Didinium Stein, 1859 (ref. ID; 2013) or 1867 (ref. ID; 3540, 3596)
Synonym; Monodinium (Fabre-Domergue) (ref. ID; 1618)

[ref. ID; 2013]
Body barrel-shaped with short cone-shaped snout protruding from flattened anterior region, posterior broadly rounded. Oral aperture not permanent, forms only when ingesting prey which is typically Paramecium; then the feeding oral aperture becomes highly expandable. Body ciliation reduced to 2 narrow bands of closely-set cilia which encircle the body transversely. The anterior band is located at the shoulder region where the snout joins the body. The posterior ciliary band is just behind the body mid-line. Each ciliary band is composed of numerous short rows of cilia and their kinetosomes are arranged diagonally to the major body axis. The rest of the body is devoid of cilia except behind each ciliary band, where there are 4 to 6 longitudinal rows of clubbed cilia, which are easily visible but may be shown by silver impregnation methods or electron microscopy. Macronucleus sausage to horse-shoe shape. Contractile vacuole posterior.
Quote; Colin R. Curds "British and other freshwater ciliated protozoa Part I Ciliophora: Kinetofragminophora" Cambridge University Press, 1982 (ref. ID; 2013)

[ref. ID; 3596]
Body ovate, anteriorly produced to make a conical process bearing a mouth at the tip, with one, two or more ciliary girdles; pharynx elongate, conspicuous; macronucleus arched rod-shaped; contractile vacuole terminal. (ref. ID; 3596)

Didinium balbianii Fabre-Domergue, 1888 (ref. ID; 1619, 3115, 3540) reported year? (ref. ID; 1618, 3596) reported author and year? (ref. ID; 3292)
Syn; Monodinium balbianii Fabre-Domergue, 1888 (ref. ID; 3115)
Description; A single girdle of pectinelles near anterior end; fresh water. (ref. ID; 1618)
Body oval with a single ciliary band, 1.4 of the greatest transdiameter in length; contractile vacuole posterior, single or more. (ref. ID; 3596)
Comments; The species differs from D. gargantua Meunier in its smaller size and in possessing a single ciliary and instead of two. (ref. ID; 3596)
Measurements; 60-100 um long. (ref. ID; 1618)
Length 60-96 um. (ref. ID; 3596)
Didinium balbianii var. nanum Kahl, 1930 (ref. ID; 3540 original paper, 3544) reported year? (ref. ID; 3491) reported author and year? (ref. ID; 1619, 3292)
Description; The variety is similar to Didinium gargantum Meunier in general contour, but it is easily distinguished in having a single ciliary band, and it is different from the typical form of D. balbianii (Fabre-Domerque) in smaller size and in having a ciliary band composed of coarse longer cilia. (ref. ID; 3544)
Measurements; Length 24-25; breadth 12-25 um. (ref. ID; 3544)
Didinium gargantua Meunier, 1907 (ref. ID; 1619, 3540) or 1910 (ref. ID; 3596), gargantum Meunier (ref. ID; 3544)
Description; The globular body with a conical proboscis has two ciliary bands. (ref. ID; 3544)
Body round, 1.2 of the greatest transdiameter of the body in length; proboscis conical (40 degrees), its length 0.26 of the total length; anterior ciliary band on the shoulder and the posterior near the aboral region. (ref. ID; 3596)
Comments; The species differs from D. nasutum (O. F. Muller) in showing a stouter contour and in the aboral ciliary girdle situated more posterior in position. This marine species is discriminated from the oldest species, D. nasutum which occurs in fresh and brackish waters, in a more round body shape and in a lower position of the posterior ciliary band which is located near the middle part of the body in D. nasutum. In living specimens the proboscis extends to form a high cone, while that of fixed ones shows only a low rounded elevation. (ref. ID; 3596)
Measurements; Length 40-95; breadth 25-72 um. (ref. ID; 3544)
Length 150-160; breadth 125-128 um. (ref. ID; 3596)
Didinium nasutum O. F. Muller, 1786 (ref. ID; 1219, 1308, 1335, 1619, 1629, 2245, 2573, 3115, 3540) reported year? (ref. ID; 1618) or (Mueller, 1773) Stein, 1859 (ref. ID; 4488, 4612, 4613) reported author and year? (ref. ID; 191, 3292, 4407)
