LIGHT- AND ELECTRON-MICROSCOPICAL STUDY OF PELOMYXA FLAVA SP. N. (ARCHAMOEBAE, PELOBIONTIDA)
A. O. Frolov,1, * L.V. Chystjakova,2 M. N. Malysheva 1
1 Zoological Institute RAS, St. Petersburg, and 2 Invertebrate Zoology Department of
St. Petersburg State University;
*e-mail: frolal@yandex.ru
Using light and electron microscopy, the morphology of a new species of pelobionts Pelomyxa flava was
studied. The coverings of P. flava are represented by plasma membrane bearing the thick layer of weakly structured
glycocalyx on its outer surface. Numerous flagella are often located on the tops of short conical pseudopodia.
Kinetosomes of flagella reach a length of 0.9 μm and are hollow with a pronounced central filament. Rootlet
system is represented by three groups of microtubules: the radial, basal and microtubules of lateral root. The
transition zone is short and does not exceed the level of cell surface; the axoneme is characterized by an unstable
set of microtubules. Trophic stages of P. flava life cycle are presented by binuclear cells; plasmotomy is performed
at the tetranuclear stage. Nuclei have a granular structure. Fibrillar nuclear bodies were revealed in karyoplasm.
The nuclei shell has a complex organization. On its surface, the outer membrane has a layer of electron-
dense material which contacts with short microtubules, located in a row at the surface of the nuclear envelope.
The bubbles and cisterns of endoplasmic reticulum, which are the derivatives of the nuclear envelope, are
located outward from the microtubules. The presence of structural and digestive vacuoles and grains of glycogen
was noticed in P. flava endoplasm. Three types of prokaryotic cytobionts were revealed. Large multi-membranous
organelles reaching 5 μm in diameter were described for the first time. We discuss morphology and biology
features of P. flava in comparison with the previously studied Pelomyxa species.
Key words: pelobionts, morphology, Pelomyxa flava sp. n., ultrastructure
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