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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Siroloxophyllum

Siroloxophyllum Foissner & Leipe, 1995 (ref. ID; 7355 original paper)

Ciliophora: Pleurostomatida (ref. ID; 7355)

[ref. ID; 7355]
Diagnosis; Loxophyllidae with oral bulge surrounding almost entire cell. Three perioral kineties extending from anterior end to mid-body. Single brush kinety near dorsal margin. Single right dorsolateral kinety. (ref. ID; 7355)
Remarks; Kahl (1931) transferred Amphileptus utriculariae (Penard 1922) to Loxophyllum. This was accepted by Song & Wilbert (1989), who reinvestigated the species using protargol impregnation. Our investigations show that A. utriculariae belongs neither to Amphileptus nor Litonotus (because it lacks a median suture and has a right dorsolateral kinety) nor to Loxophyllum, whose left anterior end is occupied by a conspicuous field of paired brush cilia (Foissner et al. 1995) which was overlooked by Song & Wilbert (1989). The most conspicuous character of Siroloxophyllum is the string-like patterned oral bulge surrounding almost the entire cell, leaving blank only a small area at the anterior dorsal end. This feature is not easily recognized in living and protargol impregnated cells. However, if one is aware of its existence, it can be seen well under interference contrast. Recent SEM observations showed that the oral bulge of very likely all pleurostomatid ciliates is patterned string-like (Foissner et al. 1995). The distinctiveness of the pattern varies; usually it is most conspicuous in suboptimally prepared specimens. Thus, the pattened oral bulge of Siroloxophyllum is not unique, but it is exceptional in surrounding almost the entire cell. It is non known whether S. utriculariae can open the whole bulge during feeding or -like other members of the family (Foissner et al. 1995)- only that portion which is accompanied by the paired basal bodies of perioral kineties 1 and 2. Likewise, the mechanism which unlocks the bulge between perioral kineties 1 and 2 is obscure. Possibly, the transverse microtubular ribbons of the oral kinetids are involved. An even more difficult character is the dorsolateral kineties. A left dorsolateral kinety is very likely present in all pleurostomatids (although often not designated or recognized as such), possibly with the exception of Loxophyllum meleagris, and located between the dorsal bruch kinety and the rightmost somatic ciliary row or the right dorsolateral kinety (Foissner and O'Donoghue 1990; Foissner et al. 1995). The left dorsolateral kinety, which was considered as regular left lateral somatic ciliary row by most previous authors, differs clearly from the left lateral kineties by being continuous with the monokinetidal tail of perioral kinety 1; from the rightmost somatic ciliary rows of the right side and from the right dorsolateral kinety it differs by the short, stump-like cilia. Right dorsolateral kineties are present only in Loxophyllm, which has two (Foissner et al, 1995), and in Siroloxophyllum, which possesses only one. The right dorsolateral kinety(ies) differs from the right lateral ciliary rows by surrounding the posterior end of the cell, forming a more or less distinct suture with the abutting ends of the regular somatic kineties. The structure and/or location of the dorsal brush of Siroloxophyllum differ distinctly from Loxophyllum, Pseudoamphileptus and Opisthodon, but are similar to Litonotus, Acineria and Amphileptus. Thus, none of the four characters given in the genus diagnosis is unique to Siroloxophyllum, i.e. it is only the specific combination of the characters which separates the new genus from its relatives. (ref. ID; 7355)
Systematic relationships of Siroloxophyllum and classification of pleurostomatid ciliates; Traditionally, all pleurostomatid genera are lumped in a single family, Amphileptidae Butschli (Butschli 1887-1889; Corliss 1979; Kahl 1931). However, Foissner & Foissner (1988) split the pleurostomes into two suborders, viz. Amhileptina and Litonotina and recognized two families, viz. Amphileptidae and Litonotidae. More recently, Lipscomb & Riordan (1990) suggested a very different classification based on cladistic methods, using, however, many unproven character states. They assigned to the pleurostomes not only lacrymariids and didiniids but also classical haptorids like Spathidium, Bryophyllum and Homalozoon. We believe that this was an unsuccessful upset, simply because the distinct asymmetry of the pleruostomatid oral and somatic ciliature is hardly found in any classical haptorid, with the notable exception of Homalozoon, a highly thigmotactic and specialized predator. Furthermore, Lipscomb & Riordan (1990) did not take into account the different types of stomatogenesis occurring in pleurostomes s.str. (monotelokinetal) and haptorids s.str. (holotelokinetal; see (Leipe et al. 1992) for definition of terms and literature). Obviously, their classification neglects two main features and is thus very likely artificial. (ref. ID; 7355)
Etymology; Composite from the Greek words siro (string), loxos (oblique) and phyllum (leaf). Neuter gender. Name refers to string-like appearance of oral bulge. (ref. ID; 7355)
Type species; Amphileptus utriculariae Penard, 1922. (ref. ID; 7355)
Type specimens; One holo(genus)type slide and one voucher slide of protargol impregnated Siroloxophyllum, Munich population, have been deposited in the collection of microscope slides of the Oberosterreichische Landesmuseum in Linz (LI), Austria. Accession numbers: 26, 27/1994. The slides also serve as neotypes for the species, Amphileptus utriculariae Penard, 1922, because Song & Wilbert (1989) made no mention of deposited neotype material. (ref. ID; 7355)
  1. Siroloxophyllum australe (Foissner & O'Donoghue, 1990) Foissner & Leipe, 1995 (ref. ID; 7355 redescribed paper)
    Syn; Loxophyllum australe Foissner & O'Donoghue, 1990 (ref. ID; 7355)
  2. Siroloxophyllum utriculariae (Penard, 1922) Foissner & Leipe, 1995 (ref. ID; 7355 redescribed paper)

