Family Ophryoscolecidae

In this spirotrichasin entodiniorid family, there is not more than 1 "dorsal" ("metoral") band of membranelles in addition to the adoral zone. This family contains 18 or more genera which occur in the rumen of ruminants; 13 of these occur in cattle and sheep. The most important genera are Entodinium, Diplodinium, Epidinium and Ophryoscolex. The taxonomy of this group is complicated. Variations in structure, even within a clone, are common in Entodinium and Diplodinium. They make species identification difficult and have served to multiply unduly the number of different species which have been named (Polyansky and Strelkov, 1938; Hungate, 1943; Lubinsky, 1957, 1958).

The body in this family is often flattened, and another source of confusion results from the fact that different authors have used the same name for different sides of the body. Depending on whose terminology was used, every one of the four sides has been called the left, right, dorsal or ventral side. Lubinsky (1958) introduced a new system which has the advantages of eliminating the concept of dorsality and ventrality, which actually has no application in this group, and of making it possible to use the same terms both for Entodinium and for the higher genera in the family. In this system, which is used below, the observer orients the protozoon with its anterior (oral) end pointing away from him (toward 12 o'clock) and with the micronucleus to the left of the macronucleus (toward 9 o'clock). The sides are then designated left (the observer's left, i.e., the micronuclear side), right, upper and lower.

If this terminology is accepted, then the term, dorsal zone of membranelles (DZM), which is used in describing ophryoscolecids, is no longer appropriate. Lubinsky used "metoral membranelle zone" instead.

Genus Ophryoscolex

The body is ovoid, with adoral and metoral zones of membranelles. The metoral zone is some distance from the anterior end and encircles 3/4 of the body circumference at its middle, being broken on the upper right side. There are 3 skeletal plates extending the length of the body on the upper right side, and 9 to 15 contractile vacuoles arranged in an anterior and a posterior circle. The macronucleus is simple and elongate. This genus occurs in the rumen and reticulum of cattle, sheep, goats and wild sheep. It is not common, and is seldom present in large numbers when it does occur, but is interesting because of its size and appearance.

Ophryoscolex inermis Stein, 1858 occurs principally in the goat. It measures 170 to 190 by 65 to 100 u. Becker and Talbott (1927) found it in 1 of 26 cows in Iowa. It differs from the other species of Ophryoscolex in having a rounded posterior end, without spines.

O. purkinjei Stein, 1858 occurs in cattle. It measures 200 by 80 u and has 1 or 3 terraces of thorn-like appendages or spines encircling the posterior end of the body except for a short gap on the right side; in addition, there is a bifid spine at the posterior end. Becker and Talbott (1927) did not find this species in Iowa cattle.

O. caudatus Eberlein, 1895 occurs in sheep and cattle. It resembles Q. purkinjei but its terminal spine is long and not bifid. Becker and Talbott (1927) found it in 1 of 26 cattle in Iowa.

Genus Entodinium

The body is truncate anteriorly, with the adoral zone of membranelles at that end. There is no metoral zone of membranelles, and skeletal plates are likewise absent. The contractile vacuole is anterior. The macronucleus is cylindrical or sausage-shaped and dorsal. The micronucleus is anterior to the middle on the upper left side of the macronucleus. This is one of the commonest and most important genera in the rumen and reticulum of cattle, sheep, goats and other ruminants.

Many species of Entodinium have been named, but knowledge of the true number and of their correct names awaits some future exhaustive taxonomic study. In the earlier papers, great reliance was placed on caudal spination to differentiate species, but later it was found that this character varies within a species. Thus, E. caudatum was given its name because it has a long posterior spine on the right side in addition to 2 short, pointed lobes on the left. A second species, E. lobosospinosum, received its name because it has only a single lobe on the left (the upper one) in addition to the spine on the right. A third species, E. dubardi, has no posterior spines or lobes at all. However, it was later found that the caudal spination varies all the way from the caudatum type to the dubardi type in several species, and that other characters are more constant and more valuable in differentiating species.

