Blue coral

Blue coral in an aquarium

The Blue Coral ( Heliopora coerulea ) lives in coral reefs in the Indo-Pacific, looks like a coral stone, however, is the last survivor of a group of Octocorallia, which was only known fossil first. Very similar shapes with an age of 100 million years have been known for the Cretaceous of the coasts of the Tethys from Europe, Africa and India. It is the only species of Octocorallia, which forms a massive skeleton of calcium carbonate. The Blue Coral comes in the Indo-Pacific, only in regions that have a constant temperature of 22 ° C or more.

Features

The colonies can form powerful blocks with plate-like branches, a height of half a meter and a diameter of seven meters. Reaching the blocks the water surface, so dies the falling dry tissue and form micro atolls.

Outside the colonies are brown in color, the skeleton is colored blue due to various iron salts. The Blue Coral polyps are small, only a millimeter size, and like all Octocorallia eight feathery tentacles. The skeleton is not, as in other Octocorallia formed by sclerites, which are then connected to each other, but by fibers of aragonite, which merge to form thin platelets. The polyps sit in niches in the skeleton are connected by stolons and encapsulate the niches with the further skeletal growth by transverse walls to bottom. In addition to the polyps niches there are small pore-like niches, in which the root -like Stolonengewebe grows downward. The living tissue forms only a very thin layer on the Aragonitskelett.

The Blue coral lives in symbiosis with zooxanthellae, single-celled algae from the group of dinoflagellates, which supply the coral with nutrients.

System

Traditionally, the Blue Coral is asked for their uniqueness in its own order, the Helioporacea. Phylogenetically it is the sister species to a clade from the sea pens ( Pennatulacea ) and the Gorgonienfamilie Ellisellidae. The clade formed by these three taxa is the sister group of the Calcaxonia, a subordination gorgonienähnlicher corals.