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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Trachelolophos

Trachelolophos Foissner & Dragesco, 1996 (ref. ID; 7362 original paper)

Ciliophora: Karyorelictea (ref. ID; 7362)

[ref. ID; 7362]
Diagnosis; Trachelocercidae Kent (1880-1882) it conspicuous ciliary tuft in head (oral) cavity and simple, uninterrupted circumoral and bristle kinety, each composed of single row of dikinetids. (ref. ID; 7362)
Remarks; Following a note from Kahl (1933), Delphy (1939) hastily split trachelocercid karyorelictids into four genera, viz. Trachelocerca (distal end of tail curved), Gruvelina (whole tail extends in main body axis), Nephrocerca (with contractile vacuole), and Protrichophora (with mucocysts; invalid because no type species was fixed). Later, Dragesco (1960) split the trachelocercids again using, however, the absence (Trachelocerca)/presence (Tracheloraphis, Trachelonema) of a glabrous stripe and it relative width as sole characters. Unfortunately, the features used by Delphy (1939) and Dragesco (1960) are highly questionable because, e.g., all trachelocercids have a glabrous stripe, although it is inconspicuous in some species and thus difficult to recognize without silver impregnation. Likewise, a contractile vacuole is lacking in all true trachelocercids, and whether or not the distal end of the tail is slightly curved often remains ambiguous and is at best a species character. Later investigators did not improve this situation, but simply followed Dragesco's view and moved species from one genus to the other. The characters we apply to distinguish trachelocercid genera are based on the somatic and oral infraciliature. This complication uses results from the present and former (Dragesco & Dragesco-Kernies 1986; Foissner 1996) investigations as well as unpublished material. Trachelolophos is apparently near Trachelocerca, differing in the peculiar tuft of cilia within the oral cavity. However, if the tuft is considered as a highly modified brosse, Trachelolophos would be more closely related to Tracheloraphis than to Trachelocerca. This needs to be clarifed by ontogenetic studies. The two species of Trachelolophos described in this paper are not unique. Meanwhile, we found at least two other distinct species (with few nuclei near mid-body), which will be described later. (ref. ID; 7362)
[Bristle kinety]: The ciliation and arrangement of the bristle kinety suggest that it is a single ciliary row surrounding the glabrous stripe. This would certainly be an unusual pattern for a somatic ciliary row! However, our interpretation is supported by a detailed in vestigation of Cryptopharynx and Apocryptopharynx, loxodid karyorelicteans with a left lateral (bristle) kinety extending along the entire cell margin (Foissner 1996). This kinety, whose course can be easily followed due to the broadly rounded ends of the organisms, has the same ciliation pattern as the bristle kinety of T. gigas. Other interpretations cannot, however, be completely ruled out in the absence of ontogenetic evidence, viz. that the bristle kinety is composed of two kineties, i.e. a right and left branch, with opposed kinetids, or of many small kineties originating from the anterior and/or posterior end of those somatic kineties which abut to the glabrous stripe. The last mentioned possibility is unlikley because the kineties in the right posterior region of the organism have the anterior basal bodies ciliated, whereas the posterior basal bodies are ciliated in the neighbouring portion of the bristle kinety. (ref. ID; 7362)
Etymology; Composite of the Greek nouns "trachelos" (neck) and "lophos" (tuft). Maculine gender. (ref. ID; 7362)
Type species; Trachelolophos gigas n. sp. (ref. ID; 7362)
  1. Trachelolophos filum (Dragesco & Dragesco-Kerneis, 1986) Foissner & Dragesco, 1996 (ref. ID; 7362 redescribed paper)
  2. Trachelolophos gigas Foissner & Dragesco, 1996 (ref. ID; 7362 original paper)

Trachelolophos filum (Dragesco & Dragesco-Kerneis, 1986) Foissner & Dragesco, 1996 (ref. ID; 7362 redescribed paper)

