The World of Protozoa, Rotifera, Nematoda and Oligochaeta
Metacineta
Metacineta Butschli, 1889 (ref. ID; 2013)
From Dr. InakiFrom Dr. Inaki
Class Kinetofragminophora: Subclass Suctoria: Order Suctorida: Suborder Exogenina (ref. ID; 2013)
[ref. ID; 2013]
Body spherical to pyriform lying centrally within a distinct lorica which extends posteriorly to form a stalk-like region of variable length. The lorica is characteristically pierced by 5, 6 or 8 vertical slits through which the capitate tentacles protrude. The macronucleus is rounded and there are 1 or 2 contractile vacuoles.
One species Metacineta pentagonalis Nozawa, 1939, which has a very short stalk-like extension to the lorica could be easily confused with the genus Solenophrya if viewed from above.
Quote; Colin R. Curds "British and other freshwater ciliated protozoa Part I Ciliophora: Kinetofragminophora" Cambridge University Press, 1982 (ref. ID; 2013)
[ref. ID; 3475]
The genus Metacineta was created by Butschli (1889) for Cothurnia mystacina (Ehrenberg). (ref. ID; 3475)
This form, found on Ceratophyllum in fresh-water (probably, but not expressively said in North America), shows the general habitus of a long-footed Metacineta with the characteristic feature of a hollow footpart with its wall and cavity continuous with that of the widened anterior part of the lorica. The former was from six to eight times as long as the latter, the total length measuring around 1/56 inch (=453 um). The widened part of the case, which contains the plasmatic body, is described by Stokes as follows; "Lorica irregularly ovate, widest centrally, the length not greatly exceeding the breadth, tapering anteriorly to the rounded or obtusely pointed border, and posteriorly to the pedicle, the walls thin, transparent, continuous, traversed longitudinally by from five to eight posteriorly diverging, compressed, wing-like elevations, each pierced by about four ovate, equidistant, longitudinally arranged apertures for the passage of the fascicles." The enclosed zooid is said to be "ovoid, somewhat changeable in shape, occupying the anterior part of the cavity of the lorica, apparently not attached to the walls; endoplasm granular; tentacles fasciculate, all the distinctly capitate extremities usually placed on the same side of the fascicle, each of which consists of about six tentacles; nucleus ovate, subcentral; contractile vesicle single, spherical, posteriorly situated near one lateral border...The projecting wing-like additions are very strongly flattened, the margins usually being undulate or irregularly crenate...The usual number seems to be five; it varies, however." -Stokes drawing shows no distinct basal disc and a Ratio Rl of about 6. The occurrence of longitudinal folds of the wall, protruding outwards from the widened part of the lorica, is alone nothing extraordinary. To the J. Rieder experience it is fairly often seen, especially in thinwalled forms, during prolonged fasting periods, when the plasma occupies only a small fraction of the inner space of the lorica. What, however, is outstanding in the discussed animals as described by Stokes, is the feature that, instead of simple clefts extending basewards from the anterior border of the case and situated on the crests of the folds (as seen in other forms of Metacineta) there are rows of several separate oval opening through which the tentacles are extruded. This is a clearcut criterium, which distinguishes the form in question from all other types of Metacineta. Assuming that, although astonishing, it corresponded to reality in a considerable population and was not just an individual aberrance or reposed on an error of observation, J. Rieder thinks that the animal described can be regarded as a separate variety of Metacineta. It has not been signalized again after its discovery. The appropriate name for the organism discussed would be Metacineta longipes var. alata Stokes, 1885 (ref. ID; 2020)
Stokes's original description: Lorica obovate or subspherical. Lorica obovate, the length only slightly exceeding the width, flexible, continuos, taking the form of the enclosed zooid, the anterior border rounded, the lateral margins almost straight, tapering to the pedicle. Lorica subspherical, the anterior border slightly undulate, the anterior extremity of the pedicle suddenly expanded. Pedicle from seven to nine times as long as the lorica, hollow, its cavity continuos with that of the sheath; enclosed body usually entirely filling the lorica, soft, changeable in shape, not attached posteriorly to the sheath; endoplasm granular, enclosing numerous, large, refractive, probably amylaceous corpuscles; tentacles irregularly distributed at the anterior border, distinctly capitate, exhibiting spiral folds during their retraction; contractile vesicle apparently single, posteriorly placed near one lateral border; nucleus not observed. Length, including pedicle 1/100 to 1/70 inch (=254 to 363 um). Habitat: Pond-water; attached Myriophyllum".