Six types or classes of caudal spination have been set off along this series for E. caudatum. Three of them have received special names, and workers now speak of E. caudatum forma caudatum, E. caudatum forma lobospinosum, and E. caudatum forma dubardi, the last being a form without a tail at all! These same forma names are also used for E. simulans, and some of them for E. rectangulatum and E. lobospinosum (cf. Poljansky and Strelkow, 1938; Lubinsky, 1957).

Entodinium bursa Stein, 1858 has a flattened body which measures about 80 by 60 u. (Because of the variation in caudal spination, measurements of Entodinium are made nowadays from the anterior end to the cytopyge, but early workers usually gave measurements to the end of the caudal spine.) The sausage-shaped macronucleus is 4/5 of the body length, and the micronucleus is pressed closely to it. The body surface has conspicuous longitudinal striations. The contractile vacuole is anterior.

E. minimum Schuberg, 1888 has a flattened body which measures about 40 by 22 u. The right margin of the body is strongly convex and the left margin almost straight. The body surface has faint longitudinal striations. The macronucleus is about 1/3 of the body length. The contractile vacuole is anterior.

E. caudatum Stein, 1858 has a flattened body about 30 to over 80 u long. The macronucleus is about half of the body length; it is broader anteriorly than posteriorly. The contractile vacuole is near the anterior end of the macronucleus. The upper side of the body is hollowed out to form a groove which broadens posteriorly. As mentioned above, there is great variation in the caudal spination.

E. bicarinatum Cunha, 1914 may be a synonym of E. caudatum. It measures about 61 by 35 u, and the upper groove is not as deep as in E. caudatum.

E. furca Cunha, 1914, too, may be a synonym of E. caudatum. It has 2 unequal caudal projections, 1 on the left and the other on the right, and measures about 52 by 27 u.

E. dentatum Stein, 1859 measures 60 to 90 by 30 to 50 u and has 6 incurved, tooth-like posterior projections.

E. rectangulatum Kofoid and Mac-Lennan, 1930 measures 23 to 47 by 23 to 39 u. Its body is nearly rectangular as seen from above, except for the caudal spines. The macronucleus is about half the body length and is broader anteriorly than posteriorly. The contractile vacuole is about the middle of the body at the level of the esophagus, i.e., more to the left than that of E. caudatum. The upper groove is more marked than that of E. caudatum, and its anterior end separates the contractile vacuole from the macronucleus.

E. lobosospinosum Dogiel, 1927 measures 18 to 33 by 13 to 25 u. Its body is rectangular as seen from above. The macronucleus is about half the body length. The contractile vacuole is on the mid-line of the upper side of the body on the level of the micronucleus and to the left of the broad upper groove.

E. simulans Lubinsky, 1957 measures 27 to 44 by 21 to 34 u. Its body is ovoid as seen from above. The macronucleus is about half the body length. The contractile vacuole is on the mid-line of the upper side of the body at the level of the micronucleus and to the left of the upper groove. This groove is narrow and long, with a slit-shaped anterior half.

E. longinucleatum Dogiel, 1925 measures 39 to 64 by 27 to 46 u and has an ellipsoidal, flattened body. The macronucleus usually extends the whole length of the body from the anterior end to the cytopyge. The contractile vacuole is close to the upper side of the macronucleus, slightly anterior to the micronucleus.

E. rostratum Fiorentini, 1889 measures 27 to 51 by 13 to 23 u and has a rather long, slim, flattened body with a strongly convex right side and a concave left side. The macronucleus is narrow, bandlike, and about half the length of the body. The contractile vacuole is directly anterior to the macronucleus.

E. laterale Kofoid and MacLennan, 1930 measures 19 to 28 by 18 to 21 u and has a short, fairly broad, truncated ellipsoidal, flattened body. The macronucleus is broad and wedge-shaped, less than half the length of the body, and lies in the anterior half of the body. The contractile vacuole is in the middle of the upper side.

E. nanellum Dogiel, 1922 measures 20 to 32 by 10 to 18 u and has an ovoid, flattened body. The macronucleus is thin, wedge-shaped, and longer than half the body length. The contractile vacuole is above the anterior end of the macronucleus.

