KOTHOiiKI.I. \( I'.AK 



Chapter III 



Ectrogellaceae 

 Scherffel, 1925. Arch, IVotistk. 52: (i 



17 



Tin- family supercedes tin- Eurychasmaceae which 

 Petersen created in 1905 for the genus Eurychasma. 

 Because Petersen included hi* family in tin- Myxo- 

 chytridiales, with whicb it has little in common ix- 

 cept for its olpidioid holocarpic thalli, Scherffel re- 

 garded the Eurychasmaceae as invalid. Although he 

 placed Eurychasma and Ectrogella in the Saproleg- 



niaccae, he nevertheless suggested (p. <> ) that they 

 might comprise a separate family, the Ectrogel- 



laeeae. which he described as a group of simple 

 saprolegniaceous fungi the thalli of which are trans- 

 formed holocarpically into single zoosporangia. 

 Coker and Matthews ('•'!") incorporated Scherffel's 

 family in the Saprolegniales and added the genus 

 Aphanomycopsis which Scherffel had included in 

 the Saprolegniaceae. A similar interpretation was 

 made by Sparrow in 1983 and ]J)3<>. In his recent 

 classification of the aquatic Phycomycetes he 

 placed the Ectrogellaceae as the first and most 

 primitive family of the Saprolegniales and added his 

 in w genus Eurychasmidium to the group. Accord- 

 ing to his classification, this family includes Kctro- 

 gella, Eurychasma, Eurychasmidium, and Aphano- 

 mycopsis. Whether Aphanomycopsis belongs here 

 or in the I.agenidiaccae or Saprolegniaceae is open 

 to serious question. As will become more evident he- 

 low its thalli may he strikingly similar to those of 

 parthenogenetic species of Lagenidium. On the 

 other hand, it may also have the appearance of a 

 species of Aphanomyces in which sporangia are not 

 well differentiated. 



The suggested relationship of this family to the 

 Saprolegniaceae is based largely on the similarity 

 in method of zoosporogenesis. the presence of di- 

 planetism, and in the structure and behavior of the 

 zoospores, since evidence of sexual reproduction in 

 the Ectrogellaceae is at present very imager and 

 inconclusive. Resting spores are unknown in Eury- 

 chasma, Eurychasmidium and in all species of Kctru- 

 gella except E. Licmophorae and E. perforans. In 

 Aphanomycopsis tiny appear to he formed parthe- 

 nogenetically or merely by the contraction and en- 



cystment of the cell ( tent. In K. Licmophorae 



fusion of undifferentiated male and female thalli has 

 been reported, hut the evidence presented is not 



conclusive. 



ECTROGELLA 

 Zopf, 1884. Nova Acta KM. Leop.-Carol. Dent. 



Akad. Nat. 47 : 175. 



I'l. \TK S ) 



Thallus intramatrical, holocarpic, wall showing a 



more or less marked cellulose reaction when tested 



with chloro-iodide of zinc ; oval, elongate, cylindrical 



and vermiform; forcing the valves of the diatom 

 host apart at maturity. Zoosporangia single or num- 

 erous, hyaline, smooth, oval, egg-shaped, elongate. 

 cylindrical, vermiform and slightly irregular, some- 

 times becoming partially cxtramatrical at maturity, 

 with one to several comparatively short, wide, taper 

 ing exit tubes which project between the separated 



valves of the diatom cell. Zoospores variable in 

 shape, hyaline, with one to several small refractive 

 granules; usually hecoming active within the spo- 

 rangium; diplanetic, primary swarmers anteriorly 

 or laterally biflagellate and isocont. emerging singly 

 and swimming directly away as in Saprolegnia; or 

 aflagellate, gliding out and encysting in a group at 

 the mouth of the exit tube as in Achlya; secondary 

 swarmers oval, lemon-shaped, and pyriform, usually 

 with a ventral furrow, laterally biflagellate with the 

 flagella inserted nearer the anterior end ; the shorter 

 active flagellum directed forward and the longer one 

 backward in swimming. Resting spores hyaline, 

 smooth, spherical or oval, thick-walled with one 

 large or several smaller refractive glohules ; formed 

 parthenogenetically or by the fusion (?) of the con- 

 tents of a small male thallus or antheridium (?) 

 with that of female thallus through a hroad conjuga- 

 tion tube; germination unknown. 



This genus was first included in the Olpidiaceae, 

 hut since the discovery that the zoospores are bi- 

 flagellate and diplanetic it has been regarded, par- 

 ticularly by Scherffel, Coker and Matthews, and 

 Sparrow, as a primitive group of the Saprolegni- 

 ales. As it is here constituted Ectrogella includes 

 five species, some of which may possibly prove to he 

 identical from future studies. All are parasites of 

 diatoms and infect marine as well as freshwater spe- 

 cies. 



The life history and development of Ectrogella 

 Species arc shown in plate •"). The zoospores come to 

 rest on the host cell and put forth a germ tube which 

 soon penetrates the silicified wall of the host (fig. 1 ). 



The content of the spore then Hows into the host. 

 leaving the empty zoospore ease and penetration 

 tube behind. The young thallus is at first uninu- 

 cleate, naked and amoeboid with numerous pseudo- 

 pods ( fig. 2H ) hut becomes enveloped by a thin mem- 

 brane or wall very shortly after entering Hie host 

 cell. Multiple infection may frequently occur, so that 

 as many as thirty young thalli may occasionally be 

 found in a single cell. As the thalli develop the chlo- 

 roplasts of the host begin to lose their normal color, 

 disintegrate and break down. So far no direct en- 

 gulfing of masses of host protoplasm or discrete 



bodies by the thallus has been observed. With in- 



