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 polyps are yellow or orange, each with a fringe of about thirty very short tentacles surrounding a slit-shaped mouth.

[2] 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.

[3] 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.

Males liberate sperm into the sea and fertilisation takes place in the coelenteron (gastric cavity) of the female.