Encysted embryos (cysts) of the primitive crustacean, Artemia franciscana, are among the most resistant of all animal life history stages to extremes of environmental stress. These embryos, extremophiles of the animal kingdom, are the main focus of this paper. Previous work has revealed the importance of biochemical and biophysical adaptations that provide a significant part of the basis of their resistance, and I consider some of these here. In the present paper the critical role played by the outer layer of the shell in desiccation tolerance will be one focus. Another involves studies on the response of dried cysts to high temperatures that, among other things, implicate one or more volatile factors released from the cysts that determines the extent of thermotolerance under a given heating regime. A hypothetical scheme is given to account for these peculiar results. Based on western immunoblotting analysis, and data from the literature, the scheme also implicates the heat-induced translocation of the stress protein p26 to nuclei as a potential cause of the reduction in hatching level.