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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Disematostoma

Disematostoma Lauterborn, 1894 (ref. ID; 2014)

Class Oligohymenophora: Subclass Hymenostomata: Order Hymenostomatida (ref. ID; 2014)

[ref. ID; 2014]
Outline-shape pyriform broad anteriorly, tapering back to a more or less bluntly pointed posterior end. Ventral surface flattened, dorsal surface convex. Oral aperture located approximately one third down the body in the shape of a right-angled triangle. The shortest side of the triangular aperture is posterior and the right angle is located on the animal's posterior right side. An undulating membrane on the right of the aperture with several rows of closely-set somatic cilia adjacent to it. Membranelles M1 and M2 follow the left edge of the aperture set closely to each other, while M1 is hook-shaped within the peristomial area. A definite post-oral suture follows the line of the undulating membrane backwards while a wide pre-oral suture travels from the anterior end of the oral aperture curving left. Somatic ciliation dense with the kineties curving with the contours of the body. There is a dorsal ridge in the posterior body half. Contractile vacuole centrally located, macronucleus sausage-shaped with one micronucleus.
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)
  1. Disematostoma butschlii Lauterborn, 1894 (ref. ID; 1622, 1629, 4237) reported year? (ref. ID; 1618) reported author and year? (ref. ID; 191), buetschlii Lauterborn, 1894 (ref. ID; 4488, 4611, 4613) reported author and year? (ref. ID; 5830)
    Syn; Leucophrys ovum Faure-Fremiet, 1924 (ref. ID; 4613)
  2. Disematostoma colpidioides von Gelei (ref. ID; 1618) reported author and year? (ref. ID; 191)
  3. Disematostoma frontoniiforme Gelei, 1954 (ref. ID; 5830)
  4. Disematostoma gyrans (ref. ID; 5830)
  5. Disematostoma invallatum Gelei, 1954 (ref. ID; 5830) reported author and year? (ref. ID; 1622, 4613)
  6. Disematostoma minor Michiels & Wilbert, 1973 (ref. ID; 5830) reported author and year? (ref. ID; 1622, 4613)
  7. Disematostoma tetraedrica (ref. ID; 5830)
  8. Disematostoma tentraedrica (Faure-Fremiet, 1924) (ref. ID; 1622) reported author and year? (ref. ID; 191)
  9. Disematostoma tentraedricum (Faure-Fremiet, 1924) Kahl, 1931 (ref. ID; 4611, 4613) reported author and year? (ref. ID; 1629)
    Syn; Leucophrys tetraedrica Faure-Fremiet, 1924 (ref. ID; 4611, 4613)

Disematostoma butschlii Lauterborn, 1894 (ref. ID; 1622, 1629, 4237) reported year? (ref. ID; 1618) reported author and year? (ref. ID; 191), buetschlii Lauterborn, 1894 (ref. ID; 4488, 4611, 4613) reported author and year? (ref. ID; 5830)

Synonym

Leucophrys ovum Faure-Fremiet, 1924 (ref. ID; 4613)

Descriptions

With or without zoochlorellae; in fresh water. (ref. ID; 1618)
Zoochlorellae-bearing ciliates. (ref. ID; 4237)