E. bimastus Dogiel, 1927 measures 30 to 46 by 28 to 40 u and has a subspherical, flattened body. The macronucleus is flattened, wedge-shaped, and about 2/3 of the length of the body. The contractile vacuole is above the anterior end of the macronucleus.

E. exiguum Dogiel, 1925 measures 21 to 29 by 14 to 18 u and has an elongate, oval body. The macronucleus is relatively short and thick, being shorter than half the body length, and lies in the middle of the body.

E. dubardi Buisson, 1923 (syn., E. simplex Dogiel, 1925 pro parte; the true E. simplex occurs in the reindeer) measures 30 to 50 by 20 to 29 u and has an oval or elongate oval, flattened body. The macronucleus is more or less band-shaped, with a somewhat broader anterior end. It is about half as long as the body and lies anteriorly in it. The contractile vacuole is below the anterior end of the macronucleus.

E. vorax Dogiel, 1925 measures 60 to 121 by 40 to 83 u and has an oval, plump, thick body. The anterior end is often smaller than the posterior. The macronucleus is sausage-shaped, about half as long as the body, and lies in the anterior part of the body. The contractile vacuole is to the right of the anterior end of the macronucleus.

Quite a few other species of Entodinium have been described from various ruminants. Among them are the following, which Kofoid and MacLennan (1930) described from the zebu: E. ellipsoideum, E. acutonucleatum, E. pisciculum, E. biconcavum, E. bifidum (Dogiel) E. acutum, E. aculeatum, E. brevispinum, E. laterospinum, E. ovoideum, E. rhomboideum, E. gibberosum, E. tricostatum, and E. indicum.

Genus Epidinium

The body is elongate and twisted around its main axis. The adoral zone of membranelles is at the anterior end, and the metoral zone elsewhere. There are 3 skeletal plates with secondary plates. The macronucleus is simple and club-shaped. There are 2 contractile vacuoles. This genus occurs in the rumen and reticulum of cattle, sheep, goats, camels, reindeer, elk, and other ruminants.

Epidinium ecaudatum (Fiorentini, 1889) (syn., Diplodinium ecaudatum) measures 82 to 173 by 36 to 70 u and has an elongate body with a convex left side and a flat or slightly concave right side. This species has 9 formae which differ principally in their caudal spination: E. ecaudatum forma ecaudatum has no caudal spines, forma caudatum has a single long spine and the posterior end of its body is narrow, hamatum has a single long spine and the posterior end of its body is broad, bulbiferum has a bulb-shaped appendage instead of a spine, bicaudatum has 2 spines, tricaudatum has 3, quadricaudatum has 4, catteneoi has 5 short ones, and fasciculus has 5 very long ones with greatly swollen bases. All 9 formae occur in the rumen of cattle, the most common being ecaudatum and caudatum. Ecaudatum, hamatum and cattaneoi are found in sheep, and the last in goats as well. Ecaudatum and caudatum also occur in the reindeer, caudatum and hamatum in camels and caudatum in the elk.

Genus Eodinium

The metoral zone of membranelles is at the same level as the adoral zone. Skeletal plates are absent. The macronucleus is a straight, rod-like body near the left edge. Two contractile vacuoles are present. This genus occurs in the rumen and reticulum of cattle and sheep.

E. posterovesiculatum (Dogiel, 1927) Kofoid and MacLennan, 1932 measures 47 to 60 by 23 to 30 u and has a relatively long, flattened body with rounded ends. The macronucleus is very long, straight, and has 2 deep depressions on its left side. The micronucleus lies in the posterior one, and a contractile vacuole in the anterior one. The second contractile vacuole is posterior to the macronucleus. This species occurs in cattle.

E. bilobosum (Dogiel, 1927) Kofoid and MacLennan, 1932 measures 46 to 60 by 30 to 44 u and has a relatively short, flattened body with 2 caudal spines, 1 dorsal and the other ventral. The nuclei and vacuoles are similar to those of E. posterovesiculatum. This species occurs in cattle and sheep.

