When it comes to our favorite ocean animals, I think it’s safe to say octopuses are very high on the list. Here at Ocean Conservancy, we just can’t get enough of cephalopods. They are unique, interesting and mesmerizing. And, just when you think you’ve learned all about them—you find out something new!

The marine animal class of Cephalopoda includes octopuses, squid, cuttlefish and nautiluses. The name “cephalopod” comes from the fact that their arms are connected directly to their heads. Octopus have eight arms, while squid and cuttlefish have eight arms plus two other specialized appendages called tentacles.

You’ve heard of monsters of the deep—but which cephalopod is the biggest? Which is the true monster lurking in the sea? Let’s dive in and find out if it is colossal or giant!

Seven-armed octopus

Up to 11 feet long

The seven-armed octopus is one of the largest known species of octopus. It can reach lengths of up to 11 feet long. But don’t let its name fool you! It is a true octopus with eight arms. But, in the males, one arm is hidden except during mating. Found in the deep sea, the seven-armed octopus lives in the Pacific Ocean.

Giant Pacific octopus

About 12 feet long

The giant Pacific octopus is the largest and longest-living of all octopus species. On average, they are about 12 feet in length and weigh more than 50 pounds. Giant Pacific octopuses are venomous. (All octopuses and cuttlefish are venomous.) They inject their venom into prey through their sharp beaks. The giant Pacific octopus is incredibly smart and can learn to solve mazes, open jars, recognize people’s faces and even escape enclosures.

Colossal squid

Around 40 feet long

It’s not quite the longest, but scientists believe the colossal squid weighs more than the giant squid. The colossal squid is found in deep marine environments in the waters around Antarctica, but it may come as far north as the southern waters of New Zealand. Very little is known about colossal squid. They are very rarely captured or seen. Scientists first documented colossal squid in 1925 when the head and arms were discovered in a sperm whale stomach. Since then, a total of only eight adult colossal squid have been reported, six of which were recovered from the stomachs of caught whales.

Giant squid

More than 40 feet long

If you measure all the way out to the tip of their two long feeding tentacles, the giant squid measures more than 40 feet long! To put that into perspective, that is longer than a school bus. Giant squids have the largest eyes in the animal kingdom. They live in the deep sea where it is so dark that they need very large eyes to pick up any amount of light that passes through to that depth. Giant squids are elusive creatures, and because they live at such great depths of the ocean, humans rarely encounter them. They have lived throughout the ages through stories of sea monsters and supposedly tall tales. Some believe that the terrible Kraken of ancient myth may have been partly based on the giant squid.

You Can HELP

Climate change could negatively affect cephalopods through warming temperatures that disrupt egg development, acidification that harms prey items and hypoxic zones that decrease available habitat. Consider making a donation to Ocean Conservancy today—give today and make a difference for the future of our ocean!