Siroloxophyllum australe (Foissner & O'Donoghue, 1990) Foissner & Leipe, 1995 (ref. ID; 7355 redescribed paper)

Synonym

Loxophyllum australe Foissner & O'Donoghue, 1990 (ref. ID; 7355)

Remarks

A reinvestigation of the protargol impregnated type slides of Loxophyllum australe (Foissner & O'Donoghue, 1990) showed that it has the main characteristics of S. utriculariae. Thus, it has to be transferred to this genus: Siroloxophyllum australe (Foissner & O'Donoghue, 1990) nov. comb. The two species differ mainly in the number of macronuclear nodules, usually two in S. utriculariae and four in S. australe. The number of right end left lateral somatic kineties is slightly higher in S. utriculariae than in S. australe. Very likely, other species will be added, e.g. Loxophyllum carinatum Vuxanovici and L. semilunare Vuxanovici (both redescribed in (Song and Wilbert 1989), but seemingly without dorsolateral kinety and thus not definitely assignable). (ref. ID; 7355)

Siroloxophyllum utriculariae (Penard, 1922) Foissner & Leipe, 1995 (ref. ID; 7355 redescribed paper)

Descriptions

Size highly variable within and between populations, in vivo 65-270x20-80 um according to our observations and literature data (Kahl 1926, 1931; Penard 1922; Song and Wilbert 1989), usually about 140-200x30-60 um; up to 30% contractile, fixed and stained specimens thus smaller due to contraction and shrinkage. Shape likewise highly variable, often, however, lanceolate with widest portion in or close underneath mid-body, anterior half usually more distinctly narrowed than posterior and slightly curved dorsally, but not snout-like as in Loxophyllum; anterior end narrowly rounded, posterior end broadly rounded elongated. Field material flattened leaf-like (up to 4:1), with very flat and hyaline, about 7 um wide fringe containing extrusomes. Right side flat to slightly concave, left more or less distictly vaulted bearing 3-8 distinct crests in central third; crests 2-5 um high and 2 um wide, gradually flattened toward body ends, become inconspicuous and even disappear in well-fed specimens. Nuclear apparatus in or near centre of cell, stands out as bright blister against darker, granulated cytoplasm. Usually two macronuclear nodules and one micronucleus; number constant in Berlin and Bonn population, highly variable in specimens from Munich with, however, a median of two as in the other population. Macronuclear nodules small as compared to size of cell, slightly ellipsoid, often close together (< /_ 2 um), micronucleus then not within but on cleft; nucleoli roundish, distributed throughout nodules. Micronucleus slightly ellipsoid, 2-3x2 um, within or on cleft formed by macronucler nodules. Two contractile vacuoles, each with numerous excretory pores on right surface, in anterior and posterior third of cell, respectively; anterior vacuole near ventral side, posterior vacuole near dorsal side, thus forming highly characteristic diagonal pattern with nuclear apparatus in between. Extrusomes (toxicysts) 6-8 um long, thin (diameter about 0.4 um) and slightly curved, both ends evenly rounded; anchored in single line, and possibly in pairs, to oral bulge, some scattered in cytoplasm, never aggregated to warts as in some Loxophyllum species; form conspicuous layer in marginal fringe of cell, lacking only in anterior dorsal area where oral bulge is absent; stain heavily with silver carbonate, but not with protargol. Cortex thin, highly flexible, without special granules, e.g. mucocysts. Cytoplasm colourless, in central region of cell more or less densely filled, depending on food supply, with brightly shinning fat globules and food vacuoles; no special cytoplasmic crystals. Feeds on small and medium sized ciliates (Glaucoma scintillans, Cinetochilum margaritaceum, Colpidium colpoda) and probably also on bacteria and/or detritus. Moves slowly, glides with densely ciliated right side on flat substrates or crawls elegantly on and between detritus aggregations showing great