Syn; Chytridium steini Eberhard, 1862 (ref. ID; 3115); Vorticella nasuta O. F. Muller, 1773 (ref. ID; 4612, 4613) or 1786 (ref. ID; 3115)
Description; Barrel-shaped; highly granulated endoplasm (sometimes nearly black); 2 girdles of special cilia that are used only for very rapid locomotion; a group of short bristles is located behind each girdle of cilia ("sensory bristles" consisting of about 4-6 short rows of modified cilia). The mouth at the tip of a conspicuous proboscis is highly protrusible and supported by long trichites; macronucleus horseshoe-shaped; contractile vacuole terminal. (ref. ID; 1219)
[Ultrastructure] Didinium nasutum is a familiar ciliate with an everted cytopharynx (proboscis), cilia in short rows forming two girdles around the cell, and a brush (= brosse) immediately posterior to each girdle. (ref. ID; 4407)
(The cilia of the girdles) Each row of cilia is oblique to the long axis of the cell and lies within a shallow furrow. The rows in both girdles consist of two to three pairs of kinetosomes followed posteriorly by several single kinetosomes. The single kinetosomes in both girdles are identical and are homologous to the somatic cilia of other haptorian ciliates. These are ciliated and have three types of infraciliary fibers (the postciliary and transverse microtubules and a kinetodesmal fiber). The postciliary ribbon of five to seven microtubules arises adjacent to kinetosomal triplet 9. In transverse sections through the kinetosome, the angle of this ribbon is convergent (i.e. the postciliary angle is < 90 degrees to the kinety axis (Williams & Frankel, 1973)). As the postciliary microtubules extend up toward the cell surface, the microtubules bunch together forming double-row stacks. At the cell surface, the microtubules curve posteriorly and continue in stacks under the alveolar membranes. The microtubules extend for several microns and overlap with the postciliary microtubules from other kinetosomes in the kinety. At the posterior end of the girdles, the postciliary microtubules continue under the alveolar membrane of the nonciliated parts of the cell overlapping with the postciliary microtubules from the barren kinetosomes found there. There are two transverse microtubular ribbons. The fist ribbon of six to seven microtubules originates adjacent to kinetosomal triplets 3, 4, and 5. These microtubules, along with a layer of electron-dense material, extend anterolaterally up to the cell surface. One of the microtubules and the electron-dense material also continue from the proximal end of the kinetosome into the cell. As it passes through the tela corticalis, the electron-dense material shows a periodicity of approximately 50 nm. It also forms a cylinder with the microtubule embedded in the anterior wall. The microtubule and electron-dense material end after they pass the boundary of the tela corticalis and have penetrated the endoplasm. The second transverse ribbon of two to three microtubules originates near kinetosomal triplet 5 at an angle to the first so that it is difficult to see both in the same section. This second ribbon runs laterally and to the left where it ends near the cell surface. The kinetodesmal fiber originates on triplets 6 and 7. It extends from the kinetosome laterally to the cell's right. As the kinetodesmal fiber moves away from the kinetosome, it projects anteriorly and toward the cell surface, passes below other overlapping postciliary microtubules, and ends before it meets with the kinety to the right. All of the ciliated kinetosomes in a row are close together and joined at their proximal ends by an electron-dense band. This connecting material is similar to that described for Monodinium (Rodrigues de Santa Rosa & Didier, 1975): the proximal end of each kinetosome is surrounded by electron-dense material; the material from adjacent kinetosomes is separated by a small strip that lies perpendicular to the axis of the kinety. Although these kinetosomes are packed closely together, they cannot be considered organized somatic kinetosomes (Foissner & Foissner 1988, Lipscomb & Riordan 1990), because none of them contribute transverse microtubules to the support of the