Pseudocohnilembus Evans & Thompson, 1964 (ref. ID; 2014, 4520)
Class Oligohymenophora: Subclass Hymenostomata: Order Scuticociliatida (ref. ID; 2014)
Class Oligohymenophora Puytorac et al., 1974: Order Scuticociliatida Small, 1967: Family Pseudocohnilembidae Evans & Thompson, 1964 (ref. ID; 4520)
Subclass Scuticociliatia (ref. ID; 7213)

[ref. ID; 2014]
Small (25-45 um long), slender oval to pyriform ciliate, somewhat flattened on the ventral surface. The peristome extends from near the apical pole to half to two-thirds the body length. Buccal ciliation consists of two large, relatively straight, parallel membranes lying along the right peristomial margin as in Cohnilembus. These membranes arise from two closely-set rows of kinetosomes which may be shown by silver impregnation using the protargol method. There are several argentophilic fibres in the peristome which are used for the identification of the species. Somatic ciliation in longitudinal meridians which do not reach either pole so that there is an unciliated apical cap and only a single caudal cilium at the terminal pole. The cytoproct is just posterior to the cytostome. Single terminal contractile vacuole. Spherical macronucleus centrally located with adjacent micronucleus. The genus is largely marine but Thompson observed some freshwater species in the Antarctic.
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; 3937]
Pseudocohnilembus are small organisms with a buccal cavity having two long membranes on the right side. Only during morphogenesis is the tetrahymenal organization of the buccal ciliature discernible. The genus currently contains four clearly distinguishable species: P. pusillus (Quennerstedt, 1869) nov. comb., P. putrinus (Kahl, 1928) nov. comb., P. hargisi Evans & Thompson, 1964, and P. marinus Thompson, 1966. The type species is P. pusillus, as designated by Evans & Thompson under the name P. persalinus. Borror (1972) proposed withdrawing Evans & Thompson's name Pseudocohnilembus in favor of Kahl's (1931) earlier Paralembus. This suggestion was evidently based on a misinterpretation of Kahl's (1931) report, which expressly pointed out that second membrane, present in Lembus (= Pseudocohnilembus), is lacking in Paralembus. Moreover, the buccal infraciliature of the two genera is very different; and Paralembus has strongly developed adoral membranelles that are lacking in Pseudocohnilembus. (ref. ID; 3937)

[ref. ID; 4520]
In 1964, Evans and Thompson established the genus Pseudocohnilembus with three new species P. persalinus, P. hargisi and P. longisetus. This genus is characterized by a buccal cavity containing two large membranes whose infraciliature consist of 2 parallel rows of kinetosomes nearly equal in length. So far, over ten species have been assigned to this genus. (ref. ID; 4520)


Pseudocohnilembus cantabricus Fernandez-Leborans & Zaldumbide, 1984 (ref. ID; 4679 original paper)
Diagnosis; Marine ciliata. Oval-shaped body with a pointed anterior end and a round posterior end. Size from 34.8-40.8 x 22.8-25.8 um. Round macronucleus in the anterior half of the body of 13.2 to 20.4 x 12-17.4 um. The micronucleus is adjacent to the macronucleus, disc-shaped of 3-3.48 um in diameter. 10 somatic kineties. Oral area is from 21-25.2 x 3.6-4.2 um in size. There are no membranelles in the oral area and there is only one paroral formation of 22.8-28.3 um in length composed of one anterior stichodyad and one posterior haplokinety. (ref. ID; 4679)
Description; Specimens of this species have a more or less oval shape with a pointed front and a round rear end. The macronucleus, more or less round, is located in the anterior half of the organism, just above the equator of the ciliate; it is from 13.2-20.4 um in length and from 12-17.4 um in width. The micronucleus is located beside the macronucleus; it is disc-shaped and is from 3-3.48 um in diameter. The surface of the organism is covered with somatic kineties which reach the anterior and posterior poles of the ciliate. The kineties end in a circular area, not only at the anterior pole but also at the posterior. In the center of the circular area of the posterior pole there is a thick kinetosome of the caudal cilia of the organism. In general there are 10 somatic kineties, with 20 kinetosomes each, although in some specimens 12 somatic kineties were found; in this case, two of these kineties, the ones adjacent to the oral area, do not reach the circular area of the posterior pole of the ciliate. The kinetosomes are quite clear and each has a thick and lengthy kinetodesmal fiber, arranged according to the law of desmodexy, which measures from 1.5-2.1 um. The oral area is located on the left side of the ventral surface of the ciliate from a zone near the anterior pole to beyond the equator of the ciliate, representing, more or less, 2/3 of the length or the organism; this oral region is from 21-25.2 um in length and from 3.6-4.2 um in width. In the adult stage no scutica has been observed.