Eodinium lobatum Kofoid and Mac-Lennan, 1932 measures 44 to 60 by 29 to 37 u and has a narrow body. The macronucleus is narrow and rod-like, and is almost as long as the body. It has 3 large depressions in its left side; the micronucleus lies in the middle one, and the contractile vacuoles in the end ones. This species occurs in the zebu.

Genus Diplodinium

The metoral zone of membranelles is on the same level as the adoral zone. Skeletal plates are absent. The macronucleus is beneath the upper surface of the body; its anterior third is bent to the right at an angle of 30 to 90°. Two contractile vacuoles are present. This genus occurs in the rumen and reticulum of cattle, goats, sheep, camels, reindeer and various wild ruminants.

In this genus, as in Entodinium, there is also considerable variation in the caudal spination.

Diplodinium dentatum (Stein, 1858) Schuberg, 1888 measures 55 to 82 by 44 to 62 u. Its body has a broad, truncate posterior end with 6 large, relatively heavy, incurved caudal spines. The left side is convex and the right one concave. The macronucleus is 25 to 50 u long; it is heavy and rod-like, with the anterior end bent at a 45° angle. The 2 contractile vacuoles lie in the left rib slightly below the midline. This species occurs in the ox and zebu.

D. quinquecaudatum Dogiel, 1925 measures 57 to 73 by 47 to 65 u. It resembles D. dentatum, but has 5 caudal spines. It occurs in cattle and sheep.

D. anacanthum Dogiel, 1927 measures 60 to 124 by 38 to 72 u. The posterior end of its body tapers, giving it a somewhat conical appearance. The macronucleus varies a good deal in length. Its anterior third is bent at an angle of about 45°. The 2 contractile vacuoles are on the lower side. This species has 7 formae (which Kofoid and MacLennan, 1930, considered separate species): anacanthum, monacanthum, diacanthum, triacanthum, tetracanthum, pentacanthum, and anisacanthum, with 0, 1, 2, 3, 4, 5 and 6 caudal spines, respectively. It occurs in the ox and zebu.

Ciliates of ruminants

D. psittaceum Dogiel, 1927 measures 95 to 155 by 59 to 105 u and has a heavy, rounded, posteriorly tapering body with a thin ventral spine on the right and a narrow flange on the left of the posterior third of the body. The macronucleus is a stout rod-like body with its anterior end bent at a 40° angle. The contractile vacuoles lie near the left side. This species occurs in the ox and zebu.

D. bubalidis Dogiel, 1925 measures 104 to 195 by 58 to 98 u and has an oval body with its largest diameter anterior, a strongly convex left side and a slightly convex right one. There is a small, longitudinal groove on the posterior part of the upper surface of the body, and a single, thin spine on the right. This species occurs in cattle and African antelope.

D. elongatum Dogiel, 1927 measures 177 to 205 by 73 to 100 u and has an elongate body with weakly convex left and right sides and a narrow groove in the posterior end of the upper surface of the body. It occurs in the ox.

D. laeve Dogiel, 1927 measures 77 to 100 by 52 to 70 u and has a roughly triangular body with no caudal projections except a small lobe on the right. It occurs in goats.

D. cristagalli Dogiel, 1927 measures 77 to 100 by 52 to 70 u and has a triangular body with the lower side extended posteriorly to form a prominent fan with 2 to 7 spines. It occurs in goats.

D. flabellum Kofoid and MacLennan, 1932 measures 82 to 118 by 57 to 82 u and has a roughly triangular body with the upper side extended posteriorly to form a prominent fan with 5 to 7 spines, and with 2 small spines on the posterior left side. It occurs in the zebu.

Genus Eremoplastron

The metoral and adoral zones of membranelles are at the same level. There is a single, narrow skeletal plate beneath the upper surface. The macronucleus is triangular or rod-like, often with its anterior end bent to the right. Two contractile vacuoles are present. This genus occurs in the rumen and reticulum of cattle, sheep, antelope and reindeer.

