Filoreta tenera (Tekle et al, 2007)

 

Diagnosis: Filoreta with cell body and fine pseudopodial strands up to 10 µm and 1 µm wide, respectively. Mature cells delicate in appearance with short duration of anastomosing network. Spherical, smooth-walled, multinucleate cysts. Cytoplasmic condensation absent. Intermittent bidirectional movement of granules. Forms small round buds.

 

Ecology: The species was isolated from sediment collected from the edge of a man-made salt marsh near Beaufort, North Carolina, USA.

 

Remarks: This amoeba shares a number of morphological characters with the described members of Corallomyxa at the light microscopy level. These include:

 

  • the presence of multiple nuclei (plasmodium),
  • formation of anastomosing reticulate pseudopodia in the form of a network
  • production of buds under some conditions.

 

The following text is from Tekle et al (2007):

 

Filoreta (Corallomyxa) tenera forms irregular pseudopodial strands from which fine threads emerge. Individuals in older cultures often formed large, delicate and reticulate networks. Networks are comprised of elements of varying thickness, with the largest designated as cell bodies, and a meshwork of thin hyaline cytoplasmic extensions. After being disturbed, individual cells settle within approximately 5 min. and immediately begin to form networks. Preparations on glass slides observed after 3 h had expanding networks; the maximµm extent of a network was close to 300 µm across. The maximum width at any plasmodial segment was approximately 12 µm.
Cytoplasmic extensions that linked elements of the network were approximately 0.5 µm wide and enclosed a region as large as 89.0 µm-66.1 µm (average 34.8 µm-26.9 µm; n=8). Bidirectional streaming of the granules was only occasionally observed and occurred only over short spans of the network. The cell bodies contain most nuclei and can be distinguished only as a somewhat wider portion of the entire network with a granular appearance.
From observations on stained cells nuclei are mostly clustered in these wider granular portions, cell bodies, of the network. The diameters of nuclei in stained preparations ranged from 1.6 to 4.3 µm (avg. 2.4 µm; n=17).
The organism readily encysts. Cysts were smooth walled and rounded with diameters ranging from 7.7 to 17.8 µm. Cultures grown on bacteria may eventually consist entirely of cysts. Older cysts show shrinkage of the cytoplasm away from the cyst wall.
The general appearance of the isolate is the same regardless of food source. However, after approximately 4 days on the eukaryotic food source relatively large irregularly shaped amoebae appear in the culture with the coincidental disappearance of the plasmodial network. These amoeboid forms did not have tapering pseudopods. From these forms, numerous small rounded structures could be observed and we refer to these as buds. These appeared at seemingly random points within the network. Observation of the entire budding process was incomplete. Once separated from the parent cell, the presumed buds were not observed to float of their own accord, but were found close to the substrate. These amoeboid forms were not seen when Filoreta tenera was grown exclusively on bacteria. Cysts were also present in this culture after 4 days. The condensation described for C. multipara and C. nipponica was not observed under our culture conditions, regardless of the food source.