Protistology 4 (3) 227-244 (2006)
Structure and development of Pelomyxa gruberi sp. n. (Peloflagellatea, Pelobiontida)
Alexander O. Frolov 1, Andrew V. Goodkov 2,
Ludmila V. Chystjakova 3 and
1 Zoological Institute RAS, St. Petersburg, Russia
Summary
The general morphology, ultrastructure, and development of a new pelobiont protist,
Pelomyxa gruberi, have been described. The entire life cycle of this eukaryotic microbe
involves an alteration of uni- and multinucleate stages and is commonly completed
within a year. Reproduction occurs by plasmotomy of multinucleate amoebae: they
form division rosettes or divide unequally. Various surface parts of this slowly-moving
organism characteristically form finger-shaped hyaline protrusions. Besides, during
the directed monopodial movement, a broad zone of hyaline cytoplasm with slender
finger-shaped hyaline protrusions is formed at the anterior part of the cell. In
multinucleate stages up to 16 or even 32 nuclei of a vesicular type may be counted.
Individuals with the highest numbers of nuclei were reported from the southernmost
part of the investigated area: the North-West Russia. Each nucleus of all life cycle stages
is surrounded with microtubules. The structure of the flagellar apparatus differs in
individuals of different age. Small uninucleate forms have considerably fewer flagella
per cell than do larger or multinucleate amoebae but these may have aflagellated basal
bodies submerged into the cytoplasm. In young individuals, undulipodia, where
available, emerge from a characteristic flagellar pocket or tunnel. The basal bodies and
associated rootlet microtubular derivatives (one radial and one basal) are organized
similarly at all life cycle stages. There is a thin-walled cylinder in the flagellar transition
zone, and an electron-dense column above that zone. In the separate non-motile
undulipodia the arrangement of axoneme microtubules deviates from the typical 9+2
eukaryotic pattern. In the cytoplasm of P. gruberi two types of rod-shaped
endocytobionts are present: (1) large bacteria with a pronounced longitudinal cleft,
and (2) smaller methanogen-like bacteria.
Key words: systematics, life cycle, Pelobiontida, Pelomyxa gruberi sp. n., ultrastructure,
cytoskeleton
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