[ref. ID; 5830]
Disematostoma buetschlii is a freshwater ciliate which moves very fast in a rotatory fashion. In vivo it has a lanceolate shape with a rounded anterior and tapered posterior. However, fixed specimens adopt an ellipsoidal shape. The body is very variable in size and ranges between 198 and 106 um in length and 164 and 90 um in width. The nuclear apparatus consists of a long macronucleus, which is generally curved and rounded at both ends, and three or four spherical micronuclei. The somatic infraciliature is made up of 64-75 kineties arranged asymmetrically, of which five or six rows are postoral. The anterior ends of all these kineties delimit a wide preoral suture. This structure extends from the anterior extreme of the oral region to the apical end in a leftward curve. The postoral suture does not reach the posterior end of the body. It is the result of the more or less oblique confrontation between some right ventral somatic kineties and some left ventral kineties, including the postoral somatic kineties. In the middle zone of this structure, a thick argentophilic line can be observed, which is interrupted at the level of the cytoproct and later continues to the end of the suture. The convergence of the posterior ends of all the dorsal somatic kineties gives rise to the dorsal polar band (Kahl 1926) in the posterior half of the ciliate body. This band curves sharply to the left. In the middle part of the dorsal polar band, a row of 15-18 pairs of kinetosomes can be seen. The most posterior kinetosome in each pair has a long, thick derivate, fairly rigid in appearance, which is directed towards the posterior end. The entire structure of the dorsal polar band was called the "comb" by Kahl (1926) and interpreted as a set of thigmotactic cilia. Each somatic kinety is made up of oblique dikinetids. There is a parasomal sac to the right of dikinetids. The more posterior kinetosome bears a thick kinetodesmal fibre which dose not reach the anterior adjacent dikinetid of the same kinety. There is only a single contractile vacuole pore which is found on the dorsal side, to the left and near the anterior extreme of the dorsal polar band. The argyrome is a network of small rectangular polygons. Each somatic dikinetid is situated in the middle of a rectangle. A very small ring or triangular ramification can be observed at the right anterior vertex, which could correspond to the location of a trichocyst. Another argentophilic fibrillar system can be observed at a deeper level and is likewise composed of rectangular units. However, none of the rectangles coincides with the polygons of the above argyrome. In this fibrillar system, the dikinetid appears to be located at the left anterior apex of each rectangle. These is a connection between the dikinetid and the microfibrillar element that composes the left side of each rectangle of the deep network. Finally, it must be pointed out that in the segments of the right ventral kineties near the oral region, the dikinetids of different somatic kineties are aligned and limited anteriorly as well as posteriorly by thick argentophilic lines. These structures might be fibrillar in nature and they converge towards the ophryokineties (vestibular kineties). The oral region is found in the anterior ventral third of the ciliate body. There are four or five vestibular kineties or ophryokineties to the right of the oral cavity, three of which are longer than the others. The oral infraciliature consists of a paroral membrane and three peniculi located on the left in the buccal cavity. Peniculus 1 (P1) is long and has three rows of kinetosomes, the leftmost of which is the shortest because it does not reach the posterior extreme of this oral structure. Peniculus 2 (P2) is placed immediately to the right of P1 and has four rows of kinetosomes. It is more or less as long as P1 but begins more posteriorly. Peniculus 3 (P3), situated to the right at a fair distance from the other two oral peniculi, has four rows of kinetosomes. In addition to the infraciliary structures, D. buetschlii shows a complex buccal armature apparently made up of diverse structures which can be observed in impregnated cells and under optical microscopy. In the first place, there is a thick argentophilic band to the right of P3, which has the same length as this peniculus. A longitudinal argentophilic structure can also be observed between P3 and P2 but it is thinner than the aforementioned one. On the righthand side of the oral region one can see two thick longitudinal argentophilic bands joined by series of transverse connections. There are also several longitudinal rows of thick granules, each of which seems to coincide with an ophryokinety or vestibular kinety. (ref. ID; 5830)
