Lesser Knob Coral

Found over a wide range of reef habitats, this is one of the most common stony corals.
Colonies are massive to smaller column shapes, with a smooth or hillocky surface. Tentacles only extended at night.
Colours vary from cream, brown, and grey.

Stony corals have hard stony skeletons, their polyps have six tentacles or are made up of multiples of six. These are usually nocturnal, however if the sky's are overcast, then many will feed during the day.
Generally the more robust corals life on exposed areas, while the smaller corals live in sheltered lagoons or deeper waters.
Stony corals are reef building corals and embedded in their flesh are thousands of minute single-celled marine plants called zooxanthellae which accounts for their colour.
These corals support a huge diversity of life, their main predator being the crown-of-thorns sea star.