Milne Edwards and Haime, 1848
Heterocyathus alternatus (3)
Type species: Heterocyathus aequicostatus Milne Edwards and Haime, 1848
Total number of species estimated: 4
Characteristics: Simple, fixed in neanic stage to a small univalve which it later completely covered by the base of the corallum except for a series of openings communicating with the chamber of the shell which serves as the burrow for a sipunculid (Aspidosiphon corallicola Sluiter), the whole adult symbiotic combination being free. No epitheca, the costae being continued over the base as a series of granulations, indicative of the canaliculate extensions of the intermesenterial chambers of the polyp. Septa following the Pourtalès plan. Columella papillose, papillae merging with the pali which stand before all septa cycles.
Key references: Hoeksema and Best, 1991.