A Humboldt squid rockets up out of the darkness, meeting Bob Cranston in the middle of a cloud of krill.

(Airs Sunday, June 28) Underwater cameraman Bob Cranston explores the remarkable world of marine creatures called cephalopods -- squids, cuttlefish, octopi, and nautili.

With its fascinating coloring and delicate curling arms, the blue-ringed octopus may be a beautiful creature, but this small cephalopod is also deadly.

Cuttlefish, along with octopuses and squid, are cephalopods — animals from an ancient branch of the tree of life that have been trolling the oceans for more than 500 million years.

Bob Cranston waved off advice from local fishermen and caught some of the most memorable footage ever captured of the giant and aggressive Humboldt squid.

Meet Dr. Mark Norman, one of the world's leading octopus experts, who is also featured in "Encountering Sea Monsters."

Find additional resources, online and in print, on squids, octopi, and other cephalopods.

A new age of ocean exploration is lifting the veil of mystery shrouding a creature of legend -- the octopus.

Octopuses also exhibit behaviors -- from neon-bright flashing skin colors to breathtaking jet-propelled swims -- that have made scientists sit up and take notice.