Lesser Starlet Coral

Siderastrea radians is either encrusting or grows in small, dimpled hummocks up to 30 centimetres (12 in) across but most colonies are much smaller than this. Occasionally it occurs as small calcareous pebbles that roll around in seagrass meadows or as loose flat discs in shallow rocky places. The corallites are not circular but are triangular or four-sided and deep, with 30 to 40 small ridges called septa. They have a dark interior that contrasts in colour with the pale surface of the coral which is greyish, greenish or light brown. The polyps are retracted back into these corallites during the day but emerge at night, extending their tentacles to feed. Each of these has a small knob of stinging cnidocytes at its tip.

Siderastrea radians is common in tropical parts of the western Atlantic Ocean at depths of less than 25 metres (82 ft) but is most common in under 10 metres (33 ft) of water. Its range extends from Bermuda, the Bahamas, Florida and the Caribbean Sea south to Brazil and it also occurs in the eastern Atlantic off the coast of Africa. It is found on rocks in various reef habitats and can tolerate silty environments and tide pools. It is an adaptable species and in the Indian River Lagoon it has been found to tolerate temperatures varying between 13 °C (55 °F) and 31 °C (88 °F) and a wide range of salinities.