[Oral Ciliature]: There is only one principal structure; the paroral formation (PF); the adoral zone of membranelles which is found in other scuticociliatida, is lacking. The paroral formation (PF) is located around the right side, the posterior zone and part of the zone before the oral area. It is from 22.8-28.2 um in length and has a thick fibre which is located below the components of the infraciliature of this structure. We have denominated this fiber, subparoral fiber (SPF). The anterior end of the PF is 3-3.6 um distant from the anterior pole of the ciliate and the posterior end of the PF is 24-25 um distant from the same pole. With respect to the infraciliature, the PF is divided into two parts: a) anterior, extending from the front end of the PF until, more or less 3/4 of its length. It is made up of pairs of kinetosomes, arranged in row (stichodyad) and is from 19.2-24.6 um in length; there are from 39-40 pairs of kinetosomes; each pair of kinetosomes has a straight fiber, which extends inwards toward the oral region; we have called this fiber, which is 1.5 um in length on the average, suboral fibre (SOF). b) posterior, located more or less, the posterior zone of the oral area, where the cytostome is located. It is from 3-6.6 um in length and is composed of kinetosomes that are arranged in zig-zag, forming a haplokinety. There are 24 kinetosomes that lack the suboral fibers that the kinetosomes have at the anterior. At the opposite end to that which connects with the anterior part, there are two curved fibers, more or less parallel and clear than the suboral fibers, which tend to complete the brace around the posterior zone of the oral area. These fibers, which we call perioral fibers (POF), measure 3.12 um in length. (ref. ID; 4679)
Comments; Taking into account the species of Pseudocohnilembus described by Evans and Thompson (1964) and most similar species of Cohnilembus, Pseudocohnilembus cantabricus is similar, with respect to size, to Pseudocohnilembus persalinus, P. hargisi, and Cohnilembus pusillus; however, it is different from these species with regard to the length of the buccal cavity (more than a third of the length of the body in P. catabricus; half of the length of the body in these species). The macronucleus is located in the front half of the body in P. cantabricus and in C. pusillus; the macronucleus is central in P. hargisi and P. persalinus. The number of somatic kineties only coincides with that of C. pusillus. The number of kinetosomes per kinety coincides with P. persalinus, but in this species there are only 8 to 9 somatic kineties. The size of the macronucleus is larger in P. cantabricus than in C. pusillus, P. hargisi, P. persalinus and P. longisetus. The species most similar to P. cantabricus is P. marinus. Both species have a similar size and the same number of somatic kineties; however, they vary in the number of kinetosomes of each somatic kinety (32 in P. marinus, 20 in Pseudocohnilembus cantabricus) (Wilbert and Kahan 1981). Other characteristics make P. cantabricus different from the species of the same genus: the structure of the oral infraciliature and that of its associated fibers and the arrangement of the somatic kinetodesmal fibers which have not been described for other species. (ref. ID; 4679)
Measurements; The body is from 34.8-40.8 um in length and from 22.8-25.8 um in width. (ref. ID; 4679)
Pseudocohnilembus hargisi Evans & Thompson, 1964 (ref. ID; 4520) reported author and year? (ref. ID; 7213)
Syn; Paralembus hargisi (Evans & Thompson, 1964) Borror, 1972 (ref. ID; 4520)
Description; In vivo about (38-46) x (14-18) um; with slightly variable body shape (depending on nutrition state). Body bluntly pointed anteriorly, rounded posteriorly. Ventral side usually more convex than dorsal side, anterior part somewhat bent dorsally. Cross-section circular with exception of depression of buccal cavity. Area of buccal cavity wide and somewhat flattened, extending from near anterior pole of cell about 1/2 (even 3/5 for some individuals) of cell length. Two membranes transparent and difficult to see in vivo. Pellicle smooth and flexible. Cytostome inconspicuous; distinctly visible cylinder-shaped cytopharynx located at terminus of