Lentomonas
Lentomonas Farmer & Triemer, 1994 (ref. ID; 7304 original paper)
Euglenid
[ref. ID; 7304]
Diagnosis; Colorless euglenid found moving slowly among substrate and/or detritus with a creeping motion. Cells are heterodynamically biflagellate with both flagella possessing paraxial rods and merging from a subapical opening. The transition region of each flagellum is constricted slightly and is occluded by a dense matrix. The thinner flagellum is directed anteriorly and beats with a fiarly regular movement. The somewhat thicker and longer posterior flagellum contrasts irregularly, is directed posteriorly, and lies adjacent to the cell's ventral surface. Cells possess a feeding apparatus composed of two supporting rods an four vans that extend for nearly the entire length of the cell. The supporting rods are reinforced by a few central microtubules and a partially encircling in of microtubules. The four vanes are of approximately equal length, are centrally positioned between the supporting rods, and form a folded, loricate arrangement at their posterior end. Cells are rigid with a pellicle composed of longitudinally arranged ridges, each of which is slightly bifurcate ont is outermost edge, each of which is slightly bifurcate on the outermost edge. (ref. ID; 7304)
- Lentomonas applanatum (Preisig, 1979) Farmer & Triemer, 1994 (ref. ID; 7304 redescribed paper) reported author and year? (ref. ID; 4872)
See; Ploeotia applanatum (ref. ID; 4872)
Syn; Entosiphon applanatum Preisig, 1979 (ref. ID; 7304)
Lentomonas applanatum (Preisig, 1979) Farmer & Triemer, 1994 (ref. ID; 7304 redescribed paper) reported author and year? (ref. ID; 4872)
See
Ploeotia applanatum (ref. ID; 4872)
Synonym
Entosiphon applanatum Preisig, 1979 (ref. ID; 7304)
Diagnosis
Cells rigid, and obviously ventrally flattened, body shape oval, 13.5-19.5 um long, 10-14 um wide, and 6-8 um thick, posterior frequently being slightly rimmed. Also in the anterior with slight rim at the spot where the vestibulum opens. Pellicle with 10 longitudinal ridges separated by many wide and rounded furrows. Seven to eight ribs are located on the obviously convex dorsal side, with 2-3 small ribs on the flat to slightly convex of concave ventral side. The anterior flagellum is usually somewhat shorter than the body, while the posterior flagellum is 1.5-2.0 times the body length. Cytoplasm colorless, never rich in grains. The nucleus is indistint and lies slightly left of the cell's center. (ref. ID; 7304)
Descriptions
Cells of L. applanatum are rigid, ventrally flattened, and oval when viewed from the dorsal side. The pellicle is composed of 10 longitudinally arranged ridges (seven on the dorsal side, three on the ventral surface), two of which form a channel on the ventral surface in which the posterior flagellum lies. The anterior flagellum is slightly less than body length and beats with an undulating motion while the thicker posterior flagellum trails underneath the cell's ventral side and is one and a half to two times body length. A large nucleus with permanently condensed chromosomes and a single nucleolus lies to the cell's left (when viewed dorsally) in a median to anterior position. Numerous mitochondria with plate-like cristae are present throughout the cytoplasm as are several Golgi apparatuses, including one that apparently produces the feeding apparatus vesicles. Trichocysts were seen near the periphery of the cell and are docked beneath the crests of pellicular ridges. Food vacuoles were primarily found in the posterior portion of the cell. Paramylon grains were not observed. (ref. ID; 7304)
- Feeding apparatus: The feeding apparatus of L. applanatum is composed of two supporting rods and four associated central vanes. Originating in the most posterior portion of the cell, the feeding apparatus extends the entire length of the cell and lies adjacent to the ventral surface. At its distal end, the feeding apparatus appears as a single row of microtubules adjacent to the pellicle. Anterior to this region, a number of microtubules are added to the original row. These microtubules are arranged into a W-shaped configuration and have four vanes closely appressed to them. The central vanes extend the length of the feeding apparatus; each terminates on a single microtubule. An electron dense material is associated with the outermost microtubules. Eventually this material becomes organized into the two supporting rods of the feeding apparatus and a small group of microtubules becomes associated with the central portion of each rod. One supporting rod has 10 to 12 central microtubules arranged in a single row while the other rod has its central microtubules arranged in a matrix. The micronucleus, which are continuous at the posterior end of the feeding apparatus, separate anteriorly and eventually line the inner sides of the supporting rods.
As they proceed anteriorly, the four vanes change from their folded or "plicate" arrangement and more away from the supporting rods into a more central position. A secondary thickening, associated with each vane, is visible mid-way along the feeding apparatus and becomes more prominent toward the anterior end as the vanes themselves become smaller. At the posterior end of the feeding apparatus, the two supporting rods are united by an electron-dense bridge and the microtubules associated with the outer and central portions of the supporting rods terminate.
