Opercularia Goldfuss, 1820 (ref. ID; 2014) or Stein, 1854 (ref. ID; 1555) reported year? (ref. ID; 1248, 1618)
Class Oligohymenophora: Subclass Peritricha: Order Peritrichida: Suborder Sessilina (ref. ID; 2014)
Family Epistylidae Kahl, 1935 (ref. ID; 1248)

[ref. ID; 2014]
Colonial. Inverted bell-shaped zooids mounted upon branced non-contractile stalk. The peristome without a lip and its rim is often scalloped and rarely smooth. The macronucleus usually elongate, never rounded. But curved or C-shaped and held in a horizontal position. Often epizooic. The genus is easily mistaken for Orbopercularia which differs only by having a rounded macronucleus. It could also be confused with Epistlyis which has a definite peristomial lip.
Quote; Colin R. Curds, Michael A. Gates and David McL. Roberts "British and other freshwater ciliated protozoa Part II Ciliophora: Oligohymenophora and Polyhymenophora" Cambridge University Press, 1983 (ref. ID; 2014)

[ref. ID; 1555]
Type species; Opercularia articulata (Ehrenberg) Stein, 1854 (ref. ID; 1555)

Opercularia allensi Stokes, 1887 (ref. ID; 1557, 1620, 2245, 4610), allensii Stokes (ref. ID; 2861)
See; Opercularia nutans (ref. ID; 4610)
Description; O. allensii has zooids 60-140 um (in the average 100 um) and colonies up to 0.5 mm in diameter. In contracted state the individuals are hanging like at the precedent species. The stalks are longitudinally striated and irregularly segmented. The distal branches are relatively short. Catching bacteria, small algae and diatoms of the genus Navicula this species is common in spring and autumn in running and standing waters. It attaches to aquatic vegetation and easily also to the glass slides. (ref. ID; 2861)
Opercularia coarctata (Claparede & Lachmann, 1858) (ref. ID; 1219, 1620, 1629, 2245, 3664, 7614) reported year? (ref. ID; 2861, 4735, 4759), (Claparede & Lachmann, 1858) Roux, 1901 (ref. ID; 4610) reported author and year? (ref. ID; 191, 1555, 3689), cf. coarctata (ref. ID; 1557)
Syn; Epistylis coarctata Claparede & Lachmann, 1858 (ref. ID; 1113, 4610); Epistylis cylindrica Kusters, 1974 (ref. ID; 1113); Epistylis opercularia Stiller, 1942 (ref. ID; 1113); Opercularia arenicola Greeff, 1873 (ref. ID; 1113); Opercularia coarctata Roux, 1901 (ref. ID; 1113); Opercularia curvicaule Curds, 1964 (ref. ID; 1113); Opercularia fabrei Faure-Fremiet, 1905 (ref. ID; 1113); Opercularia frondicola Precht, 1936 (ref. ID; 1113); Opercularia gracilis Faure-Fremiet, 1904 (ref. ID; 1113, 1620); Opercularia halophila Kusters, 1974 (ref. ID; 1113); Opercularia microdiscum Faure-Fremiet, 1904 (ref. ID; 1113, 1620); Opercularia minima Kahl, 1935 (ref. ID; 1113, 1620); Opercularia reifi Matthes, 1950, 1951 (ref. ID; 1113); Opercularia sinuans Stiller, 1942 (ref. ID; 1113); Opercularia stammeri Matthes, 1950 (ref. ID; 1113); Rhabdostyla muscorum Kahl, 1935 (ref. ID; 1113); Telotrochidium johanninae Faure-Fremiet, 1950 (ref. ID; 1113)
Description; Colonies small, consisting of 3-6 individuals; body elongate; peristomal area small and not constricted form the body; buccal area with distinct oblique disk which is set off from the border by a deep incision; obvious undulating membrane. Macronucleus is horseshoe-like, its axis transverse to the longitudinal. (ref. ID; 1219)
O. coarctata has zooids 45-65 um long and stalks reaching 50-100 um. The colonies consist of only 3-6 individuals. The stalk is unstriated, slender, sessile on the flocks of activated sludge or among other slime organisms. Body is elongate, peristomial area small and not constricted from the body. There is a deep incision between the oblique disc and the peristomial border. The undulating membrane can be easily seen. Macronucleus is of the horseshoe-type, its axis is transverse to the longitudinal axis of the zooid. The pellicle is generally smooth and may be striated close to the stalk. The species is common in alpha-mesosaprobical environment, often together with Vorticella putrina and V. convallaria: oxidation ponds, biofilters, activated sludge, where it may reach an abundancy of more than 100,000 individuals per 1 ml. Nusch (1970) observed in experiments with sewage and brewery wastes a little different variety with 4-10 zooids in a colony. (ref. ID; 2861)
