Acropora

Acropora is a genus of small-polyp stony coral in the phylum Cnidaria, colonial animals made up of individual polyps about 2 millimeters across that share tissue and nerve networks and grow as plates or as slender or broad branches depending on species and location. More than 149 species have been described, though the true number remains uncertain because of hybridization and cryptic species complexes; polyps retract when disturbed by predators but otherwise extend to capture plankton, especially at night. Acropora corals are major reef builders responsible for much of the calcium carbonate substructure of coral reefs, with species concentrated in the Indo-Pacific, home to more than 100 species, and a smaller number in the Caribbean.