What is "blue coral"

Heliopora \He`li*op"o*ra\, n. [NL., fr. Gr. ? the sun + ? a passage, pore.] (Zo["o]l.) An East Indian stony coral now known to belong to the Alcyonaria; -- called also blue coral.

Blue coral (Heliopora coerulea) is a species of colonial coral and the only species in the family Helioporidae and the only Octocoral known to produce a massive skeleton. This skeleton is formed of aragonite, similar to that of scleractinia. Individual polyps live in tubes within the skeleton and are connected by a thin layer of tissue over the outside of the skeleton. It was described by Pallas in 1766.