CHYTRIDIALES 183 



KEY TO THE GENERA OF THE ACHLYOGETONACEAE 



Thallus forming typically a linear series of more than two sporangia 

 Zoospores encysting at the orifice of the discharge tube 



ACHLYOGETON, p. 183 



Zoospores clustering at, but eventually swimming directly away 

 from, the orifice of the discharge tube without encysting 



Septolpidium, p. 187 

 Thallus forming two sporangia, which are separated by a more or less 



well-defined isthmus Bicricium, p. 188 



ACHLYOGETON Schenk 



Bot. Zeitung, 17: 398. 1859 



(Fig. 15 A-B, p. 186) 



Thallus endobiotic, holocarpic, unbranched, without rhizoids, wall- 

 ed, at first tubular, later segmented and forming a chainlike series 

 of cells each of which develops a discharge tube and becomes an in- 

 operculate sporangium; zoospores posteriorly uniflagellate, with a re- 

 fractive globule, escaping as separate bodies and forming a motion- 

 less group at orifice of discharge tube, encysting, emerging from the 

 cellulose cysts after a period of rest and swimming away, the empty 

 cysts persistent for a time; resting spore not (?) observed. 



Parasites of green algae and eelworms. 



The similarity in body plan of Achlyogeton to Myzocytium has re- 

 sulted in the former's usually being placed in the Lagenidiales rather 

 than in the Chytridiales. This, as Butler (1928: 820) pointed out, has 

 been a cause of difficulty to those attempting to discover the true 

 affinities of these fungi. The flagellation of the spore marks the genus 

 as unquestionably a member of the Chytridiales. 



Karling (1942e: 94) doubted Schenk's observation that the zoospores 

 of Achlyogeton are posteriorly uniflagellate. This is a critical point, 

 for if they are proved to be biflagellate, the genus must once more 

 be returned to a biflagellate family, possibly the Lagenidiaceae, and 

 the family name replaced. In connection with work on a phycomycetous 

 parasite of insects considered to be Myiophagus ucrainica (Wize) Spar- 

 row 1 , Karling (1948a: 252) again questions the validity of Achlyo- 



1 The Myiophagus studied by Karling was in the sporangial stage only. Hence, its 

 identification with M. ucrainica, known only from the resting-spore stage, is open 

 to question. As Karling himself noted, his material might well be referred to a blasto- 

 cladiaceous fungus. 



