SAP RO LEG N I ALES 803 



containing structure, contents with globules, germination not observed, 

 antheridial cell present or absent. 



Endobiotic holocarpic saprolegniaceous parasites of fresh-water and 

 marine diatoms, of marine Phaeophyceae and Rhodophyceae, and of 

 Phycomycetes. 



KEY TO THE GENERA OF THE ECTROGELLACEAE 



Sporangium unbranched 



Zoospores generally encysting outside the sporangium ; cysts spher- 

 ical; parasitic in diatoms and Phycomycetes 

 Parasitic in diatoms; antheridial cell, where known, not forming a 



fertilization tube Ectrogella, p. 803 



Parasitic in Phycomycetes; antheridial cell forming a well-defined 



fertilization tube Pythiella, p. 812 



Zoospores encysting within the sporangium or outside ; cysts angular ; 

 parasitic in marine Phaeophyceae and Rhodophyceae 

 Sporangium becoming partly extramatrical at maturity, with one 

 or two broad discharge tubes; zoospores encysting within the 

 sporangium ("net-sporangium'\) or emerging at once 



EURYCHASMA, p. 814 



Sporangium remaining completely endobiotic at maturity, with 

 numerous narrow discharge tubes; zoospores encysting 



outside Eurychasmidium, p. 820 



Sporangium branched Aphanomycopsis, p. 824 



ECTROGELLA Zopf 



Nova Acta Acad. Leop.-Carol., 47: 175. 1884. Emend. Scherffel, Arch. 



Protistenk., 52:5. 1925 



(Fig. 60 A-C, G-J, p. 806) 



Thallus endobiotic, tending to force apart the valves of the host and 

 to become partly extramatrical, holocarpic, without a specialized 

 vegetative system, tubular or occasionally rounded, unbranched, con- 

 tents at first vacuolate, later coarsely granular; sporangium bearing 

 from one to many short conical discharge tubes; zoospores formed in 

 the sporangium, diplanetic, primary spores biflagellate or nonflagellate, 

 swimming directly away or encysting at the orifice, secondary spores, 

 where known, biflagellate; resting spore endobiotic, thick-walled, com- 

 pletely tilling or lying loosely in a saclike containing structure, accom- 



