Earlier reports on generic and species composition in red deer are summarized and compared to the present results.

Aims: To study the viability of Diploplastron (Metadinium) affine after its cryopreservation at two cooling rates, and the effect of procedure conditions on viability. Methods and Results: There were differences in viability between cooling rates (1 and 4°C min−1) at 15 or 5°C, but not after thawing. When the equilibrium temperature (25 or 5°C), the cryopreservant (glycerol or dimethyl sulfoxide [DMSO]) and the use of membrane protector were tested, there were no differences caused by the cryopreservant or the membrane protector. However, the equilibrium at 25°C increased the viability (P = 0·005) compared with 5°C. Conclusions: Viability after thawing was 0·10 0·19. Adding the cryopreservant (either glycerol or DMSO) at 25°C instead of 5°C improves viability of D. affine after thawing. Significance and Impact of the Study: Conditions of cryopreservation are largely dependent on the species of rumen protozoa. Number of viable cells after thawing would indicate the possibility of culture recovery for D. affine.

The composition of ciliate protozoa in the rumen of 30 Japanese beef black cattle (Bos taurus taurus) fed in Yoron Island, Kagoshima, was compared with that of 125 Holstein-Friesian cattle (Bos taurus taurus) fed in Hokkaido. Thirteen genera including 44 species with 32 formae detected from Japanese beef black cattle and 15 genera including 48 species with 25 formae from Holstein-Friesian cattle were identified. Thirty-six species with 19 formae were common to both hosts. A new species was recognized from Japanese beef black cattle and named Entodinium yunnense n. sp. This new species was classified into such four formae as yunnense n.f., spinonucleatum n.f., acutonucleatum n.f. and spinolobum n.f. A new forma of Entodinium bifidum having only one caudal spine was also recognized from Japanese beef black cattle and named monospinosum n.f. The average ciliate density in Japanese beef black cattle, 18.7 x 10(4)/ml, was lower than 40.3 x 10(4)/ml in Holstein-Friesian cattle. The average number of ciliate species per head in Japanese beef black cattle, 14.4 was also lower than 17.8 in Holstein-Friesian cattle. The average value of diversity index was 1.789 in Japanese beef black cattle and 1.718 in Holstein-Friesian cattle. Both incidence and composition ratio of Entodinium rectangulatum and E. ovinum were significantly higher in Japanese beef black cattle than in Holstein-Friesian cattle. On the other hand, Charonina ventriculi, E. caudatum, E. rostratum, E. parvum, E. bursa, Metadinium affine and Ostracodinium mammosum showed a reverse relation.

A new species of Metadinium, M. caudatum, closely resembling M. magnum Dogiel, but possessing a scoop-shaped caudal lobe, is described from the rumen contents of Ovibos moschatus collected by Dr. J. S. Tener in the Thelon Game Sanctuary, North West Territories. M. caudatum is the sole species of this genus provided with caudal armature.