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Omnivora mutabilis
O. mutabilis

Omnivora mutabilis (Bailey, 1853) Dumack, Pundt and Bonkowski, 2019
Basionym: Pamphagus mutabilis Bailey, 1853
Synonym: Pseudodifflugia caudata Penard, 1910

Diagnosis: test a highly flexible, colorless, hyaline membrane, following the size changes of the cytoplasm during feeding or starvation; shape usually pyriform or droplet shaped, with the pseudostome on the broad base; filopodia usually few, long and strait, branching. Large filopodia slightly taper, smaller filopodia are rod shaped, with parallel sides. Longitudinal division.

Dimensions: 103-150 µm long; my measurements: 133-264 µm; nucleus c. 33 µm.

Ecology: In different types of water, on sediments and between waterplants; easily overlooked because of the resemblance with a piece of debris. I’ve also found it in eutrophic water. Food: mostly different kind of algae and diatoms.

Remarks: the pseudostome is hard to observe; it is usually a small slit and often hidden between folds of the membrane.
Originally this curious organism has been described as Pamphagus mutabilis. The use of the name Pamphagus is not correct according to the International Rules, as pointed out by Wailes (1915).
Several authors has described a species under this name, but only few has apparently seen what Bailey described as follows: “If the reader will imagine a bag made of some soft extensible material so thin as to be transparent like glass, so soft as to yield readily by extension when subjected to internal pressure, and so small as to be microscopic; this bag filled with particles of sand, shells of diatoms, portions of algae or desmids, and with fragments of variously colored cotton, woolen, and linen fibers, will give a picture of the animal; to complete which it is only necessary to add a few loose strings to the bag, to represent the variable radiant processes which it possesses around the mouth.”
Penard (1910) described this amoeboid as Pseudodifflugia caudata.

Omnivora mutabilis
O. mutabilis, compressed by the coverslip, showing the nucleus. It is the same specimen as the one above.
Omnivora mutabilis
O. mutabilis, 264 µm long
Pamphagus mutabilis
Pamphagus mutabilis
Pamphagus Lecythium mutabilis
Characteristic pear shaped specimens, with the pseudostome below.
Pamphagus Lecythium mutabilis
O. mutabilis, 239 µm long
Pamphagus mutabilis
O. mutabilis, 200 µm long – stacked image
Pamphagus mutabilis
Cells collected with a stereomicroscope and a micro pipette.
O. mutabilis, 214 µm long; the arrow points to the aperture
Omnivora mutabilis
Nucleus
Pamphagus mutabilis
O. mutabilis, 136 µm
Pamphagus mutabilis
O. mutabilis, 160 µm, with some filopodia. This is the same specimen as the one on the first micrograph, just one day later. The specimen was kept in a moist chamber.
Pamphagus mutabilis
Longitudinal division. After some time the two cells separated.
Pamphagus mutabilis
Longitudinal division. After some time the two species separated, but I couldn’t observe the beginning of the process.
Omnivora mutabilis
Longitudinal division, Laegieskamp, December 2019.
Pamphagus mutabilis
O. mutabilis, filopodia; seen from above
Pamphagus mutabilis
Two types of filopodia, large tapering ones (blue arrow) and smaller rod-shaped (yellow arrow)
Lecythium mutabilis
Laegieskamp
Lecythium mutabilis
Specimen with employed filopodial network. This species is very sensitive for light and starts immediately retracting its filopodia when it comes into the lightbeam of the microscope.
Lecythium mutabilis
O. mutabilis, 166 µm long – Lolo Pass, Montana USA
Pamphagus mutabilis
O. mutabilis – drawing Dr. A.A. de Groot, ca. 1940, unpublished – collection Ferry Siemensma
Lecythium mutabilis
O. mutabilis – Wellington, Florida
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