tached to the arthropod host by a basal holdfast. The holdfast is composed of an amorphous cement secreted from one end ofthe thallus through discrete pores (Whisler and Fuller, 1968). Amoebidium parasiticum is found on the external cu? ticle of a number of aquatic Crustacea (Branchiopoda, Amphipoda, Isopoda, Copepoda and Cladocera) and Insecta, including larvae of Dip? tera (Chironomidae, Culicidae), Ephemeroptera, Trichoptera, and in the rectum of Odonata (Lichtwardt, 1986). Contrary to the specific ep? ithet, the fungus does not penetrate the host cu? ticle and has not been reported to be parasitic. Amoebidium parasiticum was the first axenically cultured trichomycete (Whisler, 1960,1962). The fungus has been placed in the order Amoebidales (Lichtwardt, 1986) and may reproduce by amoeboid cells which encyst and form cytospores, or by sporangiospores. Typically, reproduction is by the sporangio? spore phase where growth occurs from a sporan? giospore to a mature thallus apparently in the presence of a low calcium ion concentration. Un? der standard culture conditions, the young thal? lus enlarges in size and nuclear number until the cell reaches a mature length of approximately 52 pm. The cytoplasm cleaves into approximately 13 diagonally elongated sporangiospores which increase in volume and rupture the sporangial wall (Whisler, 1968). In the alternate reproductive pathway amoebae are produced instead of sporangiospores. In this pathway, under culture conditions, the thallus enlarges in volume and nuclear number until the cell reaches a length of approximately 45 pm, at which time a transverse cytoplasmic cleavage occurs, in contrast to the diagonally oriented cleavage of sporangiospore formation; in nature there can be sizable varia? tion in thallus dimensions. No wall forms around the cleaved units, and as the thallus wall ruptures, naked amoebae escape. Following a period of active migration, the amoebae become rotund and inactive and deposit a wall to form a cyst (Whisler, 1966,1968). Whisler (1966,1968) outlined several factors which may induce A. parasiticum to switch from the sporangiospore phase to the amoeba-cyst phase in its life cycle under laboratory conditions. A dialyzed extract of daphnids (of unknown composition) induced amoebagenesis. A pH value near 8, and a tem? perature near 30 C and a relatively high calcium concentration (about 0.01 M) were optimal for amoeba formation.