Eremoplastron rostratum (Fiorentini, 1889) Kofoid and MacLennan, 1932 (syn., Diplodinium helseri Becker and Talbott, 1927) measures 40 to 63 by 22 to 47 u and has a proportionately long, compressed body with a thick flange on the left and a large caudal spine on the right. The macronucleus is rod-like. This species occurs in the ox and zebu.

E. neglectum (Dogiel, 1925) is 81 to 124 u long and has an elongate oval body with the left side strongly convex, the right side slightly convex, a large lobe on the right, and a long, rod-like macronucleus. It occurs in cattle and African antelope.

E. bovis (Dogiel, 1927) (syn., Diplodinium clevelandi Becker and Talbott, 1927) measures 52 to 100 by 36 to 57 u and has an ellipsoidal, compressed body with a somewhat flattened right side, a more strongly convex left side, and a small caudal lobe. The macronucleus is rod-shaped. This species occurs in the ox, zebu and sheep.

E. monolobum (Dogiel, 1927) is 58 to 83 u long and has a nearly spherical body with a prominent right lobe and a low, blunt left lobe. The macronucleus is thick and rod-shaped. This species occurs in cattle.

E. dilobum (Dogiel, 1927) is 73 to 101 u long and has an ellipsoidal, flattened body with 1 left and 1 right caudal lobe. The macronucleus is rod-shaped. This species occurs in cattle and sheep.

E. rugosum (Dogiel, 1927) is 69 to 90 u long and has a short body with a flat or slightly concave right side, a convex left side,, and a deep cuticular fold from the cytopyge along the left side of the macronucleus to the region of the metoral zone of membranelles. The right lobe is laterally compressed, with.8 to 10 shallow indentations in its left border. The macronucleus is long and rod-like. This species occurs in cattle.

E. brevispinum Kofoid and MacLennan, 1932 measures 72 to 92 by 42 to 53 u and has an ellipsoidal, flattened body with 2 short caudal spines. The macronucleus is rod-shaped. This species occurs in the zebu.

E. magnodentatum Kofoid and MacLennan, 1932 measures 58 to 82 by 30 to 50 u and has a rectangular, flattened body with a large, compressed caudal spine on the right and a similar caudal spine on the left. The macronucleus is rod-shaped. This species occurs in the zebu.

Genus Eudiplodinium

The metoral and adoral zones of membranelles are at the anterior end. There is a single, narrow skeletal plate beneath the upper surface. The macronucleus is rod-like, with its anterior end enlarged to form a hook which opens to the left. The pellicle and ectoplasm are thick. There are 2 contractile vacuoles with heavy membranes and prominent pores.

Eudiplodinium maggii (Fiorentini, 1889) measures 104 to 240 by 63 to 77 u and has a roughly triangular body with a smoothly rounded posterior end. It occurs in the rumen and reticulum of the ox and zebu.

Genus Diploplastron

The metoral and adoral zones of membranelles are at the anterior end. There are 2 skeletal plates beneath the upper surface. The macronucleus is narrow and rod-like. There are 2 contractile vacuoles below the left surface, separated from the macronucleus.

Diploplastron affine (Dogiel and Fedorowa, 1925) measures 88 to 120 by 47 to 65 u and is more or less ellipsoidal. It occurs in the rumen of cattle, sheep and goats.

Genus Metadinium

The metoral and adoral zones of membranelles are at the anterior end. There are 2 skeletal plates beneath the upper surface which are sometimes fused posteriorly. The macronucleus has 2 to 3 left lobes. There are 2 contractile vacuoles. The pellicle and ectoplasm are thick. There are conspicuous esophageal fibrils beneath the left and upper sides.

Metadinium medium Awerinzew and Mutofowa, 1914 measures 180 to 272 by 92 to 170 u and has a heavy body with large membranelle zones. The skeletal plates are narrow. This species occurs in the rumen of the ox and zebu.

M. tauricum (Dogiel and Fedorowa, 1925) measures 185 to 288 by 70 to 160 u and has a heavy body. The skeletal plates are fused posteriorly. The anterior and median lobes of the macronucleus are large, and the posterior lobe is small. This species occurs in the rumen of sheep, goats and cattle.

