Helioporacea is an order of the subclass

Octocorallia Octocorallia (also known as Alcyonaria) is a class of Anthozoa comprising around 3,000 species of water-based organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians (sea fans ...

that forms massive lobed

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

skeletons in colonial corals. These corals first appeared in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period. It consists of two families, Helioporidae Moseley, 1876Moseley, H. N. (1876). On the structure and relations of the alcyonarian ''Heliopora caerula'', with some account of the anatomy of a species of ''Sarcophyton'', notes on the structure of species of the genera ''Millepora'', ''Pocillopora'', and ''Stylaster'', and remarks on the affinities of certain palaeozoic corals. ''Philosophical Transactions of the Royal Society of London'', 166, 91–129. and Lithotelestidae Bayer & Muzik, 1977.Bayer, F. M. & Muzik, K. M. (1977). An Atlantic helioporan coral (Coelenterata: Octocorallia). ''Proceedings of the Biological Society of Washington'', 90(4), 975–984. The

blue coral Blue coral (''Heliopora coerulea'') is a species of colonial coral. It is 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 ...

(''Heliopora coerulea''), the only extant species in the family Helioporidae, is most common in shallow water of the tropical Pacific and Indo-Pacific reefs. It has no spicules, and is the only octocoral known to produce a massive skeleton formed of fibrocrystalline

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

fused into

lamellae Lamella (plural lamellae) means a small plate or flake in Latin, and in English may refer to: Biology * Lamella (mycology), a papery rib beneath a mushroom cap * Lamella (botany) * Lamella (surface anatomy), a plate-like structure in an animal * ...

, similar to that of the

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a ...

(stony corals). They form large colonies that can exceed a meter in diameter. They are composed of vertical branches, or

folia ''La Folía'' (Spanish), or ''Follies'' (English), also known as ''folies d'Espagne'' (French), ''La Follia'' (Italian), and ''Folia'' (Portuguese), is one of the oldest remembered European musical themes, or primary material, generally melodic, ...

. The surface of blue coral and similar species appears smooth and the color in life is a distinctive grey-brown with white tips. The entire skeleton, however, has an unusual blue color and therefore the species is commonly exploited for decorative uses. The blue color of the skeleton (which is covered with a layer of brown polyps) is caused by iron salts. Blue coral can be used in tropical aquaria, and the crystalline calcareous fibres in the skeletons can be used for jewelry. Individual polyps have eight feathery tentacles and, in the

gastrovascular cavity The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into a ...

, eight septa, or partitions. Cilia (tiny hairlike projections) on six septa draw water into the cavity. Cilia on the other two septa expel water. The skeleton consists of spicules that form a protective cup around each polyp.

References

Octocorallia Cnidarian orders {{octocorallia-stub