ORDER BLASTOCLADIALES 81 



resting spores usually free from the hyphal membrane. These resting 

 sporangia are smooth or minutely granular. In germination the outer 

 wall cracks open and a tube emerges through which the zoospores are 

 discharged. Rhizoids are produced at almost any point on the thallus, 

 from the isthmuses as well as the reproductive swellings. Sexual repro- 

 duction occurs by the union of equal, motile gametes. One genus only is 

 known, Catenaria, which was formerly placed in the family Clado- 

 chytriaceae of the order Chytridiales until Couch (1945a) demon- 

 strated that the mode of reproduction is typical of some forms of the 

 Blastocladiales. 



Of the two well-studied species of the genus, sexual reproduction is 

 unknown in C. anguillulae Sorokin. It produces both thin-walled and 

 resting zoosporangia which appear to produce exactly similar zoospores. 

 In C. allomycis Couch, the zoospores from the thin-walled zoosporangia 

 produce plants with either or both types of sporangia. Those from the 

 resting sporangia produce less active zoospores which encyst at or near 

 the mouth of the exit tube. After about two hours these cysts produce 

 four gametes, each, which escape through a short papilla and sooner or 

 later unite by pairs to form posteriorly biflagellate zygotes. These swim 

 for a time, the two flagella lying close together and being synchronous in 

 their motions. The zygotes eventually encyst and penetrate the host 

 tissue by means of a slender germ tube. Apparently, pairing of the gametes 

 is rare between those from any one cyst. This type of reproduction is 

 practically identical with that of Blastocladiella cystogena Couch and 

 Whiff en (1942) and comparable to that of Allomyces cystogenus Emerson 

 as interpreted by McCranie (1942). (Fig. 23A-G.) 



Family Coelomomycetaceae. Coelomomycetaceae are parasitic in 

 the larvae of insects, chiefly mosquitoes. Mycelium coenocytic, non- 

 septate, lacking rhizoids and without demonstrable cell walls, branched 

 and somewhat anastomosing. Terminal portions of the short branches 

 enlarge and break free and develop resting spores surrounded by the 

 plasma membrane of the mycelium. These spores possess a thick outer, 

 colored wall, usually pitted or striate, and a thinner inner wall. Dehiscence 

 by a longitudinal slit. Zoospores posteriorly uniflagellate with an, at most, 

 imperfectly formed nuclear cap. No thin-walled sporangia nor sexual stage 



Fig. 23. Blastocladiales. (A-G) Family Catenariaceae. (A-F) Catenaria allomycis 

 Couch. (A) Chain of zoosporangia within filament of Allomyces. (B) Zoosporangium 

 with zoospores about to escape. (C) Resting sporangia within host filament. (D) 

 Zoospores emerging from germinating resting sporangium and encysting. (E) Cysts at 

 mouth of exit tube of resting sporangium. (F) Biflagellate zygotes formed by union of 

 gametes emerging from the cysts. (G) Catenaria anguillulae Sorokin, fluke egg with four 

 resting sporangia and several emptied thin-walled zoosporangia. (H, I) Family Coelo- 

 momycetaceae. Coelomomyces lativittatus Couch and Dodge. (H) Germinating resting 

 sporangium. (I) Zoospores. (A-G, courtesy, Couch: Mycologia, 37(2):163-193. H-I, 

 courtesy, Couch and Dodge: J. Elisha Mitchell Sci. Soc, 63(l):69-79.) 