flexibility and deformation body. General plan of somatic and oral infraciliature as in other members of order (Foissner 1984). In an old culture, most specimens had greatly reduced numbers of kineties, viz. 4-7 on right and 3-4 on left side, while body size was not markedly reduced. Right side densely ciliated, kineties with cilia about 7 um long succesively shortened along anterior half of perioral kinety 3 and in posterior region of cell, where some abut to right dorsolateral kinety and third perioral kinety. Right dorsolateral kinety very near to dorsal margin of cell, bears regular somatic cilia and fibrillar associates commences at anterior end of cell and curves around its posterior end. Left side more sparsely ciliated than right, its ciliature consists of somatic kineties, a brush kinety, and a dorsolateral kinety. Somatic kineties in cental third of cell on top of cortical crests, distinctly shortened anteriorly and posteriorly, cilia reduced to 1-2 um long stumps and about twice as widely spaced as on right side. Brush kinety in anterior third of body between leftmost somatic ciliary row and left dorsolateral kinety, about 4 um apart from dorsal margin of cell, consists of 30-50 very closely spaced dikinetids having 1-3 um long cilia in anterior third of cell and of closely spaced, nonciliated monokinetids in posterior portion ("tail"), which extends left of a flat cortical crest; anterior portion of brush on bottom of depression formed by anterior end of oral bulge, often fragmented, right fragments sometimes connected with crest kineties; cilia of dikinetids cylindroid to slightly inflated distally, anterior cilium usually slightly longer than posterior, length of cilia decreases from anterior to posterior; dikinetidal axis usually parallel to main body axis, rarely oblique or almost transverse, especially if anterior portion is fragmented. Left dorsolateral kinety very near dorsal margin of cell, extends along this whole length and is thus continuous with perioral kinety 1 at both ends, bears about 2 um long cilia and is thus easily distinguished from the almost adjacent right dorsolateral kinety which has regular (long) somatic cilia. Oral bulge surrounding almost entire cell, leaving blank only small area at anterior end of dorsal side, about 2 um high and thus difficult to recognized in the light microscope. Anterior end of bulge curved to left surface of cell, producing inconspicuos crest right of which brush kinety commences. Bulge surface patterned string-like, with small hemispherical structures between riffles, possibly tips of toxicysts. Nematodesmata very fine, originate from barren basal bodies of perioral dikinetids (see TEM section), recognizable only up to mid-body, indicating that functional mouth is much shorter than oral bulge. Perioral kinety 1 at left margin of oral bulge, merges into left dorsolateral kinety anteriorly and posteriorly, anterior half composed of regularly spaced dikinetids, posterior portion made of equidistantly spaced monokinetids; anterior basal body of dikinetids lighter stained than posterior one, bears about 2 um long, cylindroid ciliary stump; dikinetids orientated obliquely to kinety axis, i.e. parallel to main body axis, without kinetodesmal fibres in silver carbonate impregnated specimens. Perioral kinety 2 at right margin of oral bluge, composed of tightly spaced dikinetids, at least in anterior half, as indicated by distribution of nematodesmata; anterior or posterior basal body of dikinetids with regular, about 7 um long cilium; dikinetids orientated obliquely or almost transversely to main body axis, without kinetodesmal fibres in silver carbonated stains. Perioral kinety 3 right of and very close to kinety 2, ends indistinctly separate from right dorsolateral kinety, composed of monokinetids throughout; kinetids with normal long cilia and a conspicuous kinetodesmal fibres orientated more laterally than those of somatic kinetids, at least in anterior half. (ref. ID; 7355)