The organisms concerned was ranged by Sand (1901) in the genus Tokophrya, by Collin (1912) in the genus Discophrya, but neither one of these authors has offered any argument for his opinion. In fact there exist no reasons, on which the classifications cited, including the one by Stokes, could be based. Matthes (1954) remarked, without other indications, that the form considered would be "offensichtlich eine schlecht beobachtete und verkannte Metacineta mystacina". He has thus recognized correctly the true genus, into which the suctorial must be classified. The uninterrupted continuity of the wall and the cavity of its lorica from the widened part to the footpart is indeed a typical feature of the taxonomic group Metacineta. The opinion, however, that the animals dealt with belonged to the species M. mystacina, appears inadequate today. A secure judgment on this problem did require further and more thorough observations of a multitude of individuals, which also revealed their variability-range. Such additional examinations became possible only in 1976 and 1981, when J. Rieder has refound the organism in question, for the first times since their discovery by Stokes, in two habitats of Switzerland. The results of analyses performed on the Swiss specimens. Rieder considers this form as the typus of a separate species, which he introduces under name Metacineta macrocaulis (Stokes 1887) nov. comb. The essential character, by which it differs from all other species of Metacineta, is not the long or large foot, as the name given by Stokes could insinuate (and which is shared by several other forms). It rather consists in the fact that the anterior end of the lorica does not possess typical longitudinal clefts of its lateral wall, through which the tentacles pass in corresponding number of separate fascicles, but that its apical border shows, in sparingly fed individuals, around a large permanently open apical aperture only sinuate retractions that may flatten out completely in richly nourished animals. Through the unique opening mentioned all tentacles are stretched out in one single, diverging tuft. Therefore a much more adequate species-designation would have been "monofasciculata". (ref. ID; 2020)
Maskell's original description: Lorica cup-shaped, width nearly equal to the length, anterior margin deeply cut and produced in several fine points, which bend over slightly inwards; pedicle very little more than half as long as the lorica, very slender. Animalcule sub-globular, a little dilated at the anterior edge, occupying only the upper portion of the lorica; bearing numerous fine tentacles which protrude between the points of the lorica. Length of lorica, exclusive of pedicle and points, 1/750 inch (=33.3 um). Allied to A. mystacina Ehrenberg, but very much smaller; also the lorica is wider and rounder in proportion. (ref. ID; 2020)
J. Rieder opinion: Maskell's clear drawing reveals in addition the following details: The footpart of the lorica is hollow and its wall and cavity are continuous with those of the widened part, which is a typical feature of Metacineta. The anterior border of the case does not show deep fissures, but rounded bays between the prominent points, and surrounded as a whole a unique apical opening about circular in shape, since the sidewalls are rounded without longitudinal folds. A basal disc is not visible. The tentacles are of the capitated type; they are not grouped into fascicles but are irregularly distributed over the entire apical face of the cell body and radiating from there like the water rays from the rose of a watering can. There is one contractile vacuole situated latero-posteriorly. Maskell says nothing about the nuceli and multiplication. If one assumes that in this respect the form in question corresponded to the general diagnosis of the genus Metacineta and that- although it has never been signalized after its discovery -its structure was biologically stable, the erection, not of an own species, but of a separate variety can be accepted. The latter must then be considered as a sub-entity of the same species as the former "Acineta macrocaulis Stokes" that was published in the same year 1887 and which is claimed in this paper to be the types of a newly introduced species Metacineta macrocaulis. It is characterized by a permanent large aperture, instead of multiple narrow clefts, at the anterior end of the lorica and (essentially) by the concentration of all tentacles in one single apical tuft. The classification mentioned leads in turn to the new name Metacineta macrocaulis var. flos Maskell, 1887. (The species-name does appear misleading in view of the tiny footpart of the lorica, but it responds to priority rules). (ref. ID; 2020)
[ref. ID; 2020]
It was found among aquatic plants in the Lake Biwa (Japan) in summer 1398 and then multiplied in a Petri dish, where it feeded preferently on Paramecium caudatum. (ref. ID; 2020)
Nozawa's description: The test is more or less pyriform, and attached to the substratum by a short, narrowed end, the real stalk being absent. (A later remark further mentions a thin disc at the base). It is thin and transparent in both young and old individuals. There are five slits running longitudinally on the test, which give it an appearance of a regular pentagon in the apical view. In some specimens the corners are obtuse, and the outline approaches a circle in apical view. The slits begin from the point one-third from the posterior end, and converge to the apical end. The sucking tentacles are distinctly capitated and spring through the slits; they are isolated and never united in the proximal parts, into a bundle like in M. mystacina. There are 30-100 tentacles springing from each slit, which reach about two times the diameter of the test when wholly extended. The protoplasmatic body is spherical or ellipsoidal, and central. The macronucleus is granular, ovoid and central. The contractile vacuole is single, excentric, and located on the posterior side of the nucleus. The division (probably by external budding) of a young suctorian has been observed in several cases. Neither tentacle nor cilia is distinct in such young individuals; only an ellipsoidal macronucleus and a contractile vacuole are visible. Dimension: Height of test 100 um (60-120 um), diameter of test 62 um (50-70 um). (ref. ID; 2020)
J. Rieder's opinion: The animals so described could be considered identical with Metacineta micraster (Penard) Batisse 1967, or its variety Metacineta micraster (Penard) Batisse 1967 var. pedanta, if there were not the following details of Nozawa's text that have discriminating importance: First: the presence of between 30 and 100 tentacles protruding through each cleft of the lorica; second: the extraordinary length of these clefts (equal to two thirds of the length of the lorica); third: the indication that Nozawa has examined about 100 individuals, which obviously all showed the same features. The first two of these statements reveal a difference to the typical Metacineta micraster as well as to its variety var. pedata, which both always show less than 20 tentacles per slit and a length of the clefts never notably surpassing one half of the length of the lorica. (Nozawa's remark that in each slit of her M. pentagonalis the tentacles are "isolated and never united in bundle like in M. mystacina" is not significant, because actually the repartition of the tentacles along one and the same cleft varies considerably in the two other forms mentioned). The fact that Nozawa has examined abut 100 specimens is on the other hand, although not a warrant, at least an indication for morphological constancy over several generations. In conclusion, the three arguments cited plead for the idea, that the suctorians recorded by Nozawa as Metacineta pentagonalis represent a separate systematic entity. But, here again their characteristic features seem adequate to justify only the erection of an own variety, not of a new species. Rieder propose to register them under the designation Metacineta micraster (Penard) Batisse 1967 var. pentagonalis Nozawa, 1939 nov. comb. (ref. ID; 2020)
Mature stage without any cilia but with suctorial tentacles that are arranged in 6 groups at the anterior end; no cytostome; food ingestion by means of the tentacles; the stalked lorica is attached to the substrate (stones, plants, artificial substrates, glass slides); 1 spherical macronucleus; a single contractile vacuole. Asexual reproduction by exogenous budding; the free-swimming ciliated bud undergoes metamorphosis to the sessile mature stage. (ref. ID; 1219)
Ehrenberg has published in 1831 (without giving a figure) the first notice on a member of the genus called today Metacineta, under the designation "Cothurnia? mystacina". In 1838 he ranged the species mystacina within a new genus Acineta and added the fist drawings, which allow to recognize undoubtably the suctorian in question. They show lateral views of three specimens with different lengths of the footpart of their loricas and one can clearly see that this foot is hollow with its cavity being a continuation of that of the widened part of the hull, which contains the protoplasm. The description of the organism, assembled form all papers of Ehrenberg, only say that the animal lives in fresh-water, has a crystal-clear, membranous case ("Panzer") with a diameter of "1/72 to 1/48 linie" (about 42-63 um) of globular to cup-like shape, fixed by a stalk to a substrate, and bears at its upper end fascicles