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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Pleurotricha

Pleurotricha Stein, 1859 (ref. ID; 2014)

Class Polyhymenophora: Subclass Spirotricha: Order Hypotrichida: Suborder Sporadotrichina: Family Oxytrichidae (ref. ID; 2014)
Family Oxytrichidae Ehrenberg, 1838: Subfamily Stylonychinae Berger & Foissner, 1997 (ref. ID; 4894 subfamily original paper)

Synonym Allotricha Sterki, 1878 (ref. ID; 2014, 4894); Onychodromopsis Stokes, 1887 (ref. ID; 2014)

[ref. ID; 2014]
Body flexible, elongate ellipsoid, sometimes tapered posteriorly. One row of marginal cirri on the left but two or three on the right joining posteriorly. Otherwise a typical front-ventral and transverse cirral system with the three most anterior frontal cirri being large. Caudal cirri absent. AZM large and extending a third to halfway down the body length. Macronucleus usually in two parts with adjacent micronuclei. A few species have been described.
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; 4894]
Improved characterization; Undulating membranes in Oxytricha pattern. Two or more right and one or more left rows of marginal cirri. Caudal cirri absent. No parental marginal cirri retained after division. Dorsal morphogenesis in Oxytricha pattern. (ref. ID; 4894)
Remarks; The inner right marginal row of the type species develops according to character state 22-1 (Borror & Wicklow 1982). In contrast, in Coniculostomum parental right marginal cirri are retained and form some inner right marginal rows (Kamra & Sapra 1990). Detailed morphogenetic studies are necessary to clarify the position of Pleurotricha within the cladogram. Possibly, it is closely related to Histriculus because of the lack of caudal cirri. Onychodromopsis and Parurosoma have a more slender and supple body and caudal cirri. (ref. ID; 4894)
Type species (original designation); Stylonychia lanceolata Ehrenberg, 1835 (ref. ID; 4894)

[ref. ID; 4920]
The genus Pleurotricha was originally described by Ehrenberg (1838) as Stylonychia lanceolata and has subsequently been reinvestigated by several authors (Stein 1859; Manwell 1928; Penn 1935; Kahl 1935; Jeffries and Mellott 1968; Dragesco 1970; Borror 1972; Hemberger 1982; Martin 1982; Fernandez-Leborans 1984; Martin-Gonzalez et al. 1984; Dragesco and Dragesco-Kerneis 1986; Foissner et al. 1991; Berger and Foissner 1997; Berger 1999; Song 2001). The taxonomic status of the genus has been reviewed and redefined (Berger and Foissner 1997; Berger 1999; Song 2001). Reported generic features of Pleurotricha include a rigid body, 18 Frontal-Ventral-Transverse (FVT) cirri, two undulating membranes (UMs) of the Oxytricha pattern, two or more rows of right marginal cirri (RMC), a single row of left marginal cirri (LMC), total resorption of parental marginal cirri during division and absence of caudal cirri (CC). Berger (2003) has recently observed small caudal cirri in the type species P. lanceolata. Morphogenesis of the dorsal structures is of the Oxytricha pattern. The cladistic relationship of the genus remains unresolved, as no detailed studies have been conducted. (ref. ID; 4920)
Redefinition; Inflexible oxytrichid (subfamily Stylonychinae, Berger 1999), 18-21 FVT cirri originating from, six primordia involving 5 parental cirri, transverse cirri in two groups in 3+2 pattern, one LMC, 2-3 RMC rows formed in the outer RMC row from a single primordium which splits later, total resorption of parental marginal cirri, three inconspicuous caudal cirri present. (ref. ID; 4920)
  1. Pleurotricha curdsi (ref. ID; 4920)
  2. Pleurotricha dubium (Gelei, 1954) Borror, 1972 (ref. ID; 4253)
  3. Pleurotricha grandis Stein 1859 (ref. ID; 4488, 4609) reported year? (ref. ID; 1335, 1629) or (Stein, 1859) Borror, 1972 (ref. ID; 4253)
  4. Pleurotrich indica Ammermann, Sapra & Schlegel, 1987 (ref. ID; 4253 original paper)
  5. Pleurotricha lanceolata (Ehrenberg) (ref. ID; 1618, 2129, 4111) or (Ehrenberg, 1838) Stein, 1859 (ref. ID; 4121, 4253) reported author and year? (ref. ID; 191, 4471)
    Syn; Stylonychia lanceolata Ehrenberg, 1838 (ref. ID; 4121)
  6. Pleurotricha mononucleata (Gelei, 1954) Borror, 1972 (ref. ID; 4253)
  7. Pleurotricha planensis Fernandez-Leborans, 1984 (ref. ID; 4253, 4695)
  8. Pleurotricha tihanyiensis (ref. ID; 191)
  9. Pleurotricha tschadensis Dragesco, 1972 (ref. ID; 4253)
  10. Pleurotricha variabilis Reuter, 1961 (ref. ID; 2129)