History and identification

Dragesco & Dragesco-Kerneis (1986) briefly described a new tracelocercid, Tracheloraphis filum, from a saline, temporary pool in Benin, Africa. It is distinguished from the congeners by a trichocyst bundle in the oral cavity, a very narrow glabrous stripe, and a nuclear apparatus usually consisting of several pairs of macronuclei, each with an interposed micronucleus. Dragesco & Dragesco-Kerneis (1986) found eight specimens, but the type slide contains only four cells, whose reinvestigation showed that they match the original description, which is, however, rather incomplete due to the poor quality of the impregnation. For instance, only the anterior portion of the bristle kinety was recognized and the ciliary tuft in the oral cavity was misinterpreted as trichocyst bundle. The population found at Roscoff matched the type specimens in all respects, except for a higher number of somatic kineties, viz. 26-35 (average=30) vs. 20-24 (average=22). This difference is considered as insufficient for separating the two populations at species or subspecies level because very little is known about variability in trachelocercids. (ref. ID; 7362)

Redescription

Like Dragesco & Dragesco-Kerneis (1986), we found only few specimens and did not observe live cells. One of the seven specimens studied is distinctly larger (1,100 um) and has more nuclei (30 macronuclei and 20 micronuclei) than the other cells. However, variation in the nuclear apparatus is great (6-24 macronuclei) also in the other specimens and thus the large individual very likely belongs to the same species as the other cells. (ref. ID; 7362)

Remarks

Trachelolophos filum and T. gigas differ only in morphometric characteristics (size, number of kineties and dikinetids in ciliary tuft, etc.). The structure of the infraciliature is identical. Thus, we desist from a complete description, which would be a repetition of that given for T. gigas, and refer to the detailed figures and figure explanations. In the large specimens mentioned above and in one other specimen the cilia of the oral ciliary tuft form distinct rods, reminiscent of the "trichocysts" described by Dragesco & Dragesco-Kerneis (1986). A detailed analysis of these and the type specimens showed that the rods are actually formed by two closely spaced cilia, which, when intensely stained, appear as thick rods. Faintly impregnated cells show the tuft to be composed of closely spaced dikinetids having only one basal body ciliated, as in T. gigas. Thus, Tracheloraphis filum Dragesco & Dragesco-Kerneis (1986) is transferred to the genus Trachelolophos: T. filum (Dragesco & Dragesco-Kerneis, 1986) n. comb. (ref. ID; 7362)

Type material

We have deposited Dragesco & Dragesco-Kerneis' type slide of T. filum in the Oberosterreichische Landesmuseum in Linz (LI), Austria, accession number: 11/1995. Two voucher slides of the population described in this paper have been deposited at the same locality, accession numbers: 12-13/1995. Relevant specimens are marked by a black ink circle on the cover glass. (ref. ID; 7362)

Trachelolophos gigas Foissner & Dragesco, 1996 (ref. ID; 7362 original paper)

Diagnosis

In vivo about 2,000x50 um. Neck cylindroid, distinctly separate from flattened, parallel-sided trunk; tail long but indistinctly separate from trunk. 17-33 (average=25) macronuclei forming strand in trunk. Cortex 3-5 um thick, gelatinous, without conspicuous granules. 26-30 (average=28) ciliary rows on neck, 52-71 (average=62) on trunk; glabrous stripe narrow, corresponds to area occupied by one kinety and two interkinetal spaces. Oral ciliary tuft composed of 33-50 (average=44) cilia. (ref. ID; 7362)