Comparison of descriptions of S. utriculariae

Our observations basically agree with those mentioned in the original description (Penard 1922) and the two redescriptions (Kahl 1931; Song and Wilbert 1989). Thus, we do not doubt the identification and conspecifity of all populations. However, some differences should be noted. Penard (1922) drew the anterior contractile vacuole near the dorsal margin and the posterior vacuole near the ventral side, whereas Kahl (1931) and Song & Wilbert (1989) definitely stated an opposite location, which agrees with our observations. Thus, it may be assumed that Penard's indication is a simple mistake, all the more so as he did not definitely describe the location of the vacuoles. Another difference concerns the extrusome which, according to Penard (1922), are elongated in the strongly flattened and slightly protruding oral area, whereas Kahl (1931) and Song & Wilbert (1989) found them to be of the same length over the whole perimeter of the cell, which matches our observations. Although the shape and size of the extrusomes are important species characteristics in gymnostomatid ciliates (Foissner 1984; Foissner et al. 1995), this differences cannot be weightened heavily because Penard (1922) never used oil immersion objectives and thus very likely could not ascertain the real length of the extrusomes in the thicker, opaque parts of the cell. Song & Wilbert (1989) redescribed S. utriculariae very briefly, but provided some elegant drawings which, however, do not give any indication of dorsolateral kineties. We suppose that Song & Wilbert overlooked them because their description contains also other unfortunate mistakes. They figure all oral kineties as being composed of dikinetids and the oral slit between perioral kineties 2 and 3. Both observations are clearly disproved by our data and literature evidence. (Bohatier and Njiner 1973; Foissner 1984; Foissner et al. 1995) (ref. ID; 7355)
  • Ultrastructure: The fine structure of the somatic kinetids of S. utriculariae is very similar, if not identical, to that of haptorids like Spathidium (Williams et al. 1981) and Enchelydium (Foissner et al. 1985). The second transverse microtubular ribbon was apparently overlooked in previous descriptions of pleurostomatids, but can be recognized in published micrographs of Loxophyllum meleagris ((Puytorac et al. 1975). Siroloxophyllum utriculariae is thus a ditransversal ciliate in the sense of Leipe & Hausmann (1989). The interpretation of the oral structures is more difficult. As concerns perioral kinety 1, our results agree with previous descriptions (Bohatier and Njine 1973; Puytorac et al. 1975), while the structure of perioral kineties 2 and 3 appears different in several respects. Whether these differences are genus specific or caused by interpretation problems needs further investigations. At least some data in Bohatier & Njine's (1973) paper appear doubtful, for instance that perioral kineties 2 and 3 lack cilia. In S. utriculariae they are ciliated and form the typical mane recognized earlier by Kahl (1931) in many pleurostomatids. A second problem is posed by the kinetodesmal fibre, which is, according to Bohatier & Njine (1973), associated with the posterior basal body of the dikinetids of perioral kinety 2. Our data show that it originates from the monokinetids of perioral kinety 3, which is more likely since the haptorid oral dikinetids generally lack a kinetodesma (Lipscomb and Riordan 1990). Perioral kinety 3 is very likely a specialized somatic kinety, analogous (because it apparently lacks nematodesmata) to the oralized somatic kinetids found in several haptorids (Foissner et al. 1988). A third problem concerns the species investigated by Bohatier & Njine (1973). Their figures doubtlessly show a Litonotus species, as indicated by the triads formed by the kinetids of perioral kineties 2 and 3, but very likely not L. quadrinucleatus which lacks, according to Dragesco & Njine (1971), perioral kinety 3 but has a conspicuous spica, indicating that it belongs to the genus Amphileptus (Foissner 1984). Unfortunately, Bohatier & Njine (1973) did not mention the source of their material. (ref. ID; 7355)

