A young olm, or proteus (Proteus anguinus) – an aquatic salamander – swimming in an aquarium in Postojna Cave, Slovenia, on Thursday. Olms are ancient underwater predators which can live up to 100 years and breed only once in a decade. They are resistant to long-term starvation, an adaptation to their underground habitat. In 2016, a total of 64 eggs were hatched in a rare occasion, with 21 olms surviving. The young olms are now slowly being released into an aquarium in the cave that is open to visitors.