Palythoa toxica

P. toxica is an encrusting species with a firm, tough cuticle.[5] The polyps are partially embedded in a cushiony mat of coenenchyme which grows across the rock surface, and which incorporates sand grains and fragments of debris. The oral disc of each polyp is broad and has a fringe of tentacles. The polyps can close up and be retracted into the coenenchyme, which then displays a pitted surface. The colour of this species is variable but is usually some shade of cream, grey or pale brown.[6][7]

A Hawaiian legend relates how in a rock pool in the Hana district on the island of Maui there was to be found an alga known to the locals as "limu-make-o-Hana" ('seaweed of death from Hana'). The exact location of the pool was known to only a few individuals and visiting it was taboo. In 1961, intrigued by this, researchers searched for the location and discovered the zoanthid.[8] Although advised by local people not to do so, they took some specimens away with them. On that very day, the laboratories of the Hawaiian Institute of Marine Biology on Coconut Island, Oahu were destroyed by fire.[3] The toxic effects of this species were known to the early inhabitants of Hawaii, and the zoanthids were applied by them to the tips of their weapons,[5] or according to one account, under severe threat, the warriors could overcome the taboo and dip their spear tips into the pool for them to become lethal.[9]

P. toxica was first discovered in the small district of Muolea on the island of Maui in Hawaii. Its habitat was a shallow pool about 10 in (25 cm) deep which was subject to inflows of fresh water during periods of heavy rainfall, so it would appear to be a euryhaline species.[10] The zoanthid has since been discovered in a few other locations in the Hawaiian islands.

P. toxica contains palytoxin, one of the most poisonous substances known.[9] This zoanthid is not the only member of its genus to contain the toxin; that distinction is shared by P. tuberculosa. The latter species has a seasonal cycle, varying in toxicity at different times of year, whereas P. toxica is equally toxic all year round.[10] Other species of Palythoa have also been shown to contain the substance in varying amounts at different times and in different places, and some algae and certain crabs and fish have been found to contain it. It has been suggested that the toxin is actually produced by a dinoflagellate, Ostreopsis spp., and incorporated into the zoanthid tissues, possibly through a symbiotic relationship similar to that of zooxanthellae in coral.[11]

Fishkeepers keep P. toxica and other species of the genus in reef aquariums.[6][7] This practice has led to poisonings of hobbyists who have carelessly handled the organisms.[12][13][14][15][16]