Brain Coral

These corals get their common name from the grooves and channels on their surfaces that look like the folds of the human brain. There's more than one kind of "brain coral"—several species from two different families of corals share the name—but all help build coral reefs.
Coral colonies are composed of tiny, anemone-like animals, known as polyps, which secrete the hard coral skeleton.

Reference:http://www.arkive.org/lesser-valley-coral/platygyra-lamellina/
http://animal-world.com/Aquarium-Coral-Reefs/Maze-Brain-Coral

Gif: underwater view of a brain coral off the coast of Miami.