802 AQUATIC PHYCOMYCETES 



affinities with the Saprolegniaceae. In the Ectrogellaceae features such 

 as the sequence of changes in the maturing sporangium, the diplanetic 

 (dimorphic) character of the biflagellate zoospores, and the cellulose 

 wall are all saprolegniaceous. Although the affinities of Thraustochyt- 

 rhan are as yet somewhat obscure, its methods of zoospore discharge, 

 the biflagellate zoospores, and internal proliferation of the zoospo- 

 rangium of T. proliferum all point to a relationship with the Sapro- 

 legniaceae. The newer members of the family, added in recent years, 

 further confirm this (Kobayasi and Ookubo, 1953). 



KEY TO THE FAMILIES OF THE SAPROLEGNIALES 



Thallus holocarpic, endobiotic during development, more or less extra- 

 matrical at maturity; zoospores mono- or diplanetic (mono- or 

 dimorphic), behaving variously after discharge; primarily para- 

 sites of fresh-water and marine diatoms and Phaeophyceae 



Ectrogellaceae, p. 802 

 Thallus eucarpic, intra- and extramatrical; saprophytic or parasitic on 

 a wide variety of substrata 

 Thallus resembling that of a monocentric chytrid, the reproductive 

 rudiment epibiotic, the vegetative system rhizoidal 



Thraustochytriaceae, p. 828 

 Thallus consisting of a more or less well developed complex of tubu- 

 lar hyphae without constrictions, the extramatrical parts of 

 which bear numerous reproductive organs . . Saprolegniaceae, p. 833 1 



ECTROGELLACEAE 



Thallus endobiotic, sometimes more or less extramatrical at maturity, 

 one-celled, unbranched or sparingly branched, holocarpic, walls turning 

 blue with chloriodide of zinc, contents at first vacuolate, later coarsely 

 granular; sporangium inoperculate with one or more discharge pores 

 which are sessile or at the tips of tubes; zoospores segmented within 

 the sporangium, diplanetic (dimorphic), primary zoospores biflagellate, 

 after discharge either undergoing a short period of motility before 

 encysting or encysting at once, secondary zoospores laterally biflagellate; 

 resting spore thick-walled, filling or lying loosely in a thin-walled 



1 See note. p. 792. See also Vishniac, in Mycologia, 50:66, 1958, where a new 

 family of holocarpic marine fungi, the RaMphthora.ceae(Haliphthorosmilfordensis), 

 is established, 