Descriptions

All observations are from field material. Thus, it cannot be excluded that different species were mixed, although we excluded specimens which deviated in at least one prominent character. Size in vivo about 2,000x50 um, less distinctly contractile than many other trachelocercids, size and shape thus comparatively well preserved in protargol slides. Shape rather constant, prolate fusiform; head trumpet-shaped and up to 50 um wide, neck comparatively short and cylindroid, widens abruptly to long, parallel-sided, distinctly (about 2:1) flattened trunk gradually narrowing to long tail with distal end pointed and slightly curved. Macronuclei globular to distinctly (up to 2:1) ellipsoid, with many small nucleoli; not in capsules but individually arranged in trunk, left of cell median, forming conspicuous strand. Micronuclei globular, near and between macronuclei, stain bluish with methyl green-pyronin, like macronuclear nucleoli, indicating presence of DNA. No contractile vacuole. Cortex conspicuous, i.e. pellicle underlain by 3-5 um thick, gelatinous layer distinctly separate from granular cytoplasm, lacks specific granules and/or mucocysts, forms columnar blisters (tubercles) in contracted specimens. Cytoplasm colourless, cells appear greyish at low (40x) magnification, contains numerous 5-10 um sized food vacuoles with granular content, many 1-3 um sized fat globules and many about 2x1 um sized crystalline (?) inclusions slightly accumulated in head, which is thus a little darker than the rest of the cell. Movement like other large trachelocercids, i.e. elegantly gliding and winding between sand grains and organic debris. (ref. ID; 7362)
  • Somatic infraciliature: The surface of T. gigas is densely ciliated, leaving blank only a narrow zone, the glabrous stripe, exending along the whole body length near the median of the left side. The cilia, which are rather stiff and can be spread, are about 12 um long and arranged in longitudinal rows, which are distinctly separate from the circumoral kinety and extend between flat cortical crests. The ciliary rows are gradually shortened anteriorly in the neck region left of the glabrous stripe and posteriorly, where the body narrows to the tail, at both sides of the stripe. In other words, an anterior secant system is formed on the left surface of the neck, where many kineties abut to the left branch of the bristle kinety. Thus, the head, neck, and tail have only about half the kinety number present on the trunk. The ciliary rows neighbouring the right branch of the bristle kinety are unshortened anteriorly, i.e. extend parallel to the glabrous stripe; furthermore, the ciliary rows are slightly more widely spaced on the right than on the left surface of the cell. The entire infraciliature consists of dikinetids which, however, have a highly specialized ciliation and fibrillar system. The dikinetids are rotated about 20-30 degrees counter-clockwise of the kinety axis and associated with conspicuous, overlapping post-ciliary microtubule ribbons which originate from the posterior basal bodies of the dikinetids and form a thick, faintly impregnated postciliodesma right of each ciliary row. A thin, sharply impregnated fibre, possibly a myoneme or subkinetal microtubule ribbon (Raikov & Kovaleva 1995; Raikov et al. 1975), extends close to the left of each ciliary row. Both basal bodies of the dikinetids are ciliated in the main portion of the cell. The posterior cilium is lacking in about five dikinetids at the anterior end of the head kineties. These kinetids are more narrowly spaced than those on the trunk, and associated with distinct nematodesmal fibres originating from the posterior, nonciliated basal bodies. The nematodesmata from the condensed kinetids unite to form small bundles extending almost parallel to the cell surface. Similar fibres originate from the neck dekinetids which, however, have basal bodies ciliated. These fibres do not form bundles and extend obliquely posteriad to the neck midline. The nematodesmata-bearing kinetids of the head and neck region are thus oralized somatic dikinetids as defined by Foissner & Foissner (1988). The posterior cilium is also lacking in three to ten dikinetids at the posterior end of the kineties, i.e. around the secant system of the tail region. The glabrous stripe extends along the whole length of the body and is very narrow, i.e. corresponds to an area occupied by about one kinety and two interkinetal spaces. It is slightly depressed, especially in the head region, and bordered by the bristle kinety which consists, like the ordinary ciliary rows, of dikinetids. However, the bristle kinety is easily distinguished from the ordinary somatic kineties because its dikinetids are more irregularly and loosely arranged and either lack or have very inconspicuous postciliary microtubule ribbons too small to be recognized with the light microscope. Furthermore, the bristle kinetids have a unique ciliation, most parsimoniously explained with the assumption that they belong to a single kinety exending along the glabrous stripe margins, quite similar to the left lateral kinety of the loxodids (Foissner 1996). The bristle kinety commences subapically at the right margin of the glabrous stripe, extends posteriorly, then anteriorly at the left, to end up at the right margin again. The dikinetids of the right posterior portion of the bristle kinety have the posterior basal bodies ciliated, whereas the anterior basal bodies are ciliated in its left and right anterior portion. Both ends of the bristle kinety are very close together subapically at the right margin of the glabrous stripe. Thus, there is a point where the ciliation of the dikinetids is diametrically, i.e. by 180 degrees opposed. Frequently, the dikinetids of the anterior portion are more irregularly and more obliquely arranged than those farther behind; furthermore, isolated dikinetids and/or minute dikinetidal fragments occur between the arch of the bristle kinety and the circumoral kinety. There is thus a slight but distinct variability in the anterior region of the bristle kinety and, in fact, none of the specimens studied agreed completely in this respect. A honeycombed structure impregnated very clearly in the cortex of a regenerating specimen which had lost the posterior body half. The pattern was less distinct in the glabrous stripe. (ref. ID; 7362)
  • Oral infraciliature: The head, which bears the oral apparatus, is trumpet-shaped when fully extended and cylindroid when contracted. Its anterior end bears an inconspicuous, i.e. about 3 um thick, hyaline oral bulge at the base of which the circumoral kinety extends. The centre of the bulge and head is hollowed to an about 13 um deep oral cavity. On the bottom of the cavity, slightly of centre (possibly approaching the bristle kinety), is a small eminence covered with a roundish patch of about 44 disordered dikinetids each having only one basal body ciliated. The cilia of this patch are about 15 um long, mobile, and form a conspicuous tuft extending slightly beyond the oral bluge and recognizable also in live specimens. The circumoral kinety consists of dikinetids having only new basal body ciliated, possibly the posterior. The kinety appears to be composed of about 10 segments separated by inconspicuous spaced one to two dikinetids wide. The basal bodies of the dikinetids are arranged in zigzag and associated with nematodesmata forming an oral basket together with the nematodesmal bundles originating from the oralized somatic dikinetids at the anterior end of the somatic kineties. (ref. ID; 7362)

