Intelligent Invertebrate: The octopus — a cephalopod — is one of the largest, fastest and most intelligent of all invertebrates. Its body is rounded with long tentacles lined with powerful suckers that it uses for gripping prey and mobility. Its eyes are humanlike and adept at spotting the next meal.

From Top to Bottom: The octopus is usually a bottom dweller, but some species will use the currents along the bottom of the seabed to move from place to place. The octopus is not very maternal; as eggs hatch, the mother will blow the young out of the den. The young octopuses swim to the surface and float among the plankton for a few months until they're ready to sink to the seabed and begin their life as an adult.

One Enormous Octopus: The world's largest octopus species is the giant Pacific octopus. It's not uncommon for these giants to reach over 16 feet in length and weigh more than 110 pounds. When threatened, the giant Pacific octopus flees behind a cloud of ink.