Pleurotricha curdsi (ref. ID; 4920)

Diagnosis

A fresh-water inflexible oxytrichid measuring about 140x65 um. Elongated oval in shape. Slightly pointed posterior end. Two ellipsoidal macronuclear nodes and two spherical a micronuclei. Adoral zone about 40% of body length. Twenty FVT cirri include 9 (rarely 10) frontals, 6 (rarely 7) ventrals and 5 (rarely 6) transverse cirri. Transverse cirri arranged in two groups of 3 and 2 separated by a gap. Two rows of RMC (rarely 3) and one row of LMC. Six dorsal bristle rows. Three inconspicuous caudal cirri placed on the right margin of cell. (ref. ID; 4920)

Descriptions

Cells of Pleurotricha curdsi are inflexible, dorsoventrally flattened and oval, tapering somewhat posteriorly. Protargol-impregnated cells measure on an average 140x64 um. The right margin of the cell is distinctly more convex as compared to the left margin. A single contractile vacuole is prequatorial lying in the left half at about the level of the cytostome. The nuclear apparatus consists of two ellipsoidal macronuclei and two spherical micronuclei. Cell movements are rapid and rotational. The generation time of the ciliate in the laboratory is 5+/-0.5 hr. Encystment is common and noticed within 24-36 hrs of starvation. The resting cyst is spherical and bears prominent species; the cysts wall appears similar to that of P. lanceolata (Penn 1935). On the ventral surface, the oral ciliature consists of a typical adoral zone of membranelles (AZM) shaped like a question mark along the left margin of the buccal cavity, extending to ~40% of the cell length and consisting of about 50 adoral membranelles (AMs). On the right wall of the peristome are two curved UMs of the Oxytricha type (Berger and Foissner 1997). The ventral ciliature includes 20 FVT cirri of which F(1-4) are hypertrophied. The F(1) is situated close to the UMs, F(2&3) are placed anteriormost at the same level, while F(4) is just below the first AM. F(5-8) are arranged in an oblique straight row adjoined by F(9). The two postoral ventral cirri (POVC) V(1&2) lie close to the posterior tip of the AZM; V(3-5) are a little posteriad while V(6) is located further posteriad after a long gap. Transverse cirri T(1-5) are arranged in two groups of three and two cirri. Each cell has a single LMC row and two RMC rows. The outer RMC row (RMC1) is longer than the inner row. RMC1 begins at the level of F(5), ending at the level of T(5). The LMC row begins at the anterior 1/3rd level of the cell and curves posteriorly along the left margin of the cell. Marginal cirri are equidistant in all the rows. The RMC rows and the LMC row are well separated posteriorly. The dorsal ciliature consists of four dorsal kineties (DK) and two dorsomarginal (DM) rows. While DK(1-4) traverse the entire cell length, DM(1&2) run about half and one fourth of the cell length respectively. There are three caudal cirri (CC) one each at the posterior ends of DK(1,2&4) placed in continuation with the terminal cirrus of the RMC1. The kinetosomal hypertrophy level of the CC matches that of the RMC, which makes them indistinguishable from each other in a vegetative cell. (ref. ID; 4920)
  • Morphogenesis: Stomatogenesis commences with the apokinetal appearance of basal bodies close to T(1). Further proliferation of kinetosomes results in the formation of an oral primordium (OP), which differentiates into the AZM of the opisthe. The proter inherits the parental AZM. The FVT primordia develop earlier for the opisthe. A few basal bodies separate from the anterior part of the OP to initiate the formation of the FVT primordia I-III. The ventral cirrus V(1) is associated with the formation of primordium IV and V(2) with the formation of primordia V and VI. F(8) disaggregates and contributes in the formation of primordia IV-VI for the proter. Later, F(1) and F(9) disaggregate almost simultaneously forming the proter's primordia II and III respectively. The parental outer UM disaggregates anteriorly to form primordium I. FVT primordia differentiate in a pattern 1,3,3,3,5,5. Two sets of primordia (one each for RMC1 and LMC) for the marginal rows develop in their respective parental rows. The primordia in RMC1 after elongation split into two. The marginal primordia thus formed differentiate into two RMC and one LMC rows for each of the daughter cells. Morphogenesis of the dorsal ciliature is also of the typical oxytrichid type. Two sets of three dorsal primordia DP(1-3) develop one above and the other below the prospective division furrow. The DP(3) splits transversely into two equal parts to provide the fourth dorsal primordium DP(4). The four dorsal primordia DP (1-4) differentiate into four dorsal kineties DK(1-4). DM (1&2) originate very close to the anterior end of the outer RMC primordium. Three CC form, one at the posterior ends of each of DP(1,2&4) and align themselves along the new RMC(1). (ref. ID; 4920)