  • Morphogenesis: In this species, stomatogenesis is first observed to take place when the paroral membrane proliferates in a posteroanterior gradient, giving rise to a series of short, oblique rows. This kinetosomal proliferation continues, producing a lanceolate field of kinetosomes which is located to the right of the parental paroral membrane. At a later stage, the kinetosomes of the oral primordium are rearranged longitudinally to form three groups of two rows in a posteroanterior gradient from left to right. During formation, the three penicular primordia of the opisthe migrate posteriorly. To their right one can observed an extended kinetosomal field which will constitute the future paroral membrane of the opisthe. An internal proliferation or alineation process then begins within each penicular primordium in such a way that each obtains the characteristic number of rows of the corresponding adult peniculus. During this process the posterior movement of the three penicular primordia continues and a kinetosomal group is observed at their anterior extremes, which disappears at a later stage. Simultaneously, the lengthened kinetosomal field located to the right of the penicular primordia becomes rearranged and gives rise to the paroral membrane of the opisthe. The parental paroral membrane also begins to duplicate in a posteroanterior gradient and generates the definitive paroral membrane of the proter. Once all the new oral structures of the opisthe are completely formed, they move as a whole posteriorly and to the left until they are located on the same axis as the oral structures of the proter, though in a more posterior position. Meanwhile the paroral membrane of the proter continues its rearrangement. The first two peniculi of the opisthe subsequently curve to the right, especially their anterior extremes, as the cortex deepens to form the oral cavity of the opisthe. With regard to the somatic infraciliature, the arrangement of the new oral structures of the opisthe is very advanced by the time the first signs of proliferation in the somatic infraciliary system are observed. Firstly, there is a longitudinal proliferation of the somatic dikinetids located in the middle third of the body. This process starts at the equatorial zone and extends towards the extremes. At the same time as this proliferation is taking place, the parental somatic kineties lose their kinetodesmal fibres, and soon after, both the somatic fibrillar lattice and the argyrome are no longer visible. The ophryokineties behave in the same way as the somatic kineties but the process of their proliferation begins earlier. As a result of proliferation, the somatic kinetosomes are distributed in longitudinal groups, each with two to four closely placed kinetosomes. Later, equatorial fission of all somatic kineties takes place and an annular nonciliated band appears between the pairs of cells and becomes more extensive as cellular elongation progresses. Simultaneously, there is a redistribution of the somatic kinetosomes in each kinety in such a way that the somatic infraciliature becomes uniform in the two cells. It is then possible to observe a kinetodesmal fibre in each pair of kinetosomes. The proter retains the parental preoral suture and the opisthe the dorsal polar band. The dikinetids, which will constitute the "comb" of the dorsal polar band of the proter, appear at the end of the leftmost ventral kineties of the proter. Each dikinetid has on its right a thick fibrillar derivate which is directed forwards, that is to say, with the same disposition as a kinetodesmal fibre. Later, the fission furrow is formed in the middle part of the annular nonciliated band between the proter and the opisthe. When the fission furrow constricts, the ventral part of the proter body moves forwards and then backwards. During these morphogenetic movements, the dikinetids of the comb migrate to the right until they reach the ventral surface of the proter. With regard to the nuclear apparatus, the micronuclei undergo mitosis. The macronucleus condenses and lies parallel to the anteroposterior axis of the ciliate body; it then lengthens gradually and later breaks into two elongated chromatinic masses. During macronuclear fission, a chromatin extrusion occurs. (ref. ID; 5830)

