Astroides

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 in diameter and high and each polyp is about 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. ==Distribution and habitat==

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. A. calycularis is found on rocks and walls, under overhangs and in submarine caves at depths down to about . In suitable locations, colonies can cover 90% of the available substrate. ==Biology==

Astroides calycularis is nocturnal, the polyps remaining retracted back into their calices during the day. When expanded at night, they feed on zooplankton, small fish and perhaps bacteria. This coral is azooxanthellate, meaning it does not contain symbiotic dinoflagellates in its tissues as do many species of coral. A. calycularis colonies are gonochoristic with all the polyps in a colony being of the same sex. Males liberate sperm into the sea and fertilisation takes place in the coelenteron (gastric cavity) of the female. The eggs have yolks, and the embryos are brooded in the coelenteron until they are liberated into the water column as planula larvae. ==References==