    Remarks

    The morphostatic ciliature of P. curdsi resembles that of a fresh-water Chinese isolate reported as Allotricha curdsi (Shi et al. 2002). It appears that A. curdsi (Shi et al. 2002) is actually a Pleurotricha species, hence the new combination. A. curdsi sensu Shi et al. (2002) was reported to be flexible bodied; later this has been clarified as a misobservation and cells are stated to be rigid (Berger 2003; Song 2003). Additionally, the morphogenetic data of A. curdsi (Shi et al. 2002) is insufficient. The authors have given no data on the early origin of OP and FVT primordia and also do not mention the exact number of parental cirri involved in the formation of FVT primordia. Their claim that the morphogenetic pattern is similar to that in Allotricha antarctica, Berger 1999 (= Onychodromopsis flexilis, Petz and Foissner, 1996) makes the matter more confusing. O. flexislis is definitely a member of Oxytrichinae and uses 6 parental FVT cirri for FVT primordia formation. Under these circumstances it is very difficult to make a worthwhile morphogenetic comparison between the Chinese and Indian populations. All features of A. curdsi sensu Shi et al. (2002) are indicative of it being a member of subfamily Stylonychinae. We propose that the Chinese population be reassessed. The strong synapomorphy between the two is seen in the method by which multiple right marginal rows are generated in both populations. An African population of P. lanceolata described by Dragesco and Dragesco-Kerneis (1986) with 21 FVT cirri also appears to be a population of P. curdsi. However, this description is inadequate and reliable comparison with P. curdsi is not possible. (ref. ID; 4920)

    Pleurotricha dubium (Gelei, 1954) Borror, 1972 (ref. ID; 4253)

    Descriptions

    See description of P. indica. (ref. ID; 4253)

    Pleurotricha grandis Stein, 1859 (ref. ID; 4488, 4609) reported year? (ref. ID; 1335, 1629) or (Stein, 1859) Borror, 1972 (ref. ID; 4253)

    Descriptions

    See description of P. indica. (ref. ID; 4253)

    Pleurotrich indica Ammermann, Sapra & Schlegel, 1987 (ref. ID; 4253 original paper)

    Diagnosis

    Pleurotricha indica n. sp. has an average size of 220x119 um. The body is firm and inflexible. The ciliature consists of six rows of dorsal cilia, two rows of right marginal cirri (RMC), and one row of left marginal cirri (LMC). The pattern of the fronto-ventral-transverse cirri (FVT) is similar to that of genus Oxytricha. Normally, three prominent caudal cirri (CC) are present the parts of the macronucleus are variable in number and shape. (ref. ID; 4253)

    Descriptions

    The body is firm and inflexible. The average length of slightly starved cells is 220 um +/-15%. The dorsal ciliature consists of four rows of curved kineties (1-4) and two straight to slightly bent kineties (5 and 6). Usually three long caudal cirri differentiate at the tip of kineties 1, 2, and 4. Occasionally were observed one to two addition caudal cirri. In our preparation, a sample of 30 protargol-stained cells for one clone, we found two deviations from the above mentioned ventral ciliature. One cell showed an arrangement of three frontal and four ventral cirri a line which looked like a third row of RMC. Another cell showed three rows of LMC. In Pleurotricha lanceolata there is also a surprising variation mainly in the number of RMC and LMC within one clone. The macronucleus of Pleurotricha indica has a highly irregular and variable shape from cell to cell even within a clone. It consists of 2-6 connected macronuclear parts. Three to ten micronuclei (mean 6+/-28%, n=10) with a diameter of 3 um are present. (ref. ID; 4253)

    Comments

    The characteristic of P. indica are not new: however, their combination is not found in any related species. In the following, we compare P. indica with other species, which according to Borror (1972) and Hemberger (Ph.D. dissertation, University of Bonn, West Germany, 1982) belong to the genus Pleurotricha: In our opinion this comparison shows clearly that P. indica is a true species of the genus Pleurotricha, which can be readily identified by its morphological features. (ref. ID; 4253)

    Type locality

    Keoladeo Ghana Bird Sanctuary, Bharatpur (27 degrees 15'N, 77 degrees 30'E) Rajasthan, India. (ref. ID; 4253)

