Phalansterium
Phalansterium Cienkowsky (ref. ID; 5731) or Cienkowski (ref. ID; 1618)
[ref. ID; 1618]
Small, ovoid; one flagellum and a small collar; numerous individuals are embedded in gelatinous substance, with protruding flagella; fresh water. (ref. ID; 1618)
[ref. ID; 5694]
Circumscription; Heterotrophic flagellates, forming colonies with cells embedded in an organic globular matrix, a single apical flagellum with tight-fitting continuous cytoplasmic collar. (ref. ID; 5694)
Ultrastructural identity; Mitocondria with tubular cristae, cells with a single apical flagellum with single basal body, anchorage involving concentric rings, which give rise to radiating microtubules. Well-developed dictyosomes associated with basal body. Flagellum with mucus but otherwise without hairs, scales, or other excrescences, no paraxonemal rods. (ref. ID; 5694)
Synapomorphy; Tubulocristate protist with single apical flagellum anchored by a radially symmetrical array of microtubules. (ref. ID; 5694)
Composition; One genus, several species. (ref. ID; 5694)
Reference; Hibberd 1983. (ref. ID; 5694)
- Phalansterium consociatum (Fresenius) Cienkowsky, 1870 (ref. ID; 6733) reported year? (ref. ID; 5731)
Syn; Monas consociata Fresenius, 1858 (ref. ID; 6733)
- Phalansterium digitatum Stein (ref. ID; 1618, 5731)
- Phalansterium intestinum Cienkowsky, 1870 (ref. ID; 5731)
- Phalansterium solitarium (ref. ID; 4944)
Descriptions
Oval; colony dendritic; fresh water among vegetation. (ref. ID; 1618)
[ref. ID; 5731]
Light microscopy: The structure of this organism agrees with the excellent light microscope description by Skuja (1964) and new data are included here mainly to form a basis for the EM obsevations. The gelatinous colonies of P. digitatum were arbusculate in 3 dimensions though the narrow proximal extremity could usually be seen only when they were flattened in a favourable plane. The colonies are formed of granular branching tubes and most of those studied consisted of about 32 cells, the result of 5 dichotomies. The spherules embedded in the gelationus matrix of the colony are 1.5-2.0 um in diameter and brownish in colour. The extreme end of each tube contains 1 or 2 flagellate cells, each of which measures 18-25x6-8 um. Delicate cytoplasmic strands can sometimes be seen extending from the posterior ends of the cells into the tube containing them. Each cell bears a single terminally inserted flagellum about twice as long as the cell, the proximal 15 um of which is thicker than the remainder and surrounded by a narrow collar-like prolongation of the anterior end of the cell 4-6 um long. The flagella beat rather stiffly with a flicking motion, and not a wavelike beat; the proximal 15 um always remains stiff and immobile, part lying within the collar and part within the mucilaginous matrix. Each cell contains a more or less centrally situated nucleus about 4 um in diameter containing a single nucleolus; two posterior contractile vacuoles which form by the coalescence of several smaller vacuoles; and spherical bodies of a similar diameter to the spheres in the branches of the colony. (ref. ID; 5731)
Electron microscopy: The cells are naked and rougly circular in cross-section and the anterior end is extended into a tapering tubular collar about 500 nm thick which surrounds the proximal end of the flagellum The single flagellum thus arises from the base of a deep pocket which widens at its proximal end into a chamber over 2 um diameter. Lightly staining fibrous-resticulate material, probably mucilage, fills the gap between the flagellum and the collar, and this substance appears as strands extending radially from the axoneme at the extreme proximal end of the flagellar pocket. The colony matrix is formed of identical fibrous-reticulate material in which are embedded the spherical granules. The mucilage layer extends laterally over 5 um from the cell and about 2.5 um distally, the flagellum emerging through a funnel-shaped opening. The spherules are more or less evenly distributed through the mucilage, though there are fewer at the exterme distal ends of the branches. They are all about 1.5 um in diameter though their boundaries are often indisctinct. The matrix of the spherules appears fibrous-reticulate with interspersed denser granules. The nucleus is roughly spherical and is always distant from the flagellar base and Golgi body. It contains a single spherical nucleolus and small chromatin bodies some of which appear very dense. There is no microbody associated with the posterior part of the nucleus. The single Golgi body lies immediately beneath the flagellar base and partly surrounds the fibrous flagellar root. It is approximately 2.0 um in diameter and consists of 15-17 cisternae. The proximal 4-6 cisternae an the edges of some of the more distal ones are distinctly swollen and contain lightly staining fibrous material. The edges of the distal closely adpressed cisternae are highly reticulate. The most distal cisterna, lying next to the rhizoplast, sometimes appears in section as an irregular row of vesicles, this probably indicating a reticulate structure. This, and not the proximal cisterna, appears to be the forming face of the Golgi body, vesicle maturation always proceeding proximally. Evidence that a small vesicle has recently fused with the cell membrane can sometimes be seen in sections at this level, and they have also been found elsewhere on the cell membrane. This is probably the method by which the mucilage forming the colony matrix is