world of amoeboid organisms

Chlamydomyxa labyrinthuloides  Archer, 1875

Chlamydomyxa labyrinthuloides is a heterokont alga known since the last century. It lives on Sphagnum and other water plants as aplanospores or plasmodia. Chlamydomyxa labyrinthuloides shares morphological features with xanthophytes and chrysophytes, whereas pigment composition indicates a grouping with the phaeophytes, raphidophytes and chrysophytes. The sequence of the SSU rRNA gene and its phylogenetic reconstruction unambiguously demonstrate that Chlamydomyxa labyrinthuloides is related to the chrysophytes.

Specimen from a glacial stream, El Chalten, Argentina
The same Specimen as above, detail in Phase Contrast
Specimen from a glacial stream, El Chalten, Argentina

In 1875 Archer described Chlamydomyxa labyrinthuloides as a new species and genus. He observed the germination of the aplanospore resulting in an amoeboid organism with finely branched filopodia and yellowish-green plastids in the central cytoplasm, but did not detect nuclei.

Aplanospores of Chlamydomyxa are rarely found within the hyaline cells of Sphagnum, but mostly between the moss `leaves’ and other water plants. In culture germination of the amoebae can be induced by changing the medium or by `washing’ the aplanospores with a Pasteur pipette. The germination rate can be rather low, only 5-10% after 3 days, and starts with partial disintegration of the cell wall. Finally, the cell hatches out through a more or less circular opening, leaving behind the remains of enclosed algae and reddish granules, which usually accumulates in older aplanospores. In many cases, cells leave the aplanospores without filopodia. The plasmodium either divides and the new one forms an aplanospore or it generates an aplanospore without division. In some cases cell division finishes before the whole plasmodium hatches out of the cell wall and the new aplanospore develops within the old cell wall. In other cases, the amoeba has thin multiple branches formed by the peripheral hyaline part of the cytoplasm even before the entire cell leaves the aplanospore.

In plasmodia (multinucleate amoebae) no dominant contractile vacuole is found. Instead many small vacuoles are present together with many granules. The disc-shaped chloroplasts are located in the central portion of the cytoplasm, and are yellowish-brown under high-light and greenish-brown under low-light conditions. Size of the plasmodia varies from 15 µm to 180 µm. Division of plasmodia is initiated by a constriction of the cytoplasm, giving a dumbbell-like impression.
Finally the cytoplasmic connection between the two parts brakes. Cell division is finished within 30 min. Repeated division or separation of small parts of the plasmodium can result in fragments that usually still contains several nuclei. Plasmodia move rather slowly, mostly by a distance of their own diameter or less during 1 h.

Chlamydomyxa phagocytoses diatoms (Eunotia, Frustulia, Pinnularia) and Synechococcus, but not bigger desmids. To induce phagocytosis, plasmodia must be cultivated for several days in darkness. Prey organisms (encountered by chance) are surrounded by filopodia and transported to the central part of the plasmodium in a large vesicle, where they were digested within 2-4 h.

Approximately 1 week after germination the plasmodium encysts. Aplanospore formation is initiated by retraction of the filopodia and parts of the central cytoplasm. After 1 day a cell wall is visible and after 1 week the wall often appears multilayered. In some cases it can be seen that the cytoplasm has retracted slightly and a new layer of the cell wall has developed. In older cultures deficient in nitrogen and phosphorus, a red pigment accumulates in the aplanospores. To eliminate these pigmented granules, a part of the organism hatches out of the cell wall, the granules are ejected, and the cytoplasm retracts back and develops a new cell wall within the original cyst. Chlamydomyxa sometimes encysts inside the original aplanospore without developing new plasmodia, or division of the cytoplasm can take place prior to this encystment.

Zoospores are not detectable. However, morphological features do not unambiguously place Chlamydomyxa within the chrysophytes. Amoeboid or plasmodioid structures as the main stage in the life history are seen in both the Chrysamoebae or Myxochryidae. The Chrysamoebae (Poche, 1913) are defined as naked cells with a tendency to form lobed and branched extensions. Vegetative cells are amoeboid in most parts of the life history ; flagellate states occur in some genera and in others were never observed. This difference was used to place those organisms with a flagellate state in the Rhizochrysidae Pascher ex Reichennau and those in which it is absent in the Chrysachniaceae Pascher (1931). Today the absence of flagellate states is not considered to be a good taxonomic feature (Preisig, 1995). Amoeboid states occur in different groups of chrysophytes.

The above information is from Tekle et al, 2007.

Ferry Siemensma, created March 2, 2019; last modified January 31, 2021
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