On the outside, the Blue Coral (Heliopora coerulea) is brown. It is its internal skeleton that is blue, from where it derives its name. The Blue coral is a close relative to the soft coral even though it produces a hard skeleton. In fact, in the order of Helioporacea and subclass Octocorallia, it is the only species that produces a massive skeleton. This species of colonial coral is mostly found on the Southern shores. Its skeleton is composed of different calcium carbonates. Besides, there are tubes in the skeletons which have systems of canals and long, thin polyps. The polyps are white or beige and have tentacles.