Zoanthus gigantus is a large-polyped zoantharian (family Zoanthidae, order Zoantharia) found in shallow tropical Indo-Pacific reef environments, forming encrusting colonial mats with notably large polyps compared to most other Zoanthus species—a characteristic reflected in its specific epithet. Like other Zoanthus species, it lacks a calcareous skeleton and forms flat encrusting colonies on hard substrates, reef rubble, and dead coral. Zoanthus species are popular in the marine aquarium trade and are studied for their diverse secondary metabolite chemistry. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.