    Notes

    The shape, size, oral and somatic infraciliatures, and number of contractile vacuole pores of D. buetschlii differ clearly from those observed in Disematostoma invallatum (Gelei 1954; Didier 1971) and Disematostoma frontoniiforme (Gelei 1954; Dingfelder 1962). In our opinion, the inclusion of the last species in the genus Disematostoma is questionable because, on the left ventral side, the somatic infraciliature shows the symmetrical arrangement typical of the genus Frontonia. Furthermore, in studies by Gelei (1954) and Dingfelder (1962), the disposition of the dorsal somatic infraciliature is not described or illustrated and therefore the existence of the dorsal polar band, a diagnostic characteristic of the genus Disematostoma, is not proven. Disematostoma minor (Michiels and Wilbert 1973) is smaller, with a sharp anterior end and a penicular infraciliature different from that of D. buetschlii. In her description of Disematostoma tetraedrica, Roque (1961) pointed out the peculiar shape of this species, whose bilobulate posterior end is unlike that of the other species of this genus. The oral infraciliature is similar to that of D. minor but the number of ophryokineties is greater. Comparing our observations on the general morphology of D. buetschlii with observations of D. gyrans (Dragesco 1970, 1972; Dragesco and Dragesco-Kerneis 1986), we agree with Small and Lynn (1985) that D. gyrans is synonymous with D. buetschlii. In our opinion, the slight morphological differences shown by the "D. gyrans" described by the Dragesco are not very significant from the taxonomic point of view and would probably correspond to intraspecific variations among populations from different geographical regions. Our observations on D. buetschlii differ in some respects from the result obtained by Dragesco (1970) and Dragesco and Dragesco-Kerneis (1986). Firstly, in this species, as in other members of the family Frontoniidae, the number of micronuclei varies; there are usually three, though in some specimens four can be observed. All are small and spherical; they are placed very close to the macronucleus, and frequently even hidden by it. In contrast, Dragesco and Dragesco-Kerneis (1986) observed only one spherical micronucleus. In the remaining species this feature has not been described. However, we agree with Dragesco that the macronucleus of D. buetschlii varies greatly in size and shape during the cellular cycle. It should be noted that the dorsal polar band is not the prolongation of the postoral suture as stated by certain authors (Gelei 1954; Roque 1961; Michiels and Wilbert 1973), and furthermore, the argentophilic line that runs through the middle zone of this structure, called the comb by Kahl (1926, 1930-1935), in fact corresponds to a row of dikinetids. A long, thick derivate from the more posterior kinetosome of each pair extends backwards to the more posterior pole and was interpreted by Kahl (1926, 1930-1935) to be a thigmotactic cilium. Considering its morphogenetic origin, we thick that this derivate might be fibrillar in nature, but only ultrastructural studies will provide an answer. According to Dragesco and Dragesco-Kerneis (1986), the "apical" kineties on the dorsal surface converge in the middle part of the body to constitute a curved meridian suture which corresponds to Kahl's comb (1930-1935). As can be clearly observed in our photomicrographs, the posterior extremes of all the dorsal somatic kineties delimit the dorsal polar band in the latter half of the body. This structure, which Dragesco and Dragesco-Kerneis (1986) termed the dorsal meridian suture, curves sharply to the left in D. buetschlii. Gelei (1937) and Parducz (1962) observed tow networks in Paramecium by light microscopy, using silver staining. Later studies using electron microscopy have confirmed the organization of two networks in Paramecium (Pitelka 1965, 1969; Jurand and Selman 1969; Allen 1971; Ehret and MacArdle 1974; Garreau de Loubresse et al. 1988), Frontonia (Didier 1971; Gil 1981), and Disematostoma (Didier 1971). According to all these observations, there is an outer network (outer lattice) and an inner network (infraciliary lattice). In Disematostoma buetschlii the outer lattice (argyrome) is a network of rectangular units which gives a hexagonal appearance to some zones of the body, similar to descriptions of other peniculid ciliates such as Paramecium and Frontonia. Ultrastructural studies on D. invallatum (Didier 1971) reveal that this structure corresponds to ectoplasmic prominences and the remification of the right anterior vertex of each rectangle marks the location of an ectoplasmic trichocyst. The infraciliary lattice in D. buetschlii consists of compact microfibrillar bundles which form regular polygons around the proximal ends of basal bodies, as found in Frontonia (Gil 1981), with small rectangular units. However, in Paramecium (Allen 1971; Garreau de Loubresse et al. 1988) the infraciliary lattice forms an irregular polygonal mesh. In Frontonia leucas, Gil (1981) observed a connection between the kinetodesmal fibres and the infraciliary lattice. On the other hand, in D. buetschlii there seems to be a fibrillar connection between one of the somatic kinetosomes of each pair and the infraciliary lattice. The paroral membrane of D. buetschlii has two zigzag rows of kinetosomes and therefore corresponds to a stichodyad (Puytorac and Grain 1976). However, the paroral membrane appears as a very short single row of kinetosomes in the illustration by Dragesco and Dragesco-Kerneis (1986). According to our observations, D. buetschlii has four or five ophryokineties located to the right of the oral cavity, whereas the Dragesco described only three vestibular kineties, shorter than the oral peniculi, located in the oral