It's World Octopