72 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



have recently suggested a radical revision of the taxonomy of 

 these groups based on the kind of pseudopodia and the nature 

 of their movement. 



Superclass Rhi^opoda 



Amebo-flagellates, placed by Chatton (1953, in the Grasse 

 treatise) as the first suborder of amebae, are remarkable for their 

 double identity. Perfectly conventional small amebae, they are 

 capable of transforming for short or prolonged periods into 

 zooflagellates, reproduction occurring in either or both phases. 

 Brief electron-microscope observation of Tetramitus rostratus 

 (Pitelka and Schooley, 1955; Pitelka and Balamuth, unpublished) 

 demonstrated that in the flagellate phase only, the organism has 

 a pellicle reinforced with evenly spaced, parallel, fine fibrils, very 

 similar to the pellicle of some simple zooflagellates {e.g., Trypano- 

 soma, p. 137). Whether the whole body surface is so clothed is 

 not known. In fragmented cells, tracts of fibrils remain attached 

 to kinetosomes of the four anterior flagella, suggesting a physical 

 linkage. 



A single electron micrograph published by Cigada and Cantone 

 (1960) depicts a small monoflagellate cell believed to be a gamete 

 of Amoeba spumosa. Unfortunately, not enough morphologic 

 detail is included to permit comparison with other flagellates. 

 Flagellate stages of rhizopods otherwise have not been examined. 



The common, naked, lobose amebae have been for many years 

 such attractive subjects for experimental studies in cell biology 

 that it is not surprising to find a fairly impressive number of 

 electron-microscope investigations devoted to them. By far the 

 most popular forms have been the giants, Amoeba proteus and 

 species of Pe/omyxa* Quite recently, several experimentalists and 



* Since the publication in 1926 by Schaeffer of a taxonomic study equating 

 the multinucleate Pe/omyxa carolinensis Wilson with Chaos chaos Linnaeus, 

 many biologists have adopted this usage. Chatton and Grasse (in Chatton, 

 1953) retain the genus Pe/omyxa but follow Schaeffer in synonymizing Amoeba 

 proteus Pallas with Chaos diffluens M tiller. Other experts, among them Kudo 

 (1959), conclude that Chaos chaos is unidentifiable from the early descriptions 

 and that both Amoeba and Pe/omyxa therefore are valid genera. The nomen- 

 clatural problem is even more chaotic than indicated here, and it seems 

 expedient to follow Kudo in using the more prosaic names. 