cavity to the right of the paroral membrane. Dragesco (1970) pointed out that he had been unable to observe the vestibular kineties clearly because the "anterior" somatic kineties end almost perpendicularly on the right-hand edge of the buccal aperture. In his opinion, the first three kineties (from the apical end) consist of big, coalescent kinetosomes. Later, Dragesco and Dragesco-Kerneis (1986) recognized the existence of three ophryokineties, although they stated that this ciliate has prebuccal kineties with an almost annular disposition. We think that Dragesco (1970) and Dragesco-Kerneis (1986) made two erroneous interpretations; in the first place, the somatic kineties cross the ciliate body not transversely but longitudinally. In the second place, each somatic kinety consists of kinetosome pairs and all the kinetosomes are similar in size. According to our observations, the kinetal segments of the right ventral kineties located at the level of the oral zone have dikinetids delimited anteriorly and posteriorly by thick argentophilic lines which converge towards the ophryokineties. In the case of the kinetal segments on the left ventral kineties, we have observed that the dikinetids are delimited only anteriorly by a thick argentophilic line. For this reason, the system constituted by all the kinetosomal pairs placed at the same level but belonging to different somatic kineties, together with the argentophilic lines, appears as annular or transverse "kineties" (see Dragesco 1970; Dragesco and Dragesco-Kerneis 1986). In our opinion, the thick longitudinal argnetophilic band in the oral cavity and those to the right of the ribbed wall of this cavity could correspond to the nematodesmata and associated microfibrillar systems that form the characteristic buccal armature of certain peniculids such as Paramecium (Didier 1971) and Frontonia (Didier 1971; Gil 1981, 1984). In contrast, other members of this order, such as Urocentrum, have a buccal armature that is only microfibrillar in nature (Guinea et al. 1987) (ref. ID; 5830)
    [Morphogenesis]: The process of stomatogenesis during division has been studied only in D. tetraedrica by Roque (1961, 1973). According to this author, the formation of the new oral structures of the opisthe begins with the proliferation of the parental paroral membrane, except for its first 15-20 kinetosomes. As a result of this proliferation a new kinety is formed to the right of the parental paroral membrane. This new kinety then emigrates to a more posterior part of the body as it simultaneously proliferates to form a fusiform ciliary field between the first vestibular kinety and the parental paroral membrane. In D. buetschlii, as in D. tetraedrica (Didier 1971), the paroral membrane consists of dyads of kinetosomes and not a single row of kinetosomes, as stated by Roque (1961) when referring to the latter species. We have observed that stomatogenesis begins when the paroral membrane proliferates laterally towards the right, following a posteroanterior gradient, and gives rise to short oblique rows and later to an elongated kinetosomal field. The kinetosomes of this oral field are then rearranged into several longitudinal rows, which later on group into twos to form the three penicular primordia. In our opinion, Roque (1961, 1973) has mistakenly interpreted as a new kinety what is really the leftmost row of the P1 primordium. Once formed, this row lies rather separate from the parental paroral membrane. Furthermore, we do not agree with this author's interpretation that the parental paroral membrane does not undergo any modification before its "duplication". As can be observed in our photomicrographs, once the oral primordium of the opisthe is formed, the parental paroral membrane duplicates in a postero-anterior gradient and its kinetosomes are rearranged to constitute the paroral membrane of the proter. With regard to the changes in the somatic infraciliature, the longitudinal proliferation of the somatic kineties begins once the kinetosomal rearrangement process in the oral primordium has begun. Disematostoma buetschlii exhibits a similar division pattern to that described in Paramecium caudatum by Fernandez-Galiano (1978). In both species the kinetodesmal fibres disappear completely, and in the later stages of division, when the uniform distribution of the kinetosomes to each kinety has begun, new kinetodesmal fibres are formed, acquiring their characteristic length shortly before the proter and opisthe separate. Lastly, Roque (1961) explained the appearance in D. tetraedrica of a transverse furrow at the level of the ventral kineties located on the left of the oral region, which becomes evident as a result of the progressive curvature of these kineties. In our illustrations this furrow does not appear at this stage of division, and its existence does not seem possible because in Fig. 6 of Roque (1961), the progressive constriction of this transverse furrow involves the breakdown of the oral structures of the opisthe. In contrast, our observations show that only when the oral infraciliature of the opisthe is completely formed and has emigrated to a posterior ventral location do these oral structures acquire the longitudinal axis defined by the oral region of the proter. Then perikinetal fission of all the somatic kineties occurs, the cell elongates, and a nonciliated band appears between the proter and the opisthe. It is possible at this point to observe the fission furrow, which constricts to separate the cells. (ref. ID; 5830)

    Measurements

    135-155 um long. (ref. ID; 1618)

    Disematostoma colpidioides von Gelei (ref. ID; 1618) reported author and year? (ref. ID; 191)

    Descriptions

    Reniform, twisted. (ref. ID; 1618)

    Measurments

    100-160 um long. (ref. ID; 1618)