Vampyrella lateritia (Fresenius, 1856) Leidy, 1879
Diagnosis: Cells compact, often spherical, sometimes broader than long with respect to the direction of movement; size quite variable, young trophozoites about 25-40 µm, larger trophozoites (maybe derived from cell fusions) about 70 µm. Cell body with radiating pseudopodia, occasionally accumulating at the frontal edge during movement.
Intense orange coloration of the central cell body, periphery and pseudopodia colorless. Cells float freely in the water column, or perform stalking, paddling movements. Pseudopodia long and thin, tapering, mostly unbranched; hyaloplasmatic; more or less equally distributed over the cell, sometimes in tufts. Numerous, highly refractive granules, about 0.5-1.5 mm in size (membranosomes) moving along the pseudopodia, occasionally shooting rapidly out of the cell cortex connected by a thin cytoplasmic strand and subsequently retracted; the latter phenomenon results in the so-called ‘pin-like’ or ‘pinhead’ pseudopodia. Rarely formation of broad, claviform pseudopodia occurs; possibly related to pathological conditions. Occasionally numerous vacuoles present, predominantly in the peripheral cytoplasm, not always conspicuous at lower magnifications.
Cells can fuse to large, deformed plasmodia showing the same structure and color as the trophozoites; predominantly occurring in old cultures under food limitation.
Digestive cysts with a roundish cyst outline: roundish, elliptical, often slightly flattened towards the substrate when seen from the side; smallest roundish cysts about 35 µm in diameter, cysts more often slightly elliptical or oviform and ranging in size from 50-100 µm. Cysts with two cyst envelopes: outer envelope delicate, with even or slightly irregular surface, sometimes spiny outline; seems to resemble the cell outline before cyst formation and is likely formed at this stage. The inner cyst envelope is stronger than the outer, invariably with even surface; covering the cell body tightly until cell divisions commence. Young cyst stages greenish with roughly granulated content; during digestion turning orange-red; mature cysts with distinct food remnants as several brown conglomerates of various sizes. After internal cell division daughter cells (usually four) often visible in a typical tripartite arrangement; during hatching the food remnants are exocytosed and left behind in the empty cyst envelope.
Resting cysts with seemingly four envelopes surrounding deep orange granular cyst content: the outermost envelope resembles the delicate, outer envelope of digestive cysts; with irregular, spiny outline. The next inner envelope is also very delicate, sometimes hardly visible; seems to be connected to the second innermost envelope by radial strand-like structures. The second innermost envelope is comparatively prominent, with even surface; maybe corresponding to the inner envelope of digestive cysts. The innermost envelope shows a warty surface; containing the spore content; diameter about 25 µm. Resting cysts only once observed.
Feeding behavior. Trophozoites attach to an algal cell, often accompanied by retraction of the long pseudopodia as well as flattening of the cell body increasing the contact area. After several minutes the algal cell wall bursts locally and most of the extruded protoplast is quickly injected into a large food vacuole of the trophozoite (likely due to the turgor pressure). The remains of the disintegrated protoplast within the algal cell are engulfed by means of an ingestion pseudopodium. Several algal cells can be devoured in this way until the green amoeba enters the immobile digestive phase.
Proven food organisms. Zygnema spp., Spirogyra spp.
This genus contains amoeboid organisms which feed on algae.