Sporozoa 319 



Taxonomy 



The taxonomy of the order has been discussed by Granata (39). Two 

 families have been recognized. The spores of the Tetractinomyxidae have 

 a continuous endocyst and an outer membrane composed of three valves. 

 The endocyst is lacking in the Triactinomyxidae. 



Fig. 6. 30. Spores of Actinomyxida: A. Sphaeractinomyxon gigas Granata, 

 lateral view, x850 (after G.); compare with Fig. 6. 26, E. B, C. Neoactino- 

 myxum globosum Granata, from stained (B) and living (C) material; x2470 

 (after G.). D. Triactinoinyxon legeri Mackinnon and Adam, two horns ex- 

 panded and the third partly expanded; sporoplasmic mass lies near the 

 upper pole; x260 approx. (after M. & A.). 



The following genera have been included in the two families: 



Family 1. Tetractinomyxidae: Tetractinomyxon Ikeda (58). 



Family 2. Triactinomyxidae: Guyenotia Naville (94), Hexactinomyxon Stole (39), 

 Neoactinomyxon Granata (39; Fig. 6. 30, B, C), Sphaeractinomyxon Caullery and 

 Mesnil (39; Fig. 6. 30, A), Synactinomyxon Stole (39), and Triactinomyxon Stole (39, 

 84). 



Order 3. Microsporida. These are small and generally intracellular 

 parasites, mostly of arthropods and fishes, although a few have been 

 reported from annelids and other hosts. As parasites of insects, Micro- 

 sporida are commonly found in the epithelium of the gut and in the 

 fat body or other tissues. Species invading fishes are commonly found in 

 the skin and muscles. 



The characteristic spores (Fig. 6. 31), the smallest of which may resem- 

 ble yeasts or large bacteria, range from about 2.0 to more than 20[jl in 

 length in different species. It is doubtful that the spore membrane is 

 composed of separate valves. A single polar filament is the rule, although 

 two are present in Telomyxa. The polar filament, when extended, is 