cytopharynx (proboscis), their kinetodesmal fibers do not overlap, and none of them have nematodesmata-like bundles of microtubules originating from their base. There are predominately two but occasionally three pairs of kinetosomes at the anterior ends of the ciliary rows in both the anterior and posterior girdles. These are comparable to the similarly positioned pairs described in Monodinium (Rodrigues de Santa Rosa & Didier, 1975) and both are homologous to the oral dikinetids of other haptorian ciliates. In both girdles, the ciliated kinetosome of each pair has postciliary and two sets of transverse microtubules. The nonciliated kinetosome has a curving transverse ribbon of seven to 14 microtubules, a single postciliary microtubule, and a nematodesma. In the anterior girdle, the nematodesmata from the nonciliated kinetosome extend through the tela corticalis and form the outer supporting structure of the oral apparatus. Often, at the tela corticalis/endoplasm boundary, these microtubules appear to be disjointed and the nematodesma is bent rather than straight. In the posterior girdle, the nematodesmata are short and stop at the proximal limit of the tela corticalis. In both the anterior and posterior girdles, the transverse microtubules of both kinetosomes in all pairs extend anteriorly under the cell membrane. Unlike those associated with the somatic and brush kinetosomes, the transverse microtubules on these kinetosomes do not continue from the proximal end of the kinetosome through the tela corticalis. In the anterior girdle, the microtubules from the nonciliated kinetosome of the pair line the membrane over the proboscis. Numerous accessory microtubules (= bulge microtubules (Foissner & Foissner 1988) arise perpendicular to these transverse microtubules. The accessory microtubules curve posteriorly and, as they descend through the proboscis, coalesce into nematodesmata-like groups that form the inner supporting structure of the oral apparatus. The transverse microtubules from the kinetosomal pairs in the posterior girdle extend forward under the cell membrane for only a short distance. No accessory, bulge microtubules were found originating perpendicular to them. (ref. ID; 4407)
(The brush (= brosse)) Posterior to both girdles are several short rows of cilia that make up the brush. They consist of paired kinetosomes lying one behind the other within the row. Both kinetosomes have short clavate cilia (ca. 2-3 um long) with an irregular ciliary membrane filled with granular material and a disorganized axoneme that lacks one or both central microtubules and sometimes one of the outer microtubular doublets. A nematodesma-like bundle of five to 11 microtubules projects straight into the cytoplasm from the proximal end of both kinetosomes. The posterior kinetosome of the pair has the same infraciliature as the somatic kinetosome: it has a kinetodesmal fiber, overlapping postciliary microtubules and two transverse ribbons with one microtubule descending from the proximal end of the kinetosome into the cytoplasm within a cylinder of electron-dense material. Throughout most of the length of the brush kinety, the anterior kinetosome of the pair possesses only the nematodesma but, at the ends of the brush kineties, it also gains the fibers of the somatic infraciliature. (ref. ID; 4407)
(Nonciliated kinetosomes) As described before in Didinium (Wessenberg & Antipa, 1968) and in Monodinium (Rodrigues de Santa Rosa & Didier, 1975), nonciliated isolated kinetosomes were often encountered under the plasma membrane between the ciliary girdles. These kinetosomes lie in rows that seem to be continuations of the somatic kineties but the individuals kinetosomes are oriented in all planes. They have a postciliary and two transverse microtubules but the kinetodesmal fiber is absent or short on many of them. The postciliary microtubules from these kinetosomes curve posteriorly and underlie the cell membranes in overlapping stacks. (ref. ID; 4407)
Measurements; Length 80-170 um. (ref. ID; 1219)
80-200 um long; spherical cysts with three walls, 60-80 um in diameter. (ref. ID; 1618)