membranes on right margin of buccal cavity; and directed (somewhat spirally in space) inward into cytoplasm. Cytoplasm colorless, containing many tiny (about 1 um across) and highly refractile granules densely distributed in the anterior half of body. Food vacuoles large (3-4 um), generally positioned in posterior half of body. Contractile vacuole large (4-5 um), caudally located, pulsating every 2-3 minutes. One large macronucleus (8-10 um) centered or somewhat anteriorly positioned, spherical in shape, with single micronucleus close to it. Cilia densely arranged, 4-5 um in length; single caudal cilium about 11-12 um long. Movement moderately fast, no special pattern except for rotating around longitudinal axis of body, usually motionless when feeding. Buccal apparatus consisting of 3 highly specialized membranelles (M1-3): M1 single-rowed and parallel to M2, positioned immediately anterior to paroral membrane (PM); M2 also composed of one row of kinetids, consisting of 40 basal bodies; M3 relative small, consisting of ca. 3 rows of kinetids (each with about 3 basal bodies) and positioned at posterior end of M2; PM consisting of two zigzagging rows of kinetosomes. All of the 13 rows somatic kineties arranged longitudinally, somewhat spirally (especially on the dorsal surface). Most kineties are dikineties, only those at the posterior end are composed of single basal bodies (usually 2-3 in number). Scutia (Sc) Y-shaped, consisting of about three paired basal bodies. Two (usually, seldom one) contractile vacuole pores (CVP) located at end of SK4 and SK5. The silverline system is directly connected with 3 circular intermeridional silverlines at the anterior part of the cell. Silverlines mainly along somatic kineties. Line along SK13 (first kinety to left of buccal field) crossing through polar circle gap and continuing to caudal cilium complex, extending dorsally and joining with the end of SK7. Cytopyge (CyP) as thick are argentophilic patch, subcaudally located posterior to cytostome. (ref. ID; 4520)
Analysis of the internal transcribed spacer 2 (ITS2) region. (ref. ID; 7213)
Comments; Morphologically, P. hargisi is similar to P. persalinus, P. marinus and P. longisetus in terms of habitat and body size; but even be distinguished, however, by the following combination of traits: 1) different number of somatic kineties (13-15 vs. 8-11), 2) conspicuously elongated cylindrical body shape (vs. generally oval to ellipsoid); 3) body size, 4) position of CVP and 5) the number of kinetosomes in somatic kineties. (ref. ID; 4520)
Pseudocohnilembus marinus Thompson, 1966 (ref. ID; 645, 3937)
Description; Shape oval to ellipsoid. Length ca. 37 um, width 22 um. 10 kineties from a slight rightward spiral, each with ca. 32 kinetosomes, paired anteriorly and single in the posterior third. One caudal cilium, half as long as the body. Contractile vacuole terminal, on the right. Cytoplasm clear. No resting posture. The silverline system exhibits a closed anterior circular fibril and an open posterior circular fibril. As in the genera Parauronema and Uronema, the last kinety of P. marinus passes through the gap in the posterior circular fibril and links the basal-body complex to the circular fibril. The excretory pore lies at the end of the 3rd meridian. J. C. Thompson (1966) gives its position as at the 4th meridian, and Borror (1972) between the 1st and 2nd. (ref. ID; 645)
A characteristics of the species is the small, horizontally oriented group of argyrophilic granules (basal bodies?) at the posterior end of the abbreviated inner membrane, which appears L-shaped as a result. According to Thompson, P. marinus has 10 ciliary meridians that run in a slight spiral. The contractile vacuole pore is near the posterior end of kinety 4; the silverline that passes dorsally from the caudal cilium joins the posterior silverline ring between kineties 5 and 6. By contrast, our population has only 8-9 kineties, and the contractile vacuole pore is near the posterior end of the kinety 3. The silverline running dorsally from the caudal cilium joins the posterior silverline ring between kineties 4 and 5. Such differences between the two populations are evidently brought about by the larger number of ciliary