Mastigias albipunctata, the spotted jellyfish of Palau's Jellyfish Lake (family Mastigiidae), is a scyphozoan rhizostome medusa famous for its isolated population in the marine lake Ongeim'l Tketau on Palau's Rock Islands. This landlocked population has lived isolated from open-ocean predators for thousands of years, evolving reduced nematocyst potency as predator defenses became unnecessary. The species harbors photosymbiotic Symbiodiniaceae and undertakes daily horizontal migrations to optimize photosynthetic exposure. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.