Did you know that although the fire coral is called a coral, it isn't really one. Fire corals are marine organisms that is often identified as a coral to majority. They are, in actual fact, more closely related to jellyfishes and stinging anemones. They are members of the phylum cnidaria, class hydrozoa, order cantata, family of the milleporidae. Fire corals have a bright yellow-green and brown skeletal outing and are widely found in tropical waters and subtropical waters. they appear in small bush-like groups on rocks and corals. Divers often mistake fire corals for seaweed accidental contact is common. The tiny nematocysts on fire corals tentacles that protrude numorous surface pores which similar to jellyfish stings. Also, fire corals have sharp, clacified external skeleton that can scrape the skin.

(source: http://en.wikipedia.org/wiki/Fire_coral)