Corals are of many different sizes, forms and colors and it is estimated that there are over 2500 species of corals. Like all species belonging to the Class Coelenterata they have arrow cells (nematocystes) used in defense.

Man can be injured by contact with certain species, which have sharp extensions causing various types of wounds.

Some species cause more irritation than others, which is for instance the reason on is called "Fire Coral", of the family Milleporidae. When touched they discharge their arrow cells, releasing their irritating toxin: this will produce a pain with a burning sensation, reddening of the skin (sometimes marking the contour of the coral), itching, etc.

For that reason when diving among corals, we should admire their beauty and not touch them; avoid swimming in shallow areas of coral reefs, and if for some reason we have to touch them we should use the correct protection (gloves).

It is very important not to destroy them and to take care of them, for that reason we should not stand on them or throw heavy objects on them; in this way we help their preservation.