Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Phyllomitus

Phyllomitus Stein, 1878 (ref. ID; 4656)

[ref. ID; 1618]
Oval; highly plastic; cytostome large and conspicuous; two unequal flagella, each originates in a blepharoplast; fresh water or coprozoic. (ref. ID; 1618)

[ref. ID; 5694]
Free-living heterotrophic flagellates. (ref. ID; 5694)
  1. Phyllomitus amylophagus Klebs, 1892 (ref. ID; 4656)
  2. Phyllomitus apiculatus Skuja, 1948 (ref. ID; 4715)
  3. Phyllomitus undulans Stein (ref. ID; 1618, 3497)

Phyllomitus apiculatus Skuja, 1948 (ref. ID; 4715)

Descriptions

In culture, Phyllomitus shows a significant moving activity. The swimming trajectory in this flagellate is a zigzag. The onward movement of Phyllomitus is accompanied by body oscillations. After a contact with prey, Phyllomitus stops and ingests the prey as a whole in 5-20s. The cytostome extends considerably during this act. At the very movement of being engulfed, the prey's flagella are still moving. Sometimes the predator's recurrent flagellum is seen to push the prey into the cytopharynx by spiral movements. After ingestion of several prey cells the predator undergoes binary longitudinal fission. If food is insufficient, Phyllomitus diminishes in body size and dies. The predatory mode of feeding of this organism is obligatory (Mylnikov 1983). Cannibalism has not been observed. No cysts have been found. The two heterodynamic flagella emerge from a depression, the flagellar pocket. During swimming one flagellum (9-11 um long) is usually directed forward and performs rowing movements. The second flagellum (12-16 um) is directed backwards; at the moment of movement cessation, it spirally winds around the flagellate's body. The flagella become thinner at their distal ends. Thin mastigonemes are observed along the entire length of the flagella. The mastigonemes are 200-250 nm long and 4.0-4.5 nm thick. The flagellar kinetosomes are oriented parallel to each other. Cross-striated filaments have not been found. The kinetosomes are interconnected by an amorphous osmiophilic material. The flagellar basal plate rises over the cell surface by 190-230 nm. The flagellar surface is covered with the same layer of glycocalyx as the entire cell. Both flagella possess paraxial rods emerging at the level of the basal plate. Several bands of microtubules starting near the kinetosomes have been found in the cell. Two bands, consisting of 3-5 microtubules each, run from the kinetosomes to the rear of the body. The third S-shaped band, consisting of 6-7 microtubules, underlines the lateral wall of the flagellar pocket and runs in a groove. At the anterior end of the body it bends backwards and passes under the cytopharygeal membrane, accompanying the cytopharynx along its entire course. At the bending point this band forms a small bulge on the body surface, which carries a bundle of thin sinuous filaments. Near the S-shaped band of microtubules, a microtubular prism (terminology of Burzell 1975) consisting of three rows of 6, 8 and 9 microtubules, and an osmiophilic amorphous structure (the spur) have been detected. The spur accompanies the cytopharynx along its entire course. The cytopharynx starts at the anterior end as a small aperture and passes as a narrow tube parallel to the flagellar pocket. Its maximum length is 4 um. The cytopharyngeal surface carries thin treads similar to flagellar mastigonemes. The narrow end of the cytopharynx is detected at the nucleus level. Since profiles of the flagellar pocket and cytopharynx are frequently observed on sections simultaneously, it is possible to draw a conclusion that these two depressions are not connected with each other. The Golgi apparatus (dimensions 0.3-0.5x1.0-1.2 um) and the endoplasmic reticulum are of the usual structure. The contractile vacuole is located between the cytophaynx and flagellar pocket. During diastole stage, the contractile vacuole and the flagellar pocket are separated with only a thin partition. The contractile vacuole probably discharges its contents into the flagellar pocket. Food vacuoles lie most frequently in the posterior part of the body. Remnants of prey or bacteria have not been observed inside them. This can be explained by the fact that Phyllomitus was fixed at stationary growth phase and was not feeding. The nucleus, 1.8-2.2 um in diameter, is situated near the flagellar kinetosomes. The nucleolus consists of several lobes, and the peripheral lobes surround the central part of the nucleolus. The chromatin is inconspicuous. It is possible, however, the peripheral lobes consist of the chromatin. The nuclear pores can be noticed on several sections. No stages of mitosis have been observed. The whole cell of the flagellate is permeated by a mitochondrion with lamellar cristae. The maximum length of the mitochondrion is 5-6 um, the width being 2 um. Besides the cristae, osmiophilic bodies and matrix are observed in the mitochondrion. A typical kinetoplast has not been found. However, parts of the mitochondrion with condensed fibrous material resembling DNA have been noted on a number of sections. Usually such kinetoplast-like structures are found in degraded or dead individuals. The diameter of this structure is equal to 1.5-2.0 um. It has not been possible to detect mitochondrial DNA using Feulgen's method. Usually one mitochondrial profile is seen on sections of the anterior body end, and several profiles at the rear end. It is possible that the mitochondrion is branching near the rear end. At the anterior end there are peculiar trichocyst-like structures, here called mucocysts (according to Hovasse and Mignot 1975). The mucocysts are usually arranged in rows near the cytopharynx and in the lip. There are 7-11 mucocysts in one rows. Under the light microscope the mucocysts are seen after staining with haematoxylin or when using interference optics. A mucocyst consists of an outer tube, 120-150 nm in diameter and 2.5 um long, and an inner amorphous tube 100 nm in diameter. A thread is seen inside the mucocyst. Between the tubes there is a bright zone. It has not been possible to observe the process of liberation of the mucocysts. However, numerous extruded mucocysts have been fixed near the cells. They consist of a reticulate tube without inner contents. The mesh size of the reticulum is 25 nm. The diameter of the reticulate tube is 150-200 nm. Thus, the diameter of the mucocysts increases after the liberation. The mucocysts are formed in the cisternae of the Golgi apparatus. Extruded mucocysts are often seen inside the food vacuoles. Within the cell there are also symbiotic bacteria, 450 nm long and 300 nm in diameter. It has been possible to observe division of these bacteria in the cytoplasm. (ref. ID; 4715)

