Phyllodiscus semoni is a morphologically variable sea anemone species from the Indo-Pacific with morphotypes ranging from upright and branched to low-lying and rounded. The apparent camouflage strategies of this sea anemone allow it to resemble other species or objects in its environment, such as stony corals, soft corals, seaweeds, or rocky boulders covered by algae, which may help it to avoid recognition by potential predators. Occasionally, it occurs in aggregations that may result from asexual reproduction. A high level of intraspecific morphological variation, including co-occurring aggregations of three different morphotypes, was observed in the Spermonde Archipelago off Makassar, South Sulawesi, Indonesia. The co-occurrence of aggregations with different morphotypes suggests that Phyllodiscus is a highly polymorphic monospecific genus. Sea anemones of this genus are not frequently encountered at other localities and the number of morphotypes seems large. Therefore, it is unlikely that we are dealing with more than one species that are all concentrated in a single area. Phyllodiscus sea anemones are considered dangerous to humans because their nematocysts contain highly toxic venoms that may inflict harmful stings. Therefore they are the subject of recent toxicological studies. The present paper aims to assist in the recognition of these highly variable hazardous animals and to discuss the appearance of their aggregations.