M. ypsilon (Dogiel, 1925) measures 110 to 152 by 60 to 72 u and has an oval, flattened body with a rounded posterior end. The anterior lobe of the macronucleus is small, and there is no posterior lobe. The skeletal plates are fused posteriorly. This species occurs in the rumen of cattle.

Genus Polyplastron

The metoral and adoral zones of membranelles are at the anterior end. There are 2 separate or fused skeletal plates beneath the upper surface, and 3 longitudinal plates with anterior ends connected by cross bars beneath the lower surface. There is a longitudinal row of contractile vacuoles beneath the left surface, and others in other locations.

Polyplastron multivesiculatum (Dogiel and Fedorowa, 1925) measures 120 to 190 by 78 to 140 u and has an oval body with a smoothly rounded posterior end. There is a row of 4 contractile vacuoles near the macronucleus, plus 2 beneath the left surface, 1 beneath the right surface and 2 beneath the upper surface. The 2 upper skeletal plates are separate. This species occurs in the rumen of cattle and sheep.

P. fenestratum Dogiel, 1927 resembles P. multivesiculatum except that the upper skeletal plates are partly fused. This species occurs in the rumen of cattle.

P. monoscutum Kofoid and MacLennan, 1932 resembles P. multivesiculatum except that the upper skeletal plates are completely fused to form a single broad plate. This species occurs in the rumen of cattle.

Genus Elytroplastron

The metoral and adoral zones of membranelles are at the anterior end. There are 2 skeletal plates beneath the upper surface, a small plate beneath the right surface and a long plate below the lower surface. The pellicle and ectoplasm are thick. There are conspicuous fibrils beneath the left and upper surfaces.

Elytroplastron bubali (Dogiel, 1928) measures 110 to 160 by 67 to 97 u and has an ellipsoidal body with a smoothly rounded posterior end. There are 4 contractile vacuoles along the left midline. This species occurs in the rumen of the water buffalo and zebu.

Genus Ostracodinium

The metoral and adoral zones of membranelles are at the anterior end. There is a broad skeletal plate beneath the upper side of the body, and a row of 2 to 6 contractile vacuoles beneath the left surface. Heavy pharyngeal fibrils are present which extend to the posterior end.

Ostracodinium mammosum (Railliet, 1890) measures 41 to 110 by 25 to 68 u and has a left caudal lobe and a right lobe which is hollow on the left side. The posterior part of the skeleton extends only 2/3 of the way across the upper side. The macronucleus has a large, shallow depression in the middle of its lower side. There are 3 contractile vacuoles. This species occurs in the rumen of the ox and zebu.

O. gracile (Dogiel, 1925) measures 90 to 133 by 42 to 60 u and has a roughly triangular body with flat right and lower surfaces and convex left and upper surfaces, and with a smoothly rounded posterior end. The skeletal plate extends across the upper surface. The macronucleus has 2 lobes. There are 2 contractile vacuoles. This species occurs in the rumen of the ox, zebu, sheep and African antelopes.

O. tenue (Dogiel, 1925) measures 59 to 76 by 28 to 38 u and has a slender body with a smoothly rounded posterior end. The skeletal plate extends across the upper surface. The macronucleus has an anterior and a median left lobe. There are 2 contractile vacuoles. This species occurs in the rumen of cattle and an African antelope.

O. trivesiculatum Kofoid and Mac-Lennan, 1932 measures 78 to 100 by 42 to 60 u and has a triangular body with a smoothly rounded posterior end. The skeletal plate extends across the upper side. The macronucleus has a small, shallow depression in the middle of the lower side. There are 3 contractile vacuoles. This species occurs in the rumen of the zebu.

O. quadrivesiculatum Kofoid and Mac-Lennan, 1932 measures 92 to 112 by 43 to 56 u and has a triangular body with a bluntly rounded posterior end. The skeletal plate extends across the upper side. The macronucleus is elongate and rodlike. There are 4 contractile vacuoles. This species occurs in the rumen of the zebu.

