246 AQUATIC PHYCOMYCETES 



Rhizophydium megarrhizum Sparrow 



Aquatic Phycomycetes, p. 171, fig. lie. 1943 



Chytridium subangulosum, sensu Dangeard, Bull. Soc. Linn. Normandie, 



III, 9: 88. 1884-85. 



(Figs. 10 F, p. 108; 17 C, p. 228) 



Sporangium sessile, spherical, broadly ellipsoidal, or obpyriform, 

 with a broad rounded apex, 9-25 [x in diameter, becoming somewhat 

 angular upon the formation of from one to four projecting discharge 

 papillae, wall smooth, colorless; rhizoids broad, sparingly branched, 

 often undulate, invading as many as 70 host cells, up to 150 [x in length; 

 zoospores from ten to sixty or more, spherical, 2.5-3.5 [x in diameter, 

 with a colorless basal globule and a long flagellum, discharged through 

 pores formed upon the deliquescence of the papillae; resting spore 

 asexually formed, spherical, 5.4-9 ;jl in diameter, with a thick, smooth 

 wall and oleaginous refractive contents, germination not observed. 



Parasitic on Oscillatoria sp., Lyngbya sp., Dangeard (1884-85a: 88; 

 1886a: 294, pi. 13, figs. 1-5), France; Oscillatoria spp., de Wildeman 

 (1890: 17, fig. 5), Belgium; Oscillatoria sp., Minden (1915:323, fig. 

 14a-b), Germany; Oscillatoria sp., Sparrow (1936a: 439, pi. 17, figs. 

 1-2), Lyngbya sp., Ingold (1949:442), Oscillatoria agardhii var. iso- 

 thrix, Canter and Lund (1951:368, fig. 4, pi. 17, fig. C), Ingold (in 

 Canter and Lund, loc. cit.), Great Britain; Oscillatoria rubescens, 

 Oscillatoria sp., Canter (1953: 285), Canter and Lund (loc. cit.), Swit- 

 zerland; Oscillatoria sp., (Michigan) United States. 



See the discussion under Rhizophydium subangulosum, page 245. 



Ordinarily the sporangia are attached to the apical cells of the tri- 

 chomes, but they may be located elsewhere, the rhizoid then penetrat- 

 ing only one cell of the alga. The form illustrated by de Wildeman has 

 a subsporangial cylindrical prolongation into the host cell; the rhizoid 

 arises from this prolongation. A similar structure is found on an un- 

 named chytrid inhabitant o\^ Oscillatoria figured by Sparrow (1933c: 

 528, fig. I, 21). 



Canter and Lund (1951) give an illuminating account of the relation- 

 ship of this parasite of the planktonic Oscillatoria agardhii var. iso- 

 thrix to the increase in abundance of planktonic diatoms. 