    Type material

    The holotype of P. indica (a slide with protargol-stained cells of one clone) is deposited in the Zoological Collection of the University of Tubingen, FRG. (ref. ID; 4253)

    Pleurotricha lanceolata (Ehrenberg) (ref. ID; 1618, 2129, 4111) or (Ehrenberg, 1838) Stein, 1859 (ref. ID; 4121, 4253) reported author and year? (ref. ID; 191, 4471)

    Synonym

    Stylonychia lanceolata Ehrenberg, 1838 (ref. ID; 4121)

    Descriptions

    2 macro- and 2 micro-nuclei. (ref. ID; 1618)

    [ref. ID; 4121]
    Pleurotricha lanceolata has a dorsoventrally flattened body and has a lengthened oval shape with a rounded fore end and a slightly sharp rear end. The nuclear apparatus has two ellipsoidal macronuclear nodes. Two spherical micronuclei lie very close to them. (ref. ID; 4121)
  • Oral Infraciliature: The adoral zone of membranelles (AZM) beings close to the right antero-lateral margin of the ciliate and then continues to the front end of the body, forming a curve which borders the peristome and finishes slightly to the left of the antero-posterior axis of the ciliate. This structure consists of 45-55 membranelles. The first membranelle is made up of three rows of kinetosomes, one short and two longer ones of equal length. The rest of the membranelles have four rows of kinetosomes: a very short kinety with three to four kinetosomes, two long kineties of equal length and an intermediate row of medium length. The last membranelle has only three rows of kinetosomes, one of these rows being very short with only three kinetosomes and the other ones of the same length. The right side of the peristome is bordered by two ciliary membranes: the outer undulating membrane (paroral membrane) and the inner undulating membrane (endoral membrane). Both membranes are about the same length although they begin at different levels, because only the endoral membrane reaches the posterior apex of the peristome. Each one has two closely packed rows of kinetosomes. (ref. ID; 4121)
  • Ventral Somatic Infraciliature:
  • Frontoventral cirri (FVC): Pleurotricha lanceolata always has 13 frontoventral cirri, larger than marginal cirri and of different shapes. Two topographic subgroups can be distinguished in this group of cirri; the frontal cirri, placed in the right anterior fore half of the ventral surface and the ventral cirri placed in the latter half of the body. The frontal cirri are eight in number. The buccal cirrus (F1) is most anterior and is found close to the anterior end of the paroral membrane, slightly to its right. This buccal cirrus has nine rows of kinetosomes. There are three other cirri to the right of the buccal cirrus (F1). The foremost one (F2) is placed immediately to the right of the buccal cirrus and has eight rows of kinetosomes; the next frontal cirrus (F3) is close to the first membranelle of the AZM with eight rows of kinetosomes and the third one is located immediately to the right of the paroral membrane and has ten rows of kinetosomes. The other frontal cirri are smaller, two of them having six rows of kinetosomes, another one (F5) with five rows of kinetosomes, and the last (F7), the one closest to the endoral membrane, with seven rows of kinetosomes. There are five ventral cirri (V1-V5), they have ten, seven, six, nine, and seven rows of kinetosomes, respectively. (ref. ID; 4121)
  • Transverse cirri (TC): There are five transverse cirri (T1-T5). These transverse cirri are fond on the latter third of the body ventral surface where they form the J-shaped arrangement typical of the hypotrichous ciliates included in Oxytrichidae. Each of the transverse cirri exhibits 9, 10, or 11 rows of kinetosomes. Neither the frontoventral nor the transverse cirri have kinetodesmal fibers nor does P. lanceolata have caudal cirri. (ref. ID; 4121)
  • Dorsal somatic Infraciliature: The dorsal somatic infraciliature consists of rows of dorsal bristle units which run longitudinally over the dorsal surface. Two of the rows are shorter and do not reach the posterior end of the body. Each dorsal bristle unit has two kinetosomes. The front one presents a short and thick transverse fiber (T) and bears a cilium. The unciliated posterior kinetosomes has a longer and thinner fiber that, due to its location, would correspond to a postciliary fiber (PC). (ref. ID; 4121)
  • Some Observations on the Fibrillar Systems: There is a thick perimembranellar fiber (PMF) which surrounds the adoral zone of membranelles on its external edge. Some fibrillar bundles emerge from this PMF and more or less form right angles with it. We have termed these bundles intermembranellar fibers (IMF) since they are situated between two adjacent membranelles of the AZM. Each of the membranelles of the AZM at the anterior margin of the organism gives rise to two types of fibrillar bundles which have the same appearance and location as the A and G bundles described in Stylonychia mytilus. We have also observed some fibrillar connections between several membranelles of the AZM and the three anterior cirri. (ref. ID; 4121) Resting cyst: Outer cyst wall folded into spine-like projections. (ref. ID; 4111)