meridians in the population first described. Additional deviant characteristics are the size of the macronucleus, which is about twice as large in our strain, and the size of the body. The shape of our animals is a broad oval: that of Thompson's, a slender oval. The caudal cilium is ca. 18 um long. The silverline pattern in the region of the apical pole, not shown by Thompson, is typical of the genus. In the region of the buccal field the silverline system departs from the pattern drawn by Thompson in a few small details. There is a silverline running close to the left side of the outer membrane of the oral apparatus that is connected by short silverlines with ciliary meridian 1 and the anterior silverline ring. And the second (posterior) horizontally oriented silverline of the buccal field is nearer to the anterior end of the animal. (ref. ID; 3937)
Pseudocohnilembus persalinus Evans & Thompson, 1964 (ref. ID; 3937, 4520) reported author and year? (ref. ID; 191, 3753, 4006, 7213)
Description; Analysis of the internal transcribed spacer 2 (ITS2) region. (ref. ID; 7213)
Pseudocohnilembus pusillus (Quennerstedt, 1869) (ref. ID; 3937) or (Quennerstedt, 1869) Foissner & Wilbert, 1981 (ref. ID; 4611) reported author and year? (ref. ID; 1629, 7472)
Syn; Lembus pusillus Quennerstedt, 1869 (ref. ID; 4611)
Description; The infraciliature and especially the pattern of the silverline system departed only very slightly from those of P. persalinus as described by Evans & Thompson; it is highly likely that the latter species is but a local modification of P. pusillus. (ref. ID; 3937)
Trophic cells of P. pusillus isolated from Laguna Figueroa mat material range from 24.6-32.3 um in length with an average length of 27.7 +/- 2.0 um (n = 20), and range in width from 7.7-12.3 um with an average of 9.95 +/- 1.2 um (n = 20). Logarithmically growing ciliates had a wide, pyriform shape. As food was depleted in a culture, cells became smaller and more elongated with the anterior end bending to the right. Pseudocohnilembus pusillus possesses a single spherical macronucleus and a single anterior micronucleus in the center to anterior portion of the cell. This isolate has eight somatic kineties, composed of dikinetids and monociliated dikinetids with monokinetids at the posterior end of the cell. A double row of oral kineties (oral membranelle) measuring approximately 10 um is present on the right side of the buccal cavity. Pseudocohnilembus pusillus usually encyst in clumps near particles of food or organic debris. Most cysts were spherical measuring 15.5 +/- 1.7 um (n = 20) in diameter, but occasionally, ellipsoidal or pyrenoidal cysts were seen. Mature cysts have a conspicuous wall composed of a slightly refractile layer as viewed with Nomarski DIC optics. The slowly pulsating explusion vesicle, visible inside young cysts, disappears as cysts mature or desiccate. Although newly formed cysts tended to have attached bacteria, the cyst wall appears smooth and unornamented. At the onset of encystment, cells shorten, gradually becoming wider and more spherical. The anterior region becomes more dense and tends to point downward as they continue to swim. This de facto gravitropism restricts the view of encystig ciliates to a longitudinal perspective from the posterior end. Somatic cilia become immotile and splay laterally as encystment proceeds, whereas oral cilia continue to beat vigorously and propel the cell. The oral cilia cease beating 1-2 min after the somatic cilia. The somatic cilia wrap around the cell body; the ciliate becomes oblate to spherical with a smooth margin, as the cyst wall begins to form. The cytoplasm fills the entire wall volume in newly formed cysts. The cytoplasm in some older culture pulls away from the wall to assume an ellipsoid shape within the spherical cyst wall. In some four- to six-month-old cultures, especially those at lower salinities and food concentrations, cysts contained small granules motile by Brownian movement, shrunken ellipsoidal cells or shriveled cytoplasmic remnants. Oral and somatic kineties and macronuclei, but not micronuclei, are seen in newly formed cysts. Older cysts stain poorly; they lack definite kinetids and show evidence of macronuclei only. Well-fixed