Studies on British ChytridS. XXIX.A taxonomic revision of certain fungi found on the diatom Asterionella

Studies over a period of years have shown that two chytrids, morphologically very similar in the sporangial stage, occur on Asterionella formosa HasS. in certain lakes in the English Lake District. However, at dehiscence one is operculate and the other inoperculate. In the latter, part of the content of the sporangium flows out surrounded by a vesicle which soon bursts liberating the zoosporeS. It is now clear that both these species are included in the original description of the chytrid Rhizophydium planktonicum Canter. In so far as they are known, the life-histories of these two chytrids are described and discussed in relation to previous records of parasites on Asterionella. The inoperculate chytrid becomes R.planktonicum Canter emend, and the operculate one is designated as a new species, Zygorhizidium affluens (syn. R.planktonicum Canter pro parte). It is this operculate species which is mainly responsible for the epidemics which occur on Asterionella in Windermere, Blelham Tarn and Esthwaite Water. The hyper-parasite Rozellaparva sp.nov. , is also described; it parasitizes sporangia and resting spores of Z. Affluens .