HYPHOCHYTRIALES 



Until 1884 the only Phycomycetes that had been described pos- 

 sessed posteriorly uniflagellate or either apically biflagellate or 

 laterally biflagellate zoospores (or both). That year two papers were 

 published (Zopf, 1884; Fisch, 1884a) which indicated the existence of 

 yet another type of swarmer, namely, one bearing a single anterior 

 flagellum. Since then there were occasional reports of fungi with an- 

 teriorly uniflagellate zoospores, but the number remained small. 



Confirmation of the anteriorly uniflagellate character of the zoospore 

 in Rhizidiomyces by Coker (1923) and in Hyphochytrium by Valkanov 

 (1929b) and Karling (1939b) made necessary the segregation of these 

 fungi of obscure relationships from the true chytrids (Sparrow, 1935b, 

 1942, 1943), with whom they were associated by older writers. On the 

 strength of the hypothesis that the zoospore represents the most primi- 

 tive condition, it is supposed that the members of the Hyphochytriales 

 arose from anteriorly uniflagellate monad ancestors and underwent an 

 apparently limited (so far as diversity of types is concerned) but none- 

 theless parallel evolution with the posteriorly uniflagellate chytrid- 

 iaceous series. There is, however, another possible explanation. It has 

 been suggested by E. A. Bessey (1942) that these forms may have arisen 

 from anteriorly biflagellate ancestors through the loss of one flagellum. 



Because of their small number, the anteriorly uniflagellate species 

 were grouped together as a family of uncertain affinities and placed 

 immediately after the chytrids in the first edition (1943) of the Aquatic 

 Phycomycetes. Later, but in that same year (1943), the group was raised 

 to ordinal rank by Karling who gave it the name Anisochytridiales. It 

 seems more appropriate here to make use of the long-existing family 

 name. 



Karling divided the order into three families: (1) Anisolpidiaceae,. 

 including holocarpic predominantly monocentric forms, comparable 

 (as a group) to the Olpidiaceae of the Chytridiales; (2) Rhizidiomyce- 

 taceae, containing two genera of eucarpic monocentric forms, compa- 

 rable to the Phlyctidiaceae; and (3) Hyphochytriaceae, composed of a 



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