970 AQUATIC PHYCOMYCETES 



This is the fungus described by Davis, Loosanoff, Weston, and 

 Martin (1954) as the cause of a serious epidemic of clam and oyster 

 larvae in culture. 



Ganaros (1957) has reported a fungus, allied either to this species 

 or to Plectospira dubia, as the cause of the destruction of eggs of the 

 oyster drill, Urosalpinx cinerea, in Connecticut. 



PONTISMA H. E. Petersen 

 Oversigt Kgl. Danske Vidensk. Selskabs. Forhandl., 1905(5): 482 



(Fig. 78, p. 969) 



Thallus endobiotic, holocarpic, without specialized vegetative struc- 

 tures, consisting of an unbranched or irregularly branched tube of small 

 extent, which at maturity becomes segmented, the segments few in 

 number, occasionally olpidioid or tubular and nonseptate, contents at 

 first vacuolate, later with numerous refractive granules, walls giving 

 a cellulose reaction; sporangia formed from the segments, each bearing 

 a single discharge tube (sometimes several), the tip of which, at least, is 

 extramatrical; zoospores minute, pyriform, with a refractive body at 

 either end and two oppositely directed flagella, completely formed 

 within the sporangium, where motility is initiated, swimming individ- 

 ually through a pore at the tip of the discharge tube; resting spore 

 spherical and thick-walled with several refractive oil drops. 



In Ceramium spp. 



The genus resembles Sirolpidium in the segmentation of the thallus, 

 but differs in being branched and in not exhibiting fragmentation. 



Pontisma, so far as is known, occurs primarily, if not exclusively, in 

 the marine alga Ceramium. The thallus is difficult to characterize 

 precisely because of its "generalized" aspect. Penetration of the zoo- 

 spore and the very early stages in the establishment of the thallus have 

 not been observed. 



Contrary to Karling's (1942e:63) belief that Pontisma should be 

 merged with Sirolpidium, actual observers of the fungus (Petersen, 

 Sparrow, Aleem, Hohnk, and Kobayashi and Ookubo) regard it as 

 distinct from that unbranched, fragmenting form. Until the resting 