secreted. Mitochondrial profiles are relatively small and appear randomy distributed; the cristae are tubular in shape. Rough ER cisternae are also randomly distributed and the cytoplasm is densely packed with ribsomes except in the collar where their density decreases along its length, the distal end lacking them completely. A large contractile vacuole, which always appears collapsed in fixed material, occurs in the posterior end of the cell. Irregularly shaped vacuoles with coated vesicles attached to their membrane have also been seen in this position and probably represent an early stage in contractile vacuole growth. The remainder of the cell is occupied by spherical vasicles which from their size (approximately 2.0 um) and contents appear to be producing the spherules. Some have very dense contents and the membrane of such vesicles can sometimes be seen to invaginate and possibly abstricts small vesicles into the interior. Vesicles in which this invagination occurs are also surrounded by pyriform vesicles with very dense contents and microtubules can also be seen in the surrounding cytoplasm. None of the larger vacuoles could be identified as food vacuoles and phagotrophy was never seen in the living cells. The manner in which the spherules are released was not determined but at the level of the nucleus they often indent the cell outline and this may indicate the recent fusion of a spherule-containing vesicle with the cell membrane. The flagellar apparatus is complex and unusual in the relative arrangement of its various components. Although it was impossible to obtain clean shadow-cast preparations, it was seen that the flagellum appeared completely smooth and of the same diameter along its whole free length. Sections show that for most of its length the flagellum has the usual 9+2 pattern of microtubules in cross-section, with a nromal diameter of about 300 nm. At the level of the distal end of the collar, however, there is only a single central microtubule and the flagellum is somewhat thicker (about 350 nm). Towards the proximal end of the collar the doublets become widely spaced, dilating the flagellar membrane to an overall diameter of about 560 nm. Cross-sections at this level show that the doublets are attached to the flagellar membrane by densely staining material and fine filaments join them laterally and also extend radially from a dense granule at the centre of each doublet-microtubule. The flagellum narrows to an intermediate diameter of about 460 nm for a distance of 300 nm before entering the cell. Immediately distal to this region, where the flagellum is tapering, the centre of the axoneme is occupied by a tapering plug of amorphos material about 200 nm deep and 150 nm in diameter. Between the proximal end of the plug and the distal end of the flagellar basal body the material linking the peripheral doublets with the flagellar membrane is particularly dense, and extends under the cell membrane as a continuous band for a short distance at the level at which the flagellum emerges from the cell. Internally, the doublet microtubules in the transition region are linked via dense radial spokes to a delicate structure which appears discontinuous in vertical section, the transitional cylinder. The doublets becomes the triplet microtubules of the basal body slightly below the point of entry into the cell and the distal end of the basal body is linked to the cell membrane by transitional filaments. The triplets are joined laterally by fine filaments. The flagellar basal body appears to be only about 350 nm long. The basal body is surrounded by the three concentric structures. The outer two (X and Y) appear to be identical and, as far as can be seen from the almost exactly transverse series of sections passing through tnem, they are complete rings. Each ring consists of a pair of parallel lines 20 nm part and 60 nm deep. The rings themselves lie about 20 nm apart and the proximal end of the outer lies approximately level with the distal end of the outer lines approximately level with the distal end of the inner. These two rings are linked at their closest point by evenly spaced radial teeth which are only clearly visible in transverse section. The innermost ring (Z) is more amorphous in structure. It appears as a diffuse but layered band about 80 nm wide in transverse section but can only just be detected in longitudinal section. The outer two rings appear to function as an organizing centre for the approximately 60 microtubules which originate close to them. Approximately one third descend relatively steeply into the cell body to a maximum measured distance of 5 um while the remainder run more shallowly, some immediately distal to the rhizoplast and Golgi body. Elongate vesicles have sometimes been seen to become aligned between this set of microtubules. The final component of the flagellar apparatus remaining to be described is a root which originates close to the flagellar base and passes obliquely into the cell body close to the "forming" face of the Golgi body. This descending root is circular in cross section and 260 nm thick with a dense core 110 nm in diameter. It is not cross-banded but does show some discontinuity in longitudinal section. (ref. ID; 5731)
Examined materials
P. digitatum was obtained from collections taken in February 1981 from an acid pool, pH 5.5, temperature 4 degrees C, on Studland Heath, Dorset (National Grid Reference SZ 033857). (ref. ID; 5731)
Measurements
Cells about 17 um long. (ref. ID; 1618)