of many long, thin, retractible but not whirling threads with capitated endings (the tentacles) which Ehrenberg interpreted as "Fuhlfaden". The number of their fascicles was erronously indicated with two. The ovoid to spherical plasmatic body would be of yellowish colour and contain and "ovarium" (probably corresponding to small food-vacuoles), many "Magenblasen" (corresponding to larger food-vacuoles) and a somewhat clearer, rounded body "similar to a seminal gland" (corresponding to the macronucleus). The micronucleus, the pulsating vacuole and the characteristical configuration of the apical end of the lorica were not detected and the processes of nutrition and reproduction were unknown to Ehrenberg. Concerning taxonomy Ehrenberg thought that the structure of the animal would give it a position between the pennate Diatoms and peritriche Ciliates. (ref. ID; 2020)
Measurements
Body about 35-100 um in diameter, tentacles up to 150 um, lorica up to 800 um. (ref. ID; 1219)
Lorica up to 700 um long. (ref. ID; 1618)
Length of cell 65-100; length of stalk 500-700 um. (ref. ID; 3343)
This form was found by Stokes in a non specified freshwater near Trenton N.J., attached to Spirogyra. (ref. ID; 2020)
Stokes original description: Acineta flexilis, sp. nov. - Lorica irregularly subspherical, tapering posteriorly to the short, hollow pedicle; anterior border closed, thin, apparently perpendicularly lamelliform, the margin irregularly undulate; two opposite lateral regions each bearing two anterior approximating, posteriorly diverging, narrow fissures for the passage of the tentacles, the fissures usually being open only sufficiently for the passage of the tentacles, except during the final development and the escape of the embryo, when those on the lateral margins and that on the frontal border are seen to be continuous, the expanding fissures closing after the escape of the embryo; pedicle about one-seventh as long as the lorica; tentacles capitate, of two kinds and apparently issuing only from the slit-like lateral fissures, one kind being straight, rigid, and not often exceeding twice the length of the lorica, the other form filamentous, flexible, writhing and variously curved and coiled, often extending to more than five times the length of the lorica; body of the animalcule subspherical or obpyriform, not filling the cavity of the lorica, and in no way adherent to it; endoplasm granular; nucleus broadly ovate, located near one lateral border; contractile vesicle single, spherical, postero-lateral in the region opposite the nucleus. Length of lorica, including the pedicle, 1/560 inch (=45.4 um).
The unique drawing reveals that the attached end of the lorica possessed a small, but well developed basal disc. Neither the drawing nor the description can furnish a secure idea of the apical and of the lorica. It remains even doubtful, whether the organism has a monaxone radiary symmetry or is bilateral symmetrical. Among the more clearly stated features there are two which appear strange. One is the presence of only four apico-lateral fissures of the lorica. Although this number of clefts is not outside the inhearent construction possibilities of Metacineta, it has otherwise be seen only in certain stalkless cysts of the forms, not in the test of their trophic stage, which is prolonged in a footpart. The other surprising character is the alleged possession of two types of tentacles, one straight and rigid, the other within and variously coiled. Personally J. Rieder is convinced that Stokes has seen these two aspects, but does not believe in their presumed different natures. Such a duplicity would be absolutely foreign to the construction-plan of Metacineta. One can rather imagine that all tentacles were of the same type and that the coiling of some of them was the expression of a reaction or affection caused by one or several extraordinary conditions. Stokes says nothing about the ability of these coiled tentacles to fix and suck out a prey nor does he mention how many of these specimens he has seen or if their characters were stable over successive generations. Later on they have never been signalized again. The total situation is such, that for the form in question the erection of an own species is certainly not acceptable and that the qualification for a near variety seems uncertain. J. Rieder proposes that up to obtainment of complementing information the animal is provisionally registered under the designation Metacienta mystacina forma inquirenda flexilis A.C. Stokes, 1894. (ref. ID; 2020)
