Chapter 28 

 Subclass 3 Cnidosporidia Doflein 



THE members of this subclass possess without exception resist- 

 ant spores which are of unique structure. Each spore possesses 

 1-4 polar filaments and one to many sporoplasms. The membrane 

 which envelops these structures may be a single-piece or bi- or tri- 

 valved. The polar filament is typically coiled within a polar capsule. 



In the order Myxosporidia and Actinomyxidia, there appear 

 several cells during the process of sporulation. These cells give rise 

 to one to many sporoplasms or generative cells, capsulogenous 

 cells, and spore membrane. This condition is not observed in other 

 groups of Protozoa and for this reason some writers recognize a close 

 affinity between these two orders and the Mesozoa. The method of 

 multiplication in the Cnidosporidia is schizogonic and sporogonic. 

 The schizogony is binary or multiple fission, budding, or plasmo- 

 tomy. The nuclear division varies from amitosis to mitosis. Isogam- 

 ous, anisogamous, and autogamous reproduction have been re- 

 ported in a number of species. In many forms, the zygote is the 

 sporont, in which one to many spores become differentiated. 



No secondary or intermediate host has been found for any of the 

 Cnidosporidia. They are exclusively parasites of the lower verte- 

 brates and invertebrates. Since cnidosporidian infections occur 

 frequently in epidemic forms among such economically important 

 animals as the silkworm, honey bees, and commercial fishes, these 

 organisms possess considerable practical significance. 



The cnidosporidia are divided into the following four orders: 



Spores comparatively large 



Shell bivalve; 1, 2, or 4 polar capsules Order 1 Myxosporidia 



Shell trivalve; 3 polar capsules Order 2 Actinomyxidia (p. 531) 



Spores comparatively small 



Shell one-piece; 1 (or 2) polar filament. .Order 3 Microsporidia (p. 535) 



Barrel-shaped; a thick filament coiled beneath the shell; 3 sporoplasms 



Order 4 Helicosporidia (p. 542) 



Order 1 Myxosporidia Btitschli 



The spore of a myxosporidian is of various shapes and dimen- 

 sions. It is covered by a bivalve chitinous spore membrane, the two 

 valves meeting in a sutural plane which is either twisted (in three 

 genera) or more or less straight. The membrane may possess various 

 markings or processes. The polar capsule, with its short coiled 



515 



