Mastigias papua, the lagoon jellyfish (family Mastigiidae), is a rhizostome scyphozoan distributed across shallow tropical lagoons and semi-enclosed bays of the Indo-Pacific. Its bell is covered in white spots representing zooxanthellate tissue masses, and its highly branched oral arms harbor dense Symbiodiniaceae populations providing photosynthetically derived nutrition supplementing filter feeding. The species is best known from isolated marine lake populations in Palau and other Pacific islands studied as examples of convergent evolution and symbiosis biology. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.