Maskell's original description: "Lorica trapezoidal, the sides below tapering sharply and straight down to the pedicle; anterior edges angular, produced into two sharp points, which bend over leaving openings at the sides. Pedicle nearly as long as the lorica, tapering to a fine point at the base, wider above. Animalcule irregular, widest anteriorly, occupying only the upper part of the lorica and bearing two fascicles of capitate tentacles, which protrude through the side openings. Contractile vesicle posteriorly situated. Length of lorica, exclusive of pedicle and points, somewhat variable, from 1/350 inch (=71 um) to 1/300 inch (=83 um); width at the lower angles 1/430 inch (=58 um). Allied to A. mystacina Ehrenberg, but the straight sides and sharp angles are constant and distinctive. (ref. ID; 2020)
J. Rieder's opinion: Although not expressively indicated by Maskell, one can savely deduce from both, his text and his drawing, that fully metamorphosized "Acineta angularis" had a bilateral symmetry and only two clefts. Rieder assumes this to be a secondary acquired feature and thinks that the animal in question should be regarded as a separate variety of Metacineta mystacina. It would thus have to be registered under the name Metacineta mystacina var. angularis (Maskell, 1887). The report by its discoverer has as yet remained the only one on this form. (ref. ID; 2020)
[ref. ID; 2020]
It was found on the shells of Viviparus in a pond in Husimi (Rokuzizo), Kyoto in June 1937 by Mr. R. Yoshii. (ref. ID; 2020)
Nozawa's original description: The test is pyriform or balloon-shaped, with the stalk-like end extending slightly. It is transparent in young specimens, but incrusted with sand-grains and other foreign particles older specimens. The wall of the test is thickest in the stalk-like end. There are 8 longitudinal slits running on the test, and the test appears like a regular octagon in the apical view in young specimens. The sucking tentacles spring through these slits, without forming any bundle as in Metacineta mystacina (Ehrenberg). They are 15 to 30 in number, and shorter than the length of the test. The corners of the octagonal test become more obtuse in adult individuals. The body is pyriform and placed in the center of the test. The macronucleus is ovoid and central. Usually two contractile vacuoles are present, one on either side of the nucleus.
Dimensions: Length of the test up to 140 um, breadth of test 90 um.
Remarks: The present species resembles somewhat the young specimen of M. mystacina in its general appearance, but it may be distinguished from the latter by three points tabulated below: Moreover The length and the proportion of the foot to the widened part of the lorica that are indicated for M. mystacina correspond rather to the values of Metacineta longipes Mereschkowsky, 1879. The apical configuration of the slits is not mentioned in the article of 1938. But in Nozawa's paper of 1939 the author includes two schematic drawings, suggesting that, when the plasma dose not fill the lorica completely, the valves join at the apex, without leaving a common opening larger than the breadth of the slits. Nothing is said on the micronucleus, on reproduction and on the structure of the swarmer. The foot shows a slight basal widening. The ratio Rl is guessed from the drawings to be 1:4-5. (ref. ID; 2020)
J. Rieder's opinion: Rieder deems that, although no information is given on the number of individuals seen and on the constance of their characteristics over several generations, the animal in question must be accepted as a separate form of Metacineta, the nature and degrees of its distinguishing features are, however, such that they can justify only the erection of an own variety, but not of a species. Consequently the name would have to be Metacineta mystacina (Ehrenberg) var. yoshii Nozawa 1938 nov. comb. (ref. ID; 2020)
Metacineta micraster var. pentagonalis (ref. ID; 2020)
Descriptions
The test is more or less pyriform, and attached to the substratum by a short, narrowed end, the real stalk being absent. It is thin and transparent in both young and old individuals. There are five slits running longitudinally on the test, which give it an appearance of a regular pentagon in the apical view. In some specimens the corners are obtuse, and the outline approaches a circle in the apical view. The slits begin from the point one-third from the posterior end, and converge to the apical end. The sucking tentacles are distinctly capitated and spring through these slits; they are isolated and never united in the proximal parts, into a bundle like in M. mystacina. There are 30 to 100 tentacles springing from each slit, which reach about two times the diameter of the test when wholly extended. The protoplasmic body is spherical or ellipsoidal, and central. The macronucleus is granular, ovoid, and central. The contractile vacuole is single, eccentric, and located on the posterior side of the nucleus. Sometimes a young individual with an undeveloped test is seen attached to the anterior side of the test of the adult. The division (probably by external budding) of a young suctorian has been observed in several cases. Neither tentacle nor cilia is distinct in such young individuals; only an ellipsoidal macronucleus and a contractile vacuole are visible. (ref. ID; 3475)
