New observations on scleractinian corals from Indonesia: 2. Sipunculan-associated species belonging to the genera Heterocyathus and Heteropsammia

Three Indonesian species of Heterocyathus and two of Heteropsammia are briefly diagnosed. Remarks are given on their synonymy, phenotypic variation, and ecology. All five species are found on soft substrata in the proximity of coral reefs and live in association with a sipunculan worm. This interspecific assocation is discussed with regard to whether it is mutualistic or parasitic.