cyst from an 11-day-old culture examined with transmission electron microscopy showed a single, granular, cyst wall layer. Grandular material is also present in the intracystic space or lumen. Macronuclear and micronuclear structure, including condensed chromatn similar to that found in vegetative cells, is maintained in cysts. Mitochondria are visible at the periphery of the cell. Other cysts have large bodies that the seem to have cristae or striations, and are interpreted to be mitochondria. Numerous electron-dense bodies are also present. The kinetosomes and axonemes of both oral and somatic cilia are clearly visible within these cysts. (ref. ID; 7472)
Comments; Pseudocohnilembus pusillus differs from P. putrinus in the meridional course of the ciliary meridians, the position of the contractile vacuole pore, and the absence of scattered basal bodies in the region of the buccal field. On the other hand, it exhibits no significant differences from P. persalinus Evans & Thompson, 1964; The slight differences in size, body shape and infraciliature are not, in our opinion, sufficient to establish the two as separate species. The size and body shape of P. pusillus are strongly variable. In comparing our drawings with those of Evans & Thompson it should be noted that our animals were prepared by a dry slivering method in which the shape of the body is not as well preserved as in the wet method used by Evans & Thompson. In particular, the anterior taper expanded considerably during dehydration. The body shape of the Chatton-Lwoff stained specimens of P. pusillus population II was very similar to that described and figured by Evans & Thompson for P. persalinus. When the salinity of the medium in which P. persalinus is cultured is reduced, individuals with 11-12 ciliary meridians appear - a number that agrees well with our count in P. pusillus. Further points of agreement are the position of the contractile vacuole pore and the arrangement of the silverlines in the buccal field. Note, however, that in the rather highly diagrammatic drawing of Evans & Thompson (1964), the representation of the silverline pattern in the buccal field is only approximately correct if one takes the published photograph as a reference. The inner membrane of the oral apparatus of P. persalinus is somewhat shorter that the outer membrane, a feature that we did not observe in our dry-silvered specimen. This detail is discernible only in protargol preparations. In P. persalinus the silverline originating at the caudal cilium encounters ciliary meridian 4; in P. pusillus it joins the posterior silverline ring between the ciliary meridians 6 and 7. This difference is presumably due to the difference in the total number of meridians. Evans & Thompson (1964), unfortunately, made no explicit comparison of species-distinguishing characteristics of P. persalinus and P. pusillus. On the basis of our findings, and in view of the current state of knowledge of the genus Pseudocohnilembus, P. persalinus must be regarded as identical with P. pusillus, with names thus synonymous. The slight differences listed above do not justify separation of the two. If one were to take these differences as diagnostic features at the species level, then the forms of P. marinus Thompson, 1966 and P. hargisi Evans & Thompson, 1964, redescribed by Borror, as well as our P. marinus, would have to be ranked as new species, because these also differ somewhat from the original descriptions. In these cases, however, it is evident that they are only local variants. We also believe that the form described by Evans & Thompson (1964) and redescribed by Thompson as P. longisetus is only a local variant of P. pusillus. Cyclidium sapropellicum Vuxanovici, 1962 is also very likely identical with P. pusillus. This view is supported by the size, the body shape, and the triangular membranes of the mouth of this species, which are very similar to those known in P. pusillus. On the basis of our findings and the list of synonyms given by Kahl (1931), with which we agree, the following names of species must be regarded as junior synonyms of P. pusillus (Quennerstedt, 1869): Uronema marina Mobius, 1888, Lembadion ovale Gourret & Roeser, 1886, Lembus moebii Kahl, 1926, Cyclidium sapropellicum Vuxanovici, 1962, Pseudocohnilembus persalinus Evans & Thompson, 1964, and Pseudocohnilembus longisetus Evans & Thompson, 1964. (ref. ID; 3937)
