To form or become enclosed in a cyst (resting spore). There are several types of encystment. Stressed cells can 'round up' and settle out of the water column and yet be viable if the stress conditions are removed. Others involve temporary cysts for asexual reproduction, flotation, and other functional aspects of individual survival. Yet another type of encystment involves sexual reproduction and the production of thick-walled hypnozygotes which can remain encysted for months, even years (Steidinger and Tangen, 1996).