CHYTRIDIALES 119 



goniosporum and Phlyctidium bumilleriae have been invaded by Rhi- 

 zophydium parasitans (Scherffel, 1925b) and Septosperma anomala 

 (Couch, 1932), respectively. Prosporangia of Polyphagias euglenae have 

 been known to be attacked by a species of Rozella (R. polyphagi 

 Sparrow, 1936a). The incidence of hyperparasitism among the chytrids 

 has been reviewed by Karling (1942a). He points out its relative rarity. 

 Since his first report was published, however, a number of additional 

 instances have been observed (Karling, 1944f; 1946a; 1946d; 1948b; 

 1949d; Sparrow, 1948; Willoughby, 1956). 



SYSTEMATIC ACCOUNT 



CHYTRIDIALES 



Microscopic parasitic or saprophytic primarily aquatic fungi of simple 

 body plan, the thallus either endobiotic, without specialized vegetative 

 structures and converted as a whole (holocarpic) into one or more 

 reproductive organs, or epi-, endo-, or interbiotic or extramatrical 

 and differentiated into a more or less extensive unbranched or branched, 

 generally nonseptate rhizoidal (rarely tubular and septate) vegetative 

 system at least the tips of which in interbiotic and extramatrical forms 

 are endobiotic, and one (monocentric) or more (polycentric) repro- 

 ductive organs (eucarpic); contents refractive with glistening globules 

 and minute granules, walls occasionally giving a cellulose reaction; 

 zoosporangia discharging after the deliquescence or rupturing of one 

 or more papillae (inoperculate) or after the dehiscence of an operculum 

 (operculate), zoospores generally formed within the sporangium, poste- 

 riorly uniflagellate (flagella lacking in several genera), usually bearing 

 a conspicuous oil globule, movement hopping or swimming or amoeboid, 

 encysting before penetration; resting spore thick-walled, generally 

 filling its container, often with a large globule, asexually formed or 

 sexually after fusion of isogamous planogametes or anisogamous aplan- 

 ogametes borne in thalloid gametangia, upon germination functioning 

 as a zoosporangium or prosporangium. 



Occurring on a wide variety of fresh-water algae; also on fresh- 

 water fungi, pollen grains, decaying plant tissues, and microscopic 