    Ecology

    This section is complication of the faunistic and ecological literature available on S. utriculariae. Few records are known, most are from running and stagnant freshwaters; those from mosses and soils in Germany (Wenzel 1953) and New Zealand (Stout 1958, 1961) are very likely misidentifications, because the species died in our cultures without forming permanent (resting) cysts, indicating that it cannot live in soil. Futhermore, we have never found it in the more than 1,000 soil and moss samples investigated during the last decade. Thus, all reliable records are from freshwaters of central and eastern Europe and Mexico (Sokoloff and Ancona 1937). It seems that S. utriculariae is a rare species, usually occurring with low abundance. Penard (1922) and Kahl (1926, 1931) found S. utriculariae between Utricularia weed in Geneva (Switerland) and Hamburg (Germany), respectively. Several records (Detcheva 1992; Enaceanu and Brezeanu 1970) are avaiable from the Danube river, where S. utriculariae lives in the periphyton of stones, and from oligosaprobic and mesosaprobic rivers, brooks and ponds in Germany (Buck 1961; Foissner et al. 1992), Bulgaria (Detcheva 1972, 1992) and Mexico (Sokoloff and Ancona 1937). Detcheva (1972) provides the following abiotic parameters from a single record in a beta-mesosaprobic river in Bulgaria: pH 7.7, 8 mg/L O2 (94% saturation), 3.6 mg/L biological oxygen demand (5 days), 12.6 mg/L chemical oxygen demand, 118 mg/L Ca2+, 24 mg/L Mg2+, 0.25 mg/L (NH4+)-N, 1.9 mg/L (NO3-)-N, 0.06 mg/L (NO2-)-N, 0.2 mg/L Fe2+, 0.2 mg/L Mn2+, 0.06 mg/L phenols. We found S. utriculariae infrequently and with low individual numbers in beta-mesosaprobic to alpha-mesosaprobic rivers near Munich, Germany (Foissner et al. 1992). It occurred more regulary and abundantly in the sludge of rapid gravity filters of some waterworks in this region; the abundance variations observed could be not correlated with specific biotic and process parameters (Foissner 1995). Siroloxophyllum utriculariae glides slowly and elegantly in the periphyton of natural and artificial substrates. Like other members of the group it is a predator. However, detailed observations from natural populations are not available. In cultures it feeds on small to medium-sized ciliates, like Glaucoma scintillans and Colpidium colpoda, which are apparently quickly digested because the cells are usually rather hyaline and rarely contain identifiable prey residures; bacteria and/or organic detritus are probalby also ingested. Biomass of 10E6 medium-sized (150x50x20 um) cells about 90 mg (Foissner et al. 1995). Sladecek et al (1981) and Wegl (1983) consider S. utriculariae as a excellent indicator of beta-mesosaprobic conditions and provide the following valency spectrum: beta-mesosaprobic; oligosaprobity (o)=1, beta-mesosaprobity (b)=8, alpha-mesosaprobity (a)=1, indication weight (I)=4, saprobity index (SI)=2.0. However, the data available indicate that the oligosaprobic proportion should be increased in the valency; but this needs further investigations (Foissner et al. 1995). (ref. ID; 7355)