Various types of coral, i.e. marine invertebrates living in compact colonies of several identical individual polyps, each with a set of tentacles around a central mouth.

Depending on the species, they either catch plankton and small fish with their tentacles, or they make use of photosynthesis to acquire energy and nutrients.

The polyps secrete calcium carbonate near their base, thus creating an exoskeleton characteristic of the species. Seen here, amongst others, are several Brain Coral. They get their name from the hemispherical shape with its distinctive grooved surface (fig.).