Cassiopea andromeda, the upside-down jellyfish (family Cassiopeidae), is distributed across shallow, warm coastal waters of the Indo-Pacific, resting bell-side down on sandy or muddy substrates and exposing its highly branched oral arms to sunlight to maximize photosynthesis by its endosymbiotic Symbiodiniaceae. The species produces a mucus cloud containing stinging cassiosomes that can cause dermatological reactions in swimmers without direct contact. A genome has been assembled for C. Cassiopea species are increasingly studied as models for cnidarian sleep-like states and photobiology.