CHAPTER 3 



RHIZOPODS, ACTINOPODS, 

 SLIME MOLDS, SPOROZOA 



A proper phylogenetic approach to a discussion of protozoan 

 morphology would require that we consider first the flagellates, 

 but for the purpose of this review we shall abandon phylogenetic 

 propriety and begin with the amebae. Although they are not 

 primitive, their specializations are not primarily morphological — 

 at least not at the level yet visualized by electron microscopy. 

 They have for the most part discarded in the adult cell that 

 remarkable organelle, the flagellum, and their most conspicuous 

 common characteristic is the absence of an architecturally elaborate 

 cortex and pellicle. Hence they may serve us, as they have served 

 generations of text-book writers, as a convenient introduction 

 to the cell types we will consider. Indeed, many of their charac- 

 teristics have already been described as examples of protoplasmic 

 structures in the preceding chapter. 



The rhizopods, including the naked and testate amebae and the 

 foraminifers, are placed by Grasse (whose taxonomic scheme, as 

 presented in his Traite de Zoologie, 1952-53, is followed here) in 

 a Subphylum Rhizonagellata with the flagellates, from which they 

 probably originated polyphyletically. Amebo-flagellates, showing 

 characteristics of both groups, unfortunately have not been 

 examined in detail by electron microscopists. The radiolarians, 

 acantharians, and heliozoans are given separate status by Grasse 

 as a Subphylum Actinopoda ; many of them also have flagellated 

 gametes. Actinopods have in common the possession of very 

 slender pseudopodia, called axopodia, radiating from a generally 

 spherical body. These differ conspicuously from the lobose 

 pseudopodia of many amebae, but in some respects resemble the 

 reticular fine pseudopodia of the Foraminifera or the fllopodia 

 of some other ameboid organisms. Jahn, Bovee, and Small (1960) 



71 



