FINE-STRUCTURE OF AN UNUSUAL RHIZOPOD, PENARDIA-COMETA, CONTAINING EXTRUSOMES AND KINETOSOMES

A study of the fine structure of a small freshwater amoeba Penardia co meta with branching filiform pseudopodia is performed. Cells are surro unded only by the plasma membrane with poorly developed glycocalyx. Th e centre of the cell is occupied by a large nucleus with a central nuc leolus. Adjacent to the nucleus lies a solitary dictyosome of the Golg i apparatus. Spherical mitochondria contain lamellar cristae. A pair o f parallel, normally developed kinetosomes is found near the dictyosom e. A mushroom-like protrusion of the plasma membrane without any inter nal substructures corresponds to each kinetosome. No microtubular nor fibrillar rootlets are observed. A bundle of several microtubules rang es along each pseudopodium; they continue inside the cell body. A lot of very complex extrusomes - microtoxicysts - lie in the cortical cyto plasm of the cell and adjacent to the membrane of pseudopodia. The tax onomic status of Penardia is uncertain. Its structure in question is c ompared with that of the filose and granuloreticulose amoebae and cent rohelid heliozoa.