Striped Bum Coral

About

Striped Bum Coral (Heterocyathus aequicostatus) is one of the more unusual solitary corals you'll come across, and its biology is genuinely fascinating once you dig into it. Found across the Indo-Pacific on soft, silty or sandy seafloor habitats at depths typically starting around 20 metres, it lives a completely free-living existence rather than cementing itself to hard rock like most reef-building corals. A big part of why it can do this is a commensal sipunculid worm, Aspidosiphon corallicola, which takes up residence beneath the coral and slowly shuffles it around the substrate, preventing it from sinking or becoming buried. Essentially a built-in transport service. Each individual consists of a single circular corallite with well-defined ridges running down its sides, a flat base, and a coloration that runs toward pale brown with a greenish oral disc. Interestingly, this coral starts life by settling onto a tiny gastropod shell, which it gradually overgrows and envelops as it matures. Tentacles come out at night rather than during the day. Whether it hosts zooxanthellae or not can vary, which adds another layer of complexity for aquarium keeping. This one is best suited to keepers who enjoy the challenge of something genuinely out of the ordinary.