Comments
This species was discovered in summer 1938 among the aquatic plants in Lake Biwa. It was brought to the laboratory and multiplied in a Petri dish, containing the lake water to which grains of rice were added. The suctorian preferred Paramecium caudatum to any other ciliate. The test is more or less pyriform, and the part with which it is attached to the substratum is very short, and ends in a thin disc at the base. The lateral view of the thin transparent test resembles that of a young specimens of M. mystacina (Collin, 1912-13, p.187, Fig.53). The distinctive feature of the new species consists in the five longitudinal slits on the test. The number can be determined only by an apical view. Kent (1882) says on M. mystacina that "lorica urceolate, subdivided at the anterior or distal margin into five or six acuminate, triangular, valve-like lobes..."; but he gives a figure only of a form with six slits. Many other investigators such as Stein (1854), Butschli (1889), Collin (1912-13) Schoenichen (1927) and Kahl (1934), also have described or figured M. mystacina with six slits, but none of them recorded a form with five slits. Thus the record of a metacinetan with five slits is found only in Kent, and it does not seem to have been observed in Europe. I examined about 100 individuals which appeared in the culture in a Petri dish, and found that all of them were provided with five slits without exception. Thus if Kent's description is correct, the metacinetan seems to be M. pentagonalis or its allied species and not M. mystacina. In M. mystacina the tentacles springing from each slit are united into 3 to 10 bundles. In the new species the tentacles are isolated, and are 30 to 100 in number for each slit. The protoplasmic body is spherical or ellipsoidal, and usually leaves a wide space between the test, which is filled up when the suctorian is well fed. The macronucleus is ellipsoidal, but shows no characteristic feature. The contractile vacuole is single, and placed eccentrically under the nucleus as in M. mystacina. The reproduction is probably by the external budding, though I have not yet observed a ciliated embryo. Kent gives a figure of M. mystacina with a young suctorian attached to the test of the adult. I have found a young with an incomplete test adhering to the outside of the test of a adult individual. As stated above, this new metacinetan resembles both of the known species, but it seems to be more nearly related to M. mystacina than to M. yoshii. (ref. ID; 3475)
Measurements
Height of test 100 (60-120 um), diameter of test 62 (50-70 um). (ref. ID; 3475)
The test is pyriform or balloon-shaped, with the stalk-like end extending slightly. It is transparent in young specimens, but incrusted with sand-grains and other foreign particles in old specimens. The wall of the test is thickest in the stalk-like end. There are 8 longitudinal slits running on the test, and the test appears like a regular octagon in the apical view in young specimens. The sucking tentacles spring through these slits, without forming any bundles as in Metacineta mystacina (Ehrenberg). They are 15 to 30 in number, and shorter than the length of the test. The corners of the octagonal test become more obtuse in adult individuals. The body is pyriform and placed in the center of the test. The macronucleus is ovoid and central. Usually two contractile vacuoles are present, one on either side of the nucleus. (ref. ID; 3475)
Comments
The present species resembles somewhat the young specimens of M. mystacina in its general appearance, but it may be distinguished from the latter species by the three points below; [M. mystacina] Length of test: up to 900 um. Stalk-shaped end: extraordinarily long, 5 times the length of main part of the test. Number of longitudinal slits: 6, so the contour of test is hexagonal in the apical view. Contractile vacuole: single. [M. yoshii] Length of test: 140 um only. Stalk-shaped end: very short, gives the test a pyriform appearance. Number of longitudinal slits: 8, so the contour of test is octagonal in the apical view. Contractile vacuole: two, one on each side of the nucleus. (ref. ID; 3475)
Type locality
On the shells of the Viviparus found in a pond in Husimi (Rokuzizo), Kyoto (June 1937) (coll. Mr. R. Yoshii). (ref. ID; 3475)
Measurements
Length of test up to 140, breadth of test 90 um. (ref. ID; 3475)