[Oral structures]: Light microscopy. The adoral ciliary spiral of Opercularia coarctata surrounds the epistomial disc and, after a half of turn inside the peristomial border, descends by the wall of the infundibulum. As in other Peritrichs, the adoral ciliature consists of a stichodyade (haplokinety) and a polykinety that run parallel in the peristomial region and separate within the infundibulum. A germinal kinety with disordered kinetosomes, about 20 um long, compains the stichodyade at the transitional region. Indeed, some specimens showed a few kinetosomes inside the adoral polykinety that form a very small epistomial infraciliature. Within the excentrically located infundibulum, the stichodyate describes 1 1/4 low pitch turns and the polykinety transformates in the adoral infundibular organelle 1 (P-1) as three rows become apreciable. These rows can branch at their end. The three rows of P-2 appear later at the right of P-1, and a short and somewhat disordered P-3 can be seen diverging from the end of the P-2. These P-3 appear to be located at a slightly raised level of the infundibulum. (ref. ID; 7614)
Electron microscopy. In the adoral ciliary spiral, the stichodyade occupies a raised position at the right side of the polykinety, kinetosomes of each pair beeing divergent distally. The barren kinetosomes have postciliary fibres with two or, rarely, three microtubules that go to the continuous fold over the row that is reinforced by interconnected electrondense nodules and fibrilles. There are two pairs of nodules over each kinetosome and others adhered to the lateral wall of the fold. The polykinety consists of transverse rows of ciliferous kinetosomes arranged in triads and connected by a complex fibrillary system. Postciliary microtubules were observed on the right kinetosomes. Opercularia presents three kinds of fibre signaled by Bradbury (1965), Z, Y, and the fibre towards the haplokinety, but lacks characteristically J fibres. The slender Y fibres connect at a middle level the triplet 7 of the left kinetosomes with the 5 of the right one. Broad and sptriated Z fibres link kinetosomes wit those inmediately in front and behind it. These fibres run from triplet 5 of posterior to the proximal end of triplet 1 of anterior kinetosomes and are better seen in somewhat obliquous sections. "Compound", V shaped, fibres run beneath posterior triplets of triads towards a reticulate ribbon below the stichodyade. Other bad characterized fibres connect the triplet 5 of a kinetosome with the 9 of the kinetosome on the left in the same triade, and triplet 3 of a kinetosome with triplets 5-6 of kinetosomes of the next left rows of the posterior triade. Aside of the "compound" fibres, a system of nodules and fibrilles, mainly linked to triplets 7 and 9 of kinetosomes of the right row, relates the polykinety to the reticulate ribbon. This reticulate ribbon consists of periodically arranged "compound" fibres (composite fibres of Eperon and Grain 1983) and simple fibres interconnected by fibrilles. In some images these fibres look as microtubules. In dividing specimens, the stichdyade was changing into the new polykinety. A ribbon of microtubules could be observed in the middle row of kinetosomes, and these have the same orientation that the postciliary microtubules of the future polykinety. (ref. ID; 7614)
Remarks; The oral infraciliature of Opercularia coarctata is very like to that of Opercularia arboricolum (Foissner 1981). Guhl (1979) has considered these species as probable synonims whereas Foissner (1981) thinks that are separate species. (ref. ID; 7614)
Examined material; O. coarctata was isolated from a pond water sample in Asturias (Spain). (ref. ID; 7614)
Measurements; Individuals 45-65 um, stalk about 50-100 um. (ref. ID; 1219)
Opercularia confusa Stiller, 1940 (ref. ID; 4610) reported year? (ref. ID; 2861)
See; Opercularia articulata Goldfuss, 1820 (ref. ID; 4610)
Description; O. confusa has zooids 85-90 um long and colonies consisting of 5-6 individuals. This species is living in the littoral zone of lakes, ponds and small water bodies on living as well as dead aquatic plants. The telotrochs leave the stalks without forming the aboral ring of cilia. The species can be classified as an indicator of natural decomposition processes common in all types of surface waters. (ref. ID; 2861)
Opercularia curvicaula (Penard) Curds (ref. ID; 2861)
Syn; Pyxidium curvicaula Penard (ref. ID; 2861)
