The body of an octopus is remarkable enough. The common octopus, O. vulgaris, has eight armlike appendages, three hearts pumping blue blood, an ink-based defense mechanism, and highly developed jet propulsion. An octopus can change size, shape, texture, and color at will, and all at the same time if necessary.

The number of species that can be found on a healthy patch of reef is probably greater than can be encountered in a similar amount of space anywhere else on earth, including the Amazon rainforest. Researchers once picked apart a single coral colony and counted more than eight thousand burrowing creatures belonging to more than two hundred species.