460 AQUATIC PHYCOMYCETES 



CLADOCHYTRIACEAE 



Thallus intra- or extramatrical, or both, eucarpic, usually strongly 

 polycentric, the vegetative system extensive, much branched, tubular, 

 rhizoidal, septate or nonseptate, often with irregular swellings and 

 septate turbinate cells; sporangia inoperculate, terminal or intercalary, 

 zoospores posteriorly uniflagellate (the flagellum apparently lacking in 

 one genus), with a single globule; resting spores thick-walled, apparently 

 asexually formed, borne like the sporangia on the rhizoidal system, upon 

 germination functioning as a prosporangium or zoosporangium. 



Primarily saprophytic in decaying vegetable debris and parasitic in 

 the eggs of microscopic animals and in fresh-water algae. One genus 

 parasitic in marine algae. 



"Endoopercula" have been found in some forms. 



Because of the remarkable alternation of an epibiotic monocentric 

 phase with an independent endobiotic strongly polycentric one, the 

 genus Physoderma, formerly included here, is maintained distinct from 

 the Cladochytriaceae, and is placed in a family of its own — the Physo- 

 dermataceae (see p. 482). 



KEY TO THE GENERA OF THE CLADOCHYTRIACEAE 



Vegetative system predominantly rhizoidal and nonseptate except for 

 the turbinate cells 

 Zoospores flagellate, sporangia internally proliferous 



Sporangia and rhizoids predominantly endobiotic, the sporangia 

 terminal or intercalary, often apophysate, with a discharge 

 tube; zoospores at discharge forming a temporary motionless 



group Cladochytrium, p. 461 



Sporangia and rhizoids predominantly extramatrical, sporangia 

 without a discharge tube, borne at the tips of the rhizoids; 

 zoospores at discharge swarming for a time in a vesicle at the 



orifice Physocladia, p. 475 



Zoospores nonflagellate, strongly amoeboid, sporangia not prolif- 

 erating Amoebochytrium, p. 476 



Vegetative system predominantly tubular, septate or nonseptate 

 Vegetative system intra- and extramatrical, mycelioid, with one or 

 more axes, nonseptate or occasionally septate; sporangia of two 

 types, smooth and tuberculate Polychytrium, p. 477 



