Of major ecological importance is the ability of many organisms to survive reversible dehydration during one or more stages of their life history, a phenomenon known as anhydrobiosis. A diverse array of these organisms is found in aquatic habitats of temporary (ephemeral) nature that, when dry, can also reach high temperatures. Of significance in many regards, including basic science, agriculture and public health, these dried organisms are also among the most resistant organisms on Earth in terms of tolerance to very high temperatures and other environmental extremes. We restrict our coverage to anhydrobiotic eukaryotes because relatively little is known about their upper thermal limits compared to dried microorganisms.