Several other structures are also present in the anterior portion of the feeding apparatus. One of these, the anterior cap, is composed of electron-dense material embedded in the cytoplasm. A large bundle of microtubules arises from the anterior cap and forms a ring that partially encircles the feeding apparatus. This ring of microtubules extends to the side of the flagellar opening away from the feeding apparatus, where it appears as a microtubular comb. The actual cytostome is surrounded by the central vanes and their thickenings. A large number of vesicles are associated with the anterior portion of the feeding apparatus.
In addition of the microtubules of the supporting rods and comb, there is a small group of microtubules that extends from the flagellar opening toward the cytostome. No pocket or cavity was found associated with these microtubules. Examination of living cells suggests that the feeding apparatus of L. applanatum does not protrude from the cell. (ref. ID; 7304)
- Pellicle: The pellicle of L. applanatum is composed of 10 prominent ridges that extend longitudinally along the axis of the cell. Cells are rigid and were never observed to undergo metaboly. The outermost edge of each pellicular ridge is unevenly bifurcate. Microtubules underlie the crest of each pellicular ridge but were not observed in the region between pellicular ridges. All the pellicular ridges are united at the cell's posterior end and form a slight depression at the point of their union. At the anterior end of the cell, the pellicular ridges curve over and extend down the ventral surface. The ridges become smaller as they proceed along the ventral groove until eventually their microtubules become associated with those of the flagellar opening. (ref. ID; 7304)
- Flagellar apparatus: The two flagella of L. applanatum emerge from an opening on the ventral surface of the cell. The thicker of the two flagella is directed posteriorly, adjacent to the cell's ventral surface, and is designated as the posterior flagellum while the thinner anterior flagellum is directed anteriorly. Both flagella have paraxial rods, with the paraxial rod of the posterior flagellum being more prominent and having an electron-dense structure associated with it. Sudden contractions of the posterior flagellm result in a change of direction for the cell, but usually the posterior flagellum is passively dragged along the substrate. In contrast the anterior flagellum actively beats along its entire length.
The flagellar apparatus of L. applanatum consists of two functional basal bodies, microtubular roots, and several connective fibers. The transition zone between the axoneme and basal body is characterized by an electron-dense constriction. Beneath this region, a central structure extends the length of the basal body and gives it a nine-plus-one pattern.
The basal bodies occupy a ribosome-free zone at the base of the reservoir. A striated connective fiber extends between the two basal bodies and attaches to some of the triplets of each basal body. When seen in longitudinal section, the connective fiber did not appear as an extensive sheath that ran the length of the basal bodies but rather as a relatively fine fiber connecting the basal bodies. In addition to the striated connective fiber, a thin fiber connects the posterior basal body to the pellicle. A similar fiber connecting the anterior basal body to the pellicle was not observed.
Whereas several distinct groups of microtubules can be seen surrounding the flagellar reservoir, only the intermediate root can be clearly observed in the basal body region of the cell. The seven-member intermediate root originates adjacent to the posterior basal body and proceeds anteriorly between the two basal bodies. Serial sectioning did not reveal additional basal bodies in interphase cells. (ref. ID; 7304)
Remarks
The organism described in this paper was identified synonymously with E. applanatum Preisig (1979). Lentomonas applanatum has many of the characteristics found in Entosiphon species (e.g. prominent pellicular ridges, heterodynamic flagellation, well-developed feeding apparatus) and based solely on light microscopic observations the original assignment of L. applanatum to the genus Entosiphon was appropriate (Preisig 1979). What Preisig (1979) could not determine with light microscopy was that L. applanatum did not share many ultrastructure features with E. sulcatum and that a more appropriate taxon was required.
Of the many described species of Entosiphon (Huber-Pestalozzi 1955; Preisig 1979; Skvortzov 1957; Skvortzov et al. 1969), only the type species E. sulcatum has been examined with electron microscopy (Mignot 1966; Mignot & Hovasse 1973; Solomon et al. 1987; Triemer 1988; Triemer & Fritz 1987). While light microscopic observations show that L. applanatum bears a resemblance to E. sulcatum, a careful examination of the ultrastructural characters reveals that the two species differ significantly in terms of their flagellar apparatus, feeding apparatus, and pellicular structure. Based on these features it is clear that the two organisms do not belong to the same genus and that L. applanatum cannot be assigned to any existing euglenid genus. For this reason we have chosen to erect the new genus Lentomonas to describe the "leisurely manner" in which the cell moves. (ref. ID; 7304)