Adding to the above: Cnidarians have stinging cells. Amply demonstrated by jellyfish, however Anemomes also sting. Though the sting of anemones is usually harmless, there are very toxic specimans whose venom is a mix of toxins and neurotoxins, that can cause serious injuries and can be fatal. This is in addition to palytoxin which is actually one of the most lethal non-peptide substance known, second only to maitotoxin. (in rats anyway) However, the most common route of palytoxin poisoning in humans is by ingestion, and the action of the toxin is swift and death follows quickly; there are several avenues of exposure, and the LD50 differs with differing routes of exposure. The dreaded limu-make-o-hana ...that is actually a soft coral (Walsh and Bowers 1971,) and palytoxin is most associated with certain marine species, though spreads by accumulation, and ovatoxin-a a marine aerosol produced by the tropical microalga, the dinoflagellate Ostreopsis ovata caused hundreds of poisonings in Geneoa, Italy, in 2005 and 2006. However, the palytoxin poisoning worries are a bit exaggerated in general, though very real.