O. nanum (Dogiel, 1925) measures 47 to 70 by 30 to 41 u and has an ellipsoidal body with a slender, right caudal spine. The skeletal plate extends between the macronucleus and the ventral surface. The macronucleus is short and stout. There are 2 small contractile vacuoles. This species occurs in the rumen of cattle and African antelopes.

O. gladiator (Dogiel, 1925) measures 78 to 112 by 40 to 55 u and has a slender body with a long, very narrow, right caudal spine. The skeletal plate extends between the macronucleus and the right side. The macronucleus has a lobe on the left anterior end. There are 2 contractile vacuoles. This species occurs in the rumen of cattle and African antelopes.

O. crassum (Dogiel, 1925) measures 120 to 142 by 80 to 100 u and has a heavy body with a smoothly rounded posterior end. The skeletal plate extends under only 1/2 of the upper side. The macronucleus is short and stout, with a wide, shallow depression in the anterior half of its left side. There are 2 contractile vacuoles. This species occurs in the rumen of cattle and the steenbock.

O. obtusum (Dogiel and Fedorowa, 1925) (syn., Diplodinium hegneri Becker and Talbott, 1927) measures 118 to 148 by 55 to 80 u and has an ellipsoidal, only slightly flattened body, with a smoothly rounded posterior end. The posterior part of the skeleton extends across only 2/3 of the upper side. The macronucleus is elongate and rod-like. There are 6 contractile vacuoles. This species occurs in the rumen of cattle and reindeer.

O. venustum Kofoid and MacLennan, 1932 measures 76 to 115 by 41 to 60 u and has a triangular body with a small posterior right lobe. The skeletal plate extends beneath the upper surface between the macronucleus and the right side. The macronucleus has 2 left lobes. There are 2 contractile vacuoles. This species occurs in the rumen of the zebu.

O. dogieli Kofoid and MacLennan, 1932 measures 92 to 130 by 48 to 63 u and has an ellipsoidal body with a strongly convex left side, a slightly convex right side and a flattened right lobe lying below the cytopyge. The skeletal plate extends between the macronucleus and the right side. The macronucleus has 2 left lobes (1 anterior and 1 median). There are 2 contractile vacuoles. This species occurs in the rumen of the ox.

O. clipeolum Kofoid and MacLennan, 1932 measures 92 to 128 by 50 to 65 u and has an ellipsoidal body with a flattened lobe projecting from the right posterior surface below the midline. The skeletal plate extends beneath the upper surface between the macronucleus and the right side. The macronucleus has 2 left lobes. There are 3 contractile vacuoles. This species occurs in the rumen of the zebu.

O. monolobum Dogiel, 1927 measures 105 to 150 by 55 to 77 u and has a rectangular body with a large right lobe. The skeletal plate extends under only 2/3 of the left side. The macronucleus is elongate and rod-like. There are 5 contractile vacuoles. This species occurs in the rumen of the ox.

O. dilobum Dogiel, 1927 measures 88 to 140 by 54 to 78 u and has an ellipsoidal body with a laterally flattened right lobe and a flattened left lobe. The skeletal plate extends under only 2/3 of the left side. The macronucleus is elongate and rod-like. There are 5 contractile vacuoles. This species occurs in the rumen of cattle.

O. rugoloricatum Kofoid and MacLennan, 1932 measures 84 to 125 by 37 to 58 u and has a rectangular body with a flattened right lobe. The left side of the exceptionally large skeletal plate turns in and extends toward the middle of the body. The macronucleus is straight and rod-like. There are 3 contractile vacuoles. This species occurs in the rumen of the zebu.

Genus Enoploplastron

The metoral and adoral zones of membranelles are near the anterior end. There are 3 separate or partially fused skeletal plates beneath the upper and right surfaces of the body. There are 2 contractile vacuoles. The pharyngeal fibrils are heavy.

Enoploplastron triloricatum (Dogiel, 1925) measures 60 to 112 by 37 to 70 u and has an ellipsoidal body with a smoothly rounded posterior end. The skeletal plates are separate. The macronucleus has a shallow depression in the anterior half of its left side. This species occurs in the rumen of the ox, reindeer and an African antelope.