Although tabulate corals, which occur in limestone and calcareous shale, became extinct on Earth during the late Permian Era (being replaced by scleractinian corals), these flourish on the new planet as it remains in the Carboniferous Era when these forms filled the shallow oceans. Corals are animals, with a tubular morphology: the lower end anchored to a stable surface and the other surrounded by small tentacles for gathering food. On this planet, these corals range up to 30mm in diameter, and can grow up to a half millimeter per year depending on age, food supply and water temperature. With outer skeletons composed of calcite, the tabulate corals form vast low cushions or branching masses as reefs, populated by a wide variety of salt-water echinoids, brachiopods, bivalves and gastropods. Although some tabulate corals can trap small invertebrates and plankton with their tentacles, most feed on photosynthetic algae. On Earth, coral – or rather the massed skeletons of coral colonies – was used extensively for jewelry and cosmetics, and in some places (such as East Africa) as a source of lime for construction; this is still the case among many colonists, but research by Polystralian ecologists and others have found many profitable methods of using coral to promote aquaculture on a commercial scale.