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Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec.

Rhogostoma spec.

Diagnosis: cell spherical or slightly ovoid, with a semi-rigid colorless, hyaline membrane or pellicle; aperture a small cleft, hardly visible with a light microscope; plasma fills the test nearly completely; filopodia usually few, long and straight, branching, without granules; usually the filopodia taper, but sometimes a thin finger-like pseudopodium is formed. Usually two filopodia stretch in opposite directions, one being the leading one. Cytoplasm with one or more strong refracting bodies. Nucleus not observed. One to two small contractile vacuoles. Cell can be very mobile.

Dimensions: small species, Ø 8.5-12 µm.

Ecology: Freshwater; feeding on bacteria. This species was found in a cold water tap in a kitchen in Zeist, The Netherlands. A sample was sent to me by Sandra Redeker, researcher at Het Waterlaboratorium in Haarlem, The Netherlands.

Remarks: I have placed this species in the genus Rhogostoma because of its slit-like aperture. Because of its minute size morphological details are hard to detect light microscopically. I couldn’t see any nucleus, maybe it has a granular structure.

Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec. - Ferry Siemensma
Cell in front view (left hand) and lateral view. Arrow indicates the slit-like aperture.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec. - Ferry Siemensma
Two filopodia at both ends of the aperture. The cleft is visible between the arrows.
Rhogostoma spec. - Ferry Siemensma
Cell with clearly visible cleft.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec., usually two filopodia stretch in opposite directions

Rhogostoma spec. - Ferry Siemensma

Rhogostoma spec.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec., the same specimen. Note the birefringent bodies. The slit-like aperture is visible.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec., compressed by the pressure of the cover slip. A sphere of hyaloplasm (above) is pressed out of the cell. The pressed shell looks larger than it is.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec. - Ferry Siemensma
A peduncle stretches through the aperture. Photomicrograph (lefthand) and drawing of the same photomicrograph.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec., flattened and collapsed by the pressure of the cover slip.
Rhogostoma spec. - Ferry Siemensma
Rhogostoma spec.
Rhogostoma spec. - Ferry Siemensma
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