Description; O. curvicaula resembles the species O. coarctata, but is smaller and slender. Zooids 40 up to 80 um, the stalk is inapparent, resembles a mycoidal hypha and supports a colony of up to 17 individuals. There are 3 whorls to the peristomial disc. The short macronucleus winds around the cytopharynx. The base of the body is finely striated but the rest of the pellicle is smooth. The food vacuoles are lemon-shaped. The species was originally described as Pyxidium curvicaule by Penard but redescribed by Curds (1964). In Great Britain Curds & Cockburn (1970) found it infrequently in biofilters and activated sludge. (ref. ID; 2861)
Opercularia microdiscum Faure-Fremiet (ref. ID; 2861)
Description; Zooids 70-90 um, abundant colonies up to 0.5 mm. The stalk is long, longitudinally striated, but not segments. The body is cylinder-like with a wide opening. The peristomial disc is borne upon a short process and is about one-fifth of the body width. The pellicle is striated and the macronucleus winds around the cytopharynx in the anterior region of the body. The single contractile vacuole opens into the wide pharynx. The number of food vacuoles and reserve granules is small. It was described as an epibiont on the larvae of Eristalis tenax living in highly polluted waters. Curds & Cockburn (1970) found it in biofilters, often is large numbers. (ref. ID; 2861)
Opercularia minima Kahl, 1935 (ref. ID; 1248) reported year? (ref. ID; 2861)
Description; O. minima has individuals 35-40 um on stalks which are much shorter than the zooids. Colonies consist of 2 or 4 individuals. The peristome disc is borne on a long process and the mouth region is quite wide. The pellicle is striated. There is one contractile vacuole. The macronucleus is situated in the upper half of the body and winds around the cytopharynx parallel to the peristome. The short stalk is longitudinally striated and segmented. The species was described as an ectocommensal on the legs of freshwater mites, but occurs also in moderate or small numbers in biofilters and activated sludge. (ref. ID; 2861)
Opercularia nutans (Ehrenberg, 1838) (ref. ID; 1219, 1248, 1620, 1629, 2245) reported year? (ref. ID; 2861, 3343) or (Ehrenberg, 1831) Stein, 1854 (ref. ID; 4610)
Syn; Epistylis nutans Ehrenberg, 1831 (ref. ID; 4610); Opercularia allensi Stokes, 1887 (ref. ID; 4610)
Description; Disk comparatively high and stalk more or less annulated (at least in the anterior region). (ref. ID; 1219)
O. nutans has zooids 60-140 um which are erect when whirling bur declined (hanging) when contracted. Abundant colonies reach up to 3 mm in size. The stalk is long, more or less annulated, mainly in the anterior region. The disc is comparative high. This species is attached to freshwater algae (Cladophora, Enteromorpha). To stones, insect larvae and easily attaches to submerged glass slides and can be classified as beta-mesosaprobic with inclination to alpha-mesosaprobity. It is one of the best and easily recognizable indicators of pollution of rivers and artificial reservoirs. (ref. ID; 2861)
Measurements; Individuals 60-141 um, colonies up to 3 mm. (ref. ID; 1219)
Length of cell 60 um. (ref. ID; 3343)
Opercularia phryganeae Kahl, 1935 (ref. ID; 4610) reported year? (ref. ID; 2861) reported author and year? (ref. ID; 1620)
See; Opercularia articulate Goldfuss, 1820 (ref. ID; 4610)
Description; O. phryganeae is 120 um long, colonies have 4-8 individuals, the stalk is striated longitudinally and segmented. The body is quite slender and elongated. The peristomial disc protrudes well out beyond the peristomial fringe. The fringe has a calloped edge. It was described originally as an epibiont on caddis-flies larvae but Curds & Cockburn (1970) reported it regularly in the community of biofilters, sometimes in large numbers. Finally it must be noted. That also other species of this rich genus may occur in saprobic milieu. We often meet 'Opercularia sp." in biological analytical results and one of the causes is that Liebmann (1962), listed in his excellent book only one species, O. coarctata, with a generalized figure. Much more identification work and good illustrations are still needed. (ref. ID; 2861)
Opercularia plicatilis Stokes, 1884 (ref. ID; 1620) reported year? (ref. ID; 1618)
Description; Pond water. (ref. ID; 1618)
Measurements; About 254 um long; colony 1.25-2.5 mm. high. (ref. ID; 1618)
Opercularia stenostoma Stein-D'Udekem (ref. ID; 1620) reported year? (ref. ID; 1618)
Description; Attached to Asellus aquaticus and others. (ref. ID; 1618)
Measurements; When extended, up to 125 um long. (ref. ID; 1618)