Smooth Bum Coral

zooxanthellate

Corals are solitary or form small colonies, and are free-living with one or two calices on a base that is flat or keeled according to the nature of the substrate. They have an obligate commensal relationship with a sipunculid worm (Aspidosiphon corallicola) and usually have one parasitic mussel (Lithophaga lessepsiana) embedded above the sipunculid. The sipunculid moves the coral about on soft substrates and prevents it from becoming buried. Corallites are round or laterally compressed, up to 25 mm in diameter., have well-developed septa which follow Pourtales Plan, broad, compact deep-seated columellae, and walls composed of porous coenosteum. Polyps are extended only at night. They are hermatypic in tropical localities, but are possibly ahermatypic in high latitude locations. Colour: grey or brown. Abundance: always found on soft horizontal substrates at depths of 20 m or more. Where it does occur, it is usually very abundant (up to approximately 300 individuals per square ! (Veron, 1986 <57>) metre at some locations) Usually occurs in association with Heterocyathus aequicostatus and Cycloseris cyclolites. (Veron, 1986 <57>) An unusual, free-living coral, usually solitary or with two calices sharing one base. Overall size about 2-3 cm. Perforations in the base allow the commensal sipunculid worm (Aspidosiphon corallicola) to move in and out of the calyx. Habitat: on sand below the reef base. (Richmond, 1997)