Remarks

The microtubular prism in Phyllomitus is similar to that in Bodo curvifilus and B. designis (Burzell 1975; Eyden 1977). The spur emerging from the kinetosome in Phyllomitus is also found in the euglenoid alga Isonema nigricans (Schuster et al. 1968). Eyden (1977) thinks that the microtubular prism is probably homologous to the band of 20 microtubules in Bodo spp. (Brooker 1971) and to the quadritubular band in Cephalothamnium cyclopum (Hitchen 1974). The mastigonemes of Phyllomitus are similar to those in Pleuromonas jaculans (Karpov and Zhukov 1983) but are less conspicuous than the mastigonemes in Bodo saltans and B. caudatus (Brooker 1971). The nucleus, Golgi apparatus, contractile vacuole, and endoplasmic reticulum in Phyllomitus are typical of the kinetoplastids. One of the interisting features in Phyllomitus is the absence of a typical kinetoplast. Kinetoplast-like structures are found rarely and only in a few individuals. Probably such an organisation of the mitochondrion is more like that the bodonid Ichthyobodo necator (Joyon and Lom 1969). Osmiophilic bodies in the mitochondrion of Phyllomitus are known to occur in the bodonid Spiromonas angusta (MacDonald and Darbyshire 1977). The latter has other elements of morphology similar to those in Phyllomitus: heterodynamic flagella, cytopharynx with underlining microtubules, subpellicular microtubules, and a bundle of filaments near the cytopharynx opening. Moreover, the cytopharynx opening in S. angusta is situated at the anterior end of the body, like in Phyllomitus. Recently, Steinberg et al. (1983) noted staining organelles at the anterior end of the body in Phyllomitus. Our electron micrographs show the structure of these organelles. Similar organelles are known in many Protozoa: ciliates, dinoflagellates, chloromonads, euglenomonadids (Hausmann 1978), but not in the bodonids. An especially great similarity in size and shape is observed between the mucocysts of Phyllomitus and those in euglenoid algae Isonema nigricans (Schuster et al. 1968) and Entosiphon sulcatum (Mignot and Hovasse 1973). The tubular wall of these organelles has a reticulate structure. They are filled with amorphous material. (ref. ID; 4715)

Measurements

The body length is 8-15 um, width 3-6 um. (ref. ID; 4715)

Phyllomitus undulans Stein (ref. ID; 1618, 3497)

Descriptions

Ovoid; trailing flagellum much longer than anterior one; stagnant water. (ref. ID; 1618)
The cell is oblong and slightly compressed. The flagella come out from an oral depression at the anterior lateral portion, of which the swimming flagellum is shorter than the body containing few reflexible granules, while the other trailing is twice as long as it. (ref. ID; 3497)

Measurements

21-27 um long. (ref. ID; 1618)
Length 11-12 um; breadth 6-7 um. (ref. ID; 3497)