The nautilus is a living fossil, unchanged for hundreds of millions of years. Although divers see them infrequently, they are most common in the tropical western Pacific.

With impressive teeth and vibrant colors, titan triggerfish are the biggest among the species. And although they’re beautiful, divers should beware of this territorial fish.

Most corals are colonial animals with hundreds to thousands of tiny polyps, but solitary corals of the Indo-Pacific are a single-polyp species that lives freely on the ocean floor.

Octopus are one of the ocean’s most intelligent animals, and while it’s hard to pick favorites, here are the five species we most want to see on a dive.