804 AQUATIC PHYCOMYCETES 



panied (in one species) by a companion cell, germination not observed. 



Parasites of fresh-water and marine diatoms. 1 



A relatively poorly known group of minute parasites. Zopf stated 

 that the zoospores were posteriorly uniflagellate, but Scherffel has shown 

 them to be biflagellate and diplanetic. The genus as understood here is 

 confined to parasites of diatoms. Scherffel (he. cit.), however, suggested 

 the inclusion of the phaeophycean parasite Euryehasma in Ectrogel/a. 



The discharge tubes of Ectrogel/a, rather than boring through the 

 siliceous wall of the diatom, gain access to the outside by expansion of 

 the thallus, which forces apart the valves of the host. 



KEY TO THE SPECIES OF ECTROGELLA 2 



Sporangium narrowly tubular, with or without an equatorial swelling, 

 discharge tubes short 

 Sporangium predominantly narrowly tubular throughout, discharge 

 tubes numerous; primary zoospores flagellated and undergoing 

 a short period of motility before encysting 



E. bacillariacearum, p. 805 

 Sporangium predominantly tubular, with an equatorial swelling, 

 discharge tube single; primary zoospores nonflagellate, encyst- 

 ing at the orifice after discharge E. monostoma, p. 807 



Sporangium predominantly broadly cylindric-oblong, flattened ellip- 

 soidal, or ovoid, or lenticular or spherical, discharge tubes of 

 variable length 

 Sporangium broadly cylindric-oblong, or ovoid; primary zoospores 

 nonflagellate, encysting at the orifice after discharge 

 Sporangium predominantly broadly cylindric-oblong, discharge 

 tubes short, generally two, placed near one end of the spo- 

 rangium; in Gomphonema E. gomphonematis, p. 807 



Sporangium predominantly ovoid, discharge tubes slightly pro- 

 longed, from two to ten, often opposite, formed at any place 



on the sporangium ; in Licmophora E. licmophorae, p. 808 



Sporangium predominantly spherical or lenticular or flattened ellip- 

 soidal; zoospores swimming directly away after escape 

 Sporangium predominantly spherical or lenticular; in marine 



species of Licmophora E. pcrforans, p. 809 



Sporangium predominantly flattened ellipsoidal; in fresh-water 



Eunotia E. eunotiae, p. 810 



1 See, however, Ectrogella marina on Chlorodendron subsalsum (J. and G. Feld- 

 mann, 1955: 238). p. 811. 



- See also recently described taxa, p. 81 1 . 



