Star Coral

Astroides calycularis is a colonial coral, consisting of a group of polyps, each of which sits in a stony cup known as a calyx. The colonies are 25 to 30 cm (10 to 12 in) in diameter and 10 cm (4 in) high and each polyp is about 1 to 2 cm (0.4 to 0.8 in) in diameter. The polyps are yellow or orange, each with a fringe of about thirty very short tentacles surrounding a slit-shaped mouth. The colony grows by asexual reproduction, new polyps budding off existing polyps and secreting their own calices. Deep-water colonies are bush-shaped, the calices are circular and budding occurs at various heights on the calyx walls. Shallow-water colonies tend to be ellipsoid in shape, the calyces are polygonal and budding occurs in the centre of the colony as well as round the edges.

During the Pleistocene, Astroides calycularis had a wider distribution than it does now, and was present in the whole of the western Mediterranean. Since then it has disappeared from the northern part of that range as a result of the lower sea temperatures that resulted from glaciation. Nowadays it is native to the part of the western Mediterranean Sea that is south of Sardinia and is also present in the Atlantic Ocean near the Strait of Gibraltar. Before 1989 it was restricted to the area west of Sicily, but in that year it appeared in the Adriatic Sea for the first time. This coincided with a sudden change of circulation in the eastern Mediterranean which may have allowed the short-lived pelagic larvae to survive long enough to settle on the seabed of the Croatian coast. A.