Staghorn coral (Peter Leahy / shutterstock.com)
Sea anemones and corals are cnidarians (anthozoa) without free-swimming life stage. While a coral is a colony of myriads of identical polyps, a sea anemone is a single organism. Most corals obtain nutrients from symbiotic photosynthetic algae known as zooxanthellae. Skin contact with fire corals (technically no true corals) causes severe pain that can last for several days. Full neoprene or Lycra suits provide adequate protection.
Some species venomous.