BL A STOCLA D I A L ES 6 3 5 



KEY TO THE FAMILIES OF THE BLASTOCLADIALES 1 



Thallus unwalled, without rhizoids, parasitic in aquatic larvae of in- 

 sects (mosquitoes); resting spores numerous, thick-walled, outer 



wall variously ornamented Coelomomycetaceae, p. 635 



(Coelomomyces ) 

 Thallus walled, bearing rhizoids, not confined to insect larvae 

 Thallus tubular, catenulate, unbranched or branched, bearing rhi- 

 zoids along its length, with true or false septa delimiting repro- 

 ductive structures and sterile isthmuses .... Catenariaceae, p. 650 

 Thallus of varying degrees of complexity, typically having a basal 



cell with rhizoids at its proximal end Blastocladiaceae. p. 659 



COELOMOMYCETACEAE 



Obligate parasites within the body cavity of insects; mycelium naked, 

 without rhizoids; thick-walled, resistant sporangia only present, the 

 entire mycelium used up in their formation; sporangial and zoospore 

 structure much as in other Blastocladiales; sporangia dehiscing by the 

 cracking of the outer wall along a preformed groove, the inner wall and 

 the contents swelling and pushing outward through this crack ; spores 

 discharged by the gelatinization of the exposed surface of the inner wall. 2 



In erecting a new family to accommodate this group of highly special- 

 ized parasites, primarily of mosquito larvae, Couch (1945b) pointed 

 out that they are more closely related to the Blastocladiales than to the 

 Chytridiales, the order in which these organisms were placed by Keilin 

 (1921) and others. 



Similarity with blastocladiaceous fungi is to be found in the coarse, 

 well-developed, dichotomously branched mycelium, the character of the 

 resting spore wall and its preformed line of dehiscence, and the structure 

 of the zoospore and its discharge and manner of swimming. Couch 

 noted, furthermore, that the parasitic habit of these fungi has been 

 accompanied by striking structural changes in the vegetative thallus. 

 No hyphal walls can be demonstrated, nor are there specialized food- 

 absorbing structures such as rhizoids. Evidently the whole naked, branch- 

 ed thallus functions vegetatively. Where hyphal bodies are formed, 

 they too are unwalled, a condition analogous to that in at least 



1 See also the recently described genus Oedogoniomyces ( p. 694), possibly belonging 

 in the Eccrinales. 



2 Revised for this treatise bv J.N. Couch. 



