After much digging around I finally identified this amazing specimen as a cactus coral from the genus of Pavona. The small prickly pattern of polyp corallites was the best defining feature, as well as the folding plates that loosely resemble a cactus.

The Pavona, Cactus Coral is a small-polyp, stony coral which has been called, Cactus, Potato Chip, or Lettuce Coral.  A single species may vary in form according to the currents, wave action, lighting conditions and depth of its location. They can also vary in color from shades of light and dark brown to green with cream or white margins. Some have a fluorescent glow that can be seen beneath the polyps, giving these corals an interesting look. They are known to make a popular addition to the home aquarium.

CACTUS CORAL CLASSIFICATION

Kingdom: Animalia
Phylum: Cnidardia (A group containing over 10,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey by shooting off a threadlike, often toxic, tubule from inside the cnidocyst.)
Class: Anthozoa (Flower Animal)
Order: Scleratinia (Stony corals which are marine corals that generate a hard skeleton. They first appeared in the Middle Triassic and descended from the tabulate and rugose corals that barely survived the end of the Permian. Much of the framework of today’s coral reefs is formed by scleractinians. Stony coral numbers are expected to decline due to the effects of global warning and increased acidity due to pollution.)
Family: Agariciidae (Reef building stony corals including cactus corals, elephant skin corals, plate corals and lettuce corals.)
Genus: Pavona (Coral colonies of this type have vertical, irregular, two-sided fronds.)
Species: Possibly minuta or duerdeni