CNIDOSPORIDIA, MYXOSPORIDIA 459 



the gills is usually manifest by whitish pustules which can be fre- 

 quently detected with the unaided eye. When the wall of the ah- 

 mentary canal, mesentery, liver, and other organs are attacked, 

 one sees considerable changes in them. Heavy myxosporidian in- 

 fection of the gall bladder or urinary bladder of the host fish may 

 cause abnormal appearance and coloration or unusual enlarge- 

 ment of the organ, but under ordinary circumstances the infec- 

 tion is detected only by a microscopical examination of its con- 

 tents. Certain histological changes in the host fish have been 

 mentioned elsewhere (p. 26). 



Severe epidemic diseases of fishes are frequently found to be 

 due to myxosporidian infections. According to Davis, the 

 "wormy" halibut of the Pacific coast of North America is due to 

 the myxosporidian, Unicapsula muscularis (Fig. 213), which in- 

 vades the muscular tissue of the host fish. The "boil disease" of 

 the barbel, Barbus harhus and others, of European waters, is 

 caused by Myxoholus pfeifferi. Myxosoma cerebralis which attacks 

 the supporting tissues of salmonoid fish, is known to be responsi- 

 ble for the so-called "twist disease," which is often fatal, espe- 

 cially to young fishes and which occurs in an epidemic form. 



The Myxosporidia are divided into three suborders : 



Largest diameter of spore at right angles to sutural plane; with 1 polar 

 capsule on each side; sporoplasm without iodinophilous vacuole 

 Suborder 1 Eurysporea 



Spore spherical or subspherical with 1, 2, or 4 polar capsules; sporo- 

 plasm without iodinophilous vacuole. . . . 

 Suborder 2 Sphaerosporea (p. 461) 



Sutural plane coincides with, or is at an acute angle to, largest diameter 

 of spore; 1, 2, or 4 polar capsules; sporoplasm with or without 

 iodinophilous vacuole Suborder 3 Platysporea (p. 404) 



Suborder 1 Eurysporea Kudo 



Spores laterally expanded; coelozoic in marine fish, except one species 

 Family 1 Ceratomyxidae 



Spores less laterally expanded; in freshwater fish; holozoic or coelozoic 

 Family 2 Wardiidae (p. 461) 



Family 1 Ceratomyxidae Doflein 



Spores are laterally prolonged and therefore sutural diameter is 

 smaller than width; 2 polar capsules at anterior margin; one on 

 each side of sutural plane. 



Genus Ceratomyxa Thelohan. Shell-valves conical and hollow, 