    Comparison with related species

    No other species with a tuft of cilia in the oral cavity has been described. However, this attribute is not easily recognized and most trachelocercids have been only superficially studied. If we disregard this special feature, three species remain which resemble T. gigas. Tracheloraphis discolor Raikov, 1962 is similar to T. gigas in size, shape, glabrous stripe and kinety number, but possesses 6-17 nuclear capsules each with four macronuclei and two micronuclei, which is highly dissimilar to the simple nuclear configuration of T. gigas, Tracheloraphis dogieli Raikov, 1957 is similar in size, shape, nuclear apparatus and kinety number, but has a broad, conspicuous glabrous stripe. Trachelocerca multinucleata Dragesco, 1960 is similar to T. gigas in shape, nuclear apparatus and glabrous stripe, but is smaller (1,000-1,300 um), unflattened, has more than 100 ciliary rows, and fine trichocysts in the centre of the oral bulge. Possibly, cilia are mistaken for trichocysts (see T. filum); if so this species would belong to Trachelolophos. Likewise, T. discolor and T. dogieli could belong to the new genus because they have a distinct oral cavity. (ref. ID; 7362)

    Etymology

    'gigas' (giant) refers to the large size of the organism. (ref. ID; 7362)

    Type location

    Mesopsammon of French Atlantic coast at Roscoff, W4 degrees, N48 degrees 50'. (ref. ID; 7362)

    Type specimens

    One holotype and one paratype of T. gigas as two slides of protargol (Wilbert technique) impregnated specimens have been deposited in the collection of microscope slides of the Oberosterreichische Landesmuseum in Linz (LI), Austria, accession numbers: 9-10/1995. Relevant specimens are marked by a black ink circle on the cover glass. (ref. ID; 7362)