Heteropsammia are a unique group of stony corals which do not attach to the substrate. These free living corals have a flat base, and live in calm sandy areas, usually in the depths outside of the coral reefs. With many of the species of Heteropsammia, the larvae settle down onto the shell of very small snails, which are then engulfed as the coral grows. They also have an obligate commensal relationship with a small worm, known as a sipunculid, which protrudes from a small hole in the bottom of the coral and helps the coral right itself, move around, and prevents it from being buried in the sand. Because this worm can also move the coral around, the corals are known in the aquarium trade as “Walking Dendros.”
Almost the entire upper portion of the 2.5 cm wide coral is a mouth, meaning that it is able to consume much larger prey than most other hard coral species. Being a coral which lives deep, this is an advantage as there is less light available at depth to power photosynthesis for the coral’s symbiotic algae. These corals thus rely more on predation than the functionally autotrophic corals of the shallow oceans. But what exactly do they eat is a question that is still being answered. Recently, on the island of Koh Tao in the Gulf of Thailand, the corals have been observed eating salps, an observation that was recently published in the Journal of Marine Biodiversity.