Trachelotractus
Trachelotractus Foissner, 1997 (ref. ID; 2130)
[ref. ID; 2130]
Helicoprorodontidae with few (two) parallel brush kineties spiralling around cytopharyngeal opening in single turn. Brush subapical, composed of ciliated dikinetids. Head extrusomes in single circumpharyngeal bundle attached to peribuccal ridge. (ref. ID; 2130)
Etymology; Composite of the Greek noun trachelos (neck) and the Latin noun tracuts (extension), referring to the similarity with Trachelocerca in general appearance and contractility, Masculine gender. (ref. ID; 2130)
Type species; Trachelocerca entzi Kahl, 1927 (ref. ID; 2130)
- Trachelotractus entzi Kahl, 1927 (ref. ID; 2130 redescribed paper)
Trachelotractus entzi Kahl, 1927 (ref. ID; 2130 redescribed paper)
Descriptions
Extended about 100x35 um; contracted about 300x50 um. Vermiform, head globular with crown-like peribuccal ridge, distinctly set off from cylindroid neck which gradually widens to trunk. About 150-600 macronuclei. On contractile vacuole in posterior end. Three types of rod-shaped extrusomes, i.e. long (35 um) and short (7 um) toxicysts in head and trunk, and minute (<1 um) mucocysts in cortex. An average of 28 ciliary rows on trunk and 20 on head. Brush consisting of two rows indistinctly separate from respective somatic kineties. (ref. ID; 2130)
Redescription
Largest, possibly fully extended specimens up to 1300 um and about 35 um wide. Vermiform with conspicuous, globular dark head distinctly set off from narrowed, greyish neck trunk cylindroid, brownish in dissecting microscope, gradually narrowed posterior but not tail-like. Head globular to pyriform, about as wide as trunk, black at low magnification because packed with highly refractile, 1-3 um sized fat globules and 1-2 um sized irregularly shaped granules different from he ellipsoidal inclusions found in many trachelocercids; peribuccal ridge circular, rather flat and with some minute processes, contains tightly packed extrusomes forming conspicuous core around cytopharyngeal basket, respectively, in central position of head. Very flexible and contractile fully contracted specimens cylindroid and about 300 um long; contraction very likely due to fibre (myoneme), rarely impregnated with protargol, located in small ridge left of each ciliary row, rather slow, length and shape of cell thus comparatively well preserved in protargol slides. Macronuclei small, globular to slightly ellipsoidal, distributed throughout body, exact number and micronuclei difficult to ascertain because of many similar sized cytoplasm inclusions, 300-600 nuclei seem to be common, with possibly type to 100 in largest cells. Contractile vacuole distinct, in rear end with single excretory pore in centre of posterior pole. Two size-types, 25 um and 7 um long, of thin, rod-shaped extrusomes in peribuccal ridge and scattered throughout cytoplasm singly and in large bundles, never attached to somatic cortex, unlike in Helicoprorodon. Long extrusomes usually curved and/or wrinkled in protargol slides, those attached to peribuccal ridge often completely or partially extruded providing cells with conspicuous apical beard; if completely extruded, head centre appears more pale than head margin and neck, where the nematodesmata of the oralized somatic kinetids extend. Cortex conspicuous because ornamented and forming about 2 um thick, vitreous layer sharply separated from granular cytoplasm, contains many minute (about 0.3x0.15 um) granules (mucocysts?) irregularly arranged in broad stripe left of ciliary rows; ornamented by small ridges extending left of each ciliary row and laterally between ciliary rows, lateral ridges especially pronounced in contracted specimens whose cortex is distinctly wrinkled. Cytoplasm colourless, contains many 1-5 um sized fat globules, innumerable 3x2 um sized ellipsoid inclusions, and many small (7-20 um long) diatoms; whether diatoms were actively ingested or contained in prey organisms has been not observed. Glides and winds elegantly between sand grains and organic debris. Surface very densely ciliated, cilia about 8 um long and arranged in longitudinal rows (kineties) becoming more or less distinctly spiral in contracted cells; about on third of kineties shortened in head and neck region and subterminally in posterior body portion, abridgement occurs over whole perimeter and without regularly, thus no secant system in formed, unlike in trachelocercids. Two kineties subapically specialized to distinct (dorsal) brush consisting of paired basal bodies (dikinetids) having about 4 um long, rather stiff cilia; brush kineties posteriorly not distinctly separated from their respective somatic kineties because of rather large zone where brush dikinetids irregularly alternate with somatic monokinetids; at least one brush kinety continues apically and curves around cytopharyngel opening, thus most ciliary rows abut to brush kineties. Two kinds of somatic monokinetids, viz. normal ones having a distinct postciliary microtubule ribbon in trunk, and oralized somatic kinetids having not only a postciliary microtubule ribbon but also a distinct nematodesma in head and neck region; nematodesma about 30 um long, those of head kinetids almost parallel to cell surface, those of neck obliquely extending to neck midline; postciliary microtubuler ribbons of neighbouring kinetids overlap and thus form conspicuous postciliodesma close to right of each kinety. Oral apparatus and infraciliature simple, in centre of apical end. Pharyngeal basket conical with bulbous anterior portion, about as long as head, composed of two distinct zones, viz. an outer lightly and an inner heavily impregnated region, sometimes curved loop-like or bifurcate; outer region very rarely spread fan-like. Pharyngeal opening surrounded by few dikinetids possibly belonging to anterior ends of brush kineties; details, however, difficult to recognize because minute and well-oriented apical views were not obtained due to the vermiform shape of the organism. (ref. ID; 2130)
Notes
T. entzi was first described by Entz (1884) as Trachelocerca phoenicopterus Cohn, 1866. However Entz (1884) obviously mixed at least three species, viz. T. phoenicopterus Cohn, 1866, T. entzi Kahl, 1927 and Lagynus sulcatus Gruber, 1888. Kahl (1927), who recognized Entz's mistake, provided a very detailed description of T. entzi, which largely agrees with my observation. Thus, there can be no doubt as to the identification. There is only one significant difference, viz. the number of kineties, about 20 according to Kahl (1927) and 25-40 in my specimens, which matches the value ("about 30") observed by Dragesco (1960). Thus, it is reasonable to assume that Kahl (1927), not having the advantages of silver impregnation, underestimated kinety number. Interestingly, I also underestimated the number of kineties in live specimens, i.e., recorded, very much like Kahl (1927), ("about 20 ciliary rows") in my notebook. (ref. ID; 2130)
Occurrence and ecology
T. entzi has been reported from littoral sands in Italy (Entz 1884), Germany (Bock 1952; Kahl 1927, 1928), France (Dragesco 1960, present study), England (Hartwig and Parker 1977), the Black Sea (Petran 1967) and the Caspian Sea (Agamaliew 1983). It colonizes fine and coarse sands (Bock 1952) and even saprobic sites (Dragesco 1960). Biernacka's (1963) report from the Polish sea coast is very likely based on a misidentification because the specimens lacked a contractile vacuole. (ref. ID; 2130)
Measurements
Great variation has been reported in body length [300-1000 um (Kahl 1927), 200-900 um (Dragesco 1960), up to 1300 um (this study)], body shape [club-shaped (Dragesco 1960), cylindroid-fusiform (Kahl 1927, this study)] and number of macronuclei [several hundreds (Kahl 1927), 150-200 (Dragesco 1960, about 300-600 (this study)], indicating that T. entzi could be a complex of different species However, size and shape are very difficult to ascertain in this species because of its high contractility; more systematic measurements, using video microscopy, are required. (ref. ID; 2130)