LAG EN IDI ALES 919 



L. humanum (Karling, 1947c), and Sirolpidium zoophthorum Vishniac 

 (1955b) have been grown on artificial media. Diehl (1935) reported the 

 cultivation to maturity of some immature thalli of Olpidiopsis which 

 had been removed from their saprolegniaceous host to artificial media. 

 Species of Olpidiopsis and Rozellopsis are, with the exception just 

 noted, obligate parasites of aquatic Phycomycetes and of a few fresh- 

 water and marine algae. An experimental study of certain species of 

 Olpidiopsis (Shanor, 1940) indicates that they are restricted to relatively 

 few host species (see discussion under Olpidiopsis, p. 928). Pseudolpidium, 

 Rozellopsis, and Pseudosphaerita also are, so far as is known, obligate 

 parasites of particular hosts. Species of Petersenia, a marine genus, may 

 possibly at times be weakly parasitic on certain marine red algae and 

 initiate the destruction of the alga, but after the death of the host they 

 can maintain themselves as saprophytes (Sparrow, 1934c, 1936b). 



Sirolpidium and Pontisma, inhabitants of marine algae, perhaps act as 

 parasites in early stages of infection, but for the major part of their 

 development they live as saprophytes (Sparrow, 1934c, 1936b; Aleem, 

 1953). 



Myzocytium and Lagenidium (with the exception of L. giganteum and 

 L. humanum) are at present thought to be obligate parasites of their 

 hosts. They occur primarily as parasites of the Conjugatae, attacking 

 both vegetative and reproductive cells. Other species are found in eel- 

 worms, the eggs, embryos, and adults of rotifers, and so forth, and on 

 pollen grains. As is true of the chytrids, practically no significant exper- 

 imental work has been thus far attempted to ascertain the range of hosts 

 which a single fungus will attack, and claims of host specificity rest for 

 the most part on observations of findings in nature. 



SYSTEMATIC ACCOUNT 



LAGENIDIALES 



Microscopic, primarily parasitic aquatic fungi of simple body plan or 

 with a septate mycelial development of slight extent, the thallus endo- 

 biotic, holocarpic, forming one or more reproductive organs, without a 

 specialized vegetative system, at first unwalled ("plasmodial") or walled, 

 the walls generally giving a cellulose reaction, infection tube persistent 