    Comments

    Although our observations of P. lanceolat complete the description made by Jeffries & Mellott (1968), our observations differ significantly from some of the data reported by Dragesco (1970) for this species. Jeffries & Mellott (1968) confuse the first membranelles of the AZM with cirri. In the organisms observed we have found that the AZM has 45-55 membranelles each of them usually consisting of four rows of kinetosomes of different length as has been described in other hypotrichs in the Oxytrichidae; however, it must be pointed out that both the first and the last membranelle of the AZM have only three rows of kinetosomes. We think that this may be a common feature in other hypotrichs although it has not been described till now. Neither of the undulating membranes has a single row of kinetosomes but instead has two. The inner undulating membrane (endoral membrane) is always formed by a ciliated row of kinetosomes in those hypotrichs that have been examined, for example, Paraurostyla weissei, Pseudourostyla cristata, Keronopsis rubra, Gastrostyla seinii, Oxytricha fallax, Stylonychia mytilus. So P. lanceolata represents an exception to the uniform composition of the endoral membrane in hypotrichs. Furthermore, comparative study of the morphology and ultrastructure of the outer undulating membrane (paroral membrane) shows that there is a great variability in these ciliates. According to Bakowska & Jerka-Dziadosz (1978): "the number of ciliary rows in the outer membrane does not correspond with the average size of a given species but rather it is correlated with the extent of specialization (or evolutionary differentiation)". So the less evolved species, such as Paraurostyla weissei, G. steinii, K. rubra, and P. cristata have a polystichomonade pattern. But in the more evolved species such as O. fallax and S. mytilus, the outer membrane has only one row of kinetosomes. The paroral membrane composition of P. lanceolata might indicate an intermediate evolutionary stage. Nevertheless, morphogenetic studies still have to be made to establish its phylogenetic relations. We agree with Jeffries & Mellott (1968) in the number and distribution of the cirri which compose the frontoventro-transverse system (FVT system) in P. lanceolata; however, our description of the composition and the arrangement of the kinetosomes in each of these cirri disagrees with the observations of these authors. According to Jeffries & Mellott (1968), the three foremost ventral cirri are of equal size, which is similar to that of the transverse cirri and the rest of the ventral cirri. As may be observed in our photomicrographs, there are some great differences in the number of rows of kinetosomes among the ventral and transverse cirri and even among the frontal cirri. In the P. lanceolata described by Dragesco (1970), the FVT system is formed by nine frontal cirri, five to six ventral cirri and six transverse cirri disposed in a pattern which differs greatly from the figures given by Jeffries & Mellott (1968) and our own observations. In addition, Dragesco (1970) noted that the cilia of the last two left marginal cirri were longer than those of the other marginal cirri and he considered the possibility that these two cirri were, in fact, caudal cirri. On the other hand, the dorsal somatic infraciliature does not have seven rows of dorsal bristles (Dragesco 1970) but six longitudinal rows (Jeffries & Mellott 1968); however, in both studies the dorsal bristle unit is described as being composed of only one kinetosome. We think that the hypotrich described by Dragesco (1970) is not really the species P. lanceolata when one takes into account the great morphological differences between the observations of Dragesco and other descriptions of P. lanceolata in respect to the following characteristics: 1) the number of dorsal bristle rows, 2) the distribution and number of FVT system cirri, and 3) the possible existence of caudal cirri. (ref. ID; 4121)

    Measurements

    100-165 um long. (ref. ID; 1618)
    It is 200-250 um long and 100-120 um wide. (ref. ID; 4121)

    Pleurotricha mononucleata (Gelei, 1954) Borror, 1972 (ref. ID; 4253)

    Descriptions

    See description of P. indica. (ref. ID; 4253)

    Pleurotricha planensis Fernandez-Leborans, 1984 (ref. ID; 4253, 4695)

    Descriptions

    See description of P. indica. (ref. ID; 4253)

    [ref. ID; 4695]
    Paroral formation: The paroral formation (PF) is located more or less in the middle zone of the oral area, in anterioposterior direction, extending from the posterior region of the adoral zone of membranelles (AZM) to near the anterior part of this membranelle zone. The frontobuccal cirri field is situated to the right of this formation, which is composed of two structures:

    Pleurotricha tschadensis Dragesco, 1972 (ref. ID; 4253)

    Descriptions

    See description of P. indica. (ref. ID; 4253)