Protistology 1 (3) 101–109 (2000)
Ultrastructure of the aloricate bicosoecid Pseudobodo tremulans, with revision of the order Bicosoecida
Serguei A. Karpov
Department of Invertebrate Zoology, Faculty of Biology and Soil Science, St. Petersburg State University, Russia
Summary
The fine structure of the colourless aloricate bicosoecid Pseudobodo tremulans has been studied in detail. There are two life
history stages expressed in cultures of this species, a sedentary trophozoite and a swarmer, which are slightly different in external
morphology. The anterior flagellum bears two rows of tripartite tubular mastigonemes, and the posterior one is smooth. The cell has no
other distinguishable surface decoration. The internal structure reveals typical features of bicosoecids. The largest rootlet of
P. tremulans (r3) is a broad microtubular band passing from the anterior basal body towards the cytostome region, which is
presented by a lip. At its proximal end, rootlet r3 has a characteristic L-shape in cross section and is normally associated with fibrillar
material. The posterior basal body is oriented to the left. A mitochondrion with tubular cristae is associated with the middle part of rootlet r3.
Small numbers of extrusomes is present. No microbody has been found. There is a structure similar to concentric rings in the transition
zone of each flagellum. The taxonomy of bicosoecids (including pseudodendromonads) is discussed, and a revision of the order is
proposed. The four included families are classified on the basis of characters associated with the cell surface and the feeding apparatus.
Key words: Pseudobodo tremulans, heterotrophic flagellates, ultrastructure, bicosoecids, pseudodendromonads
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