NATURE lifts part of the veil of mystery shrouding some fascinating -- and often fearsome -- creatures in THE SECRET WORLD OF SHARKS AND RAYS.

Sharks and their biological cousins, the rays, are among the highest-profile denizens of the deep, thanks to the popularity of books and films that have cast them in leading roles -- as antagonist, not protagonist.

But despite such worldwide media glare, sharks and rays are among the least-understood creatures that inhabit the world's oceans. It's a paradox: a high public profile overshadowing a relatively low level of knowledge about these primordial fish, whose existence pre-dates the emergence of humans by some 400 million years.