Pseudocohnilembus putrinus (Kahl, 1928) (ref. ID; 3937) reported author and year? (ref. ID; 4611)
Description; The living organisms have the form of a slender oval in ventral view and measure 25-35 x 10-16 um. The tapered anterior end bears a conical frontal plate without cilia, set off somewhat from the remainder of the body. The posterior end of the body is usually rounded, though in some cases it is rather more pointed. Viewed from the side, the ventral surface appears distinctly flattened in the region of the oral apparatus. The anterior one-fifth is vent somewhat dorsally, so that the dorsal outline has a slight sigmoid curvature. The macronucleus is spherical to slightly ellipsoid and lies at the level of the buccal entrance. The nucleoli are small, spherical, and regularly distributed. Closely apposed to the macronucleus is a spherical to slightly ellipsoidal micronucleus. The pellicle is smooth and very elastic; it is only slightly indented by the ciliary meridians. The cilia in the anterior three-quarters of the kineties are 5-6 um long and are arranged in pairs. The cilia of the buccal membranes are about 4-5 um long in the anterior region. A caudal cilium, about 17 um in length, emerges from the center of the posterior pole of the body; the last third of it is bent, with its diameter reduced to a very fine projection. The endoplasm is colorless, and in the anterior half of the body there are many tiny, highly refractile granules. The food vacuoles are 2-5 um in diameter; usually they contain few bacteria, and in some cases they appear empty. Movement is very rapid and follows a broad spiral course. Sometimes the animal makes jumping movements, during which the cilia are splayed out. The ciliary meridians are spirally arranged, especially on the dorsal surface. The posterior polar field, which lacks cilia, is about 5 um in diameter. Kinety 1 crosses the buccal membranes at the level of the buccal entrance; this is discernible only in protargol preparation and in vivo. The slightly depressed buccal field is bounded on the right by two membranes of equal length, both are bent to the left at the posterior end and have basal bodies that appear to be arranged in a zig-zag pattern. The membranes begin ca. 3 um away from the anterior end of the body. The posterior one-fifth of the membranes extends into the narrow pharynx. At the posterior end of the buccal field there are always a few pairs of basal bodies in contacts with the silverlines of the buccal field and with that of the cytopyge. The silverline system has two components: the directly connecting silverline system, very similar in form to that of P. persalinus, and the indirectly connecting silverline system, which is discernible only after dry silver impregnation and has not previously been described. Its nature is unknown. As in many Scuticociliatida, it consists of approximately orthogonal meshes whose longitudinal strands run closely by the directly connecting silverlines of the ciliary meridians. It is absent from the nonciliated polar fields and from the buccal cavity. (ref. ID; 3937)
Comments; Pseudocohnilembus putrinus was described very superficially by Kahl, 1928. According to him, characteristics of this species, which he found in a plant infusion with fresh water, include a pointed posterior end of the body and a distinctly spiral arrangement of the ciliary meridians. Our identification was based on the spiral arrangement of the kineties and the biotope. The posterior end of the body was rarely as sharply pointed as Kahl drew it. The ciliary meridians of P. hargisi Evans & Thompson, 1964 are also spirally arranged. Moreover, this species resembles. P. putrinus in that the posterior, cilia-free polar field is notably large in comparison with the size of the body and the silverlines in the posterior part of the buccal field are not as curved as in P. pusillus. But it is very probable that these two species are not identical, for P. hargisi has 14 ciliary meridians and 1-3 (usually 2) contractile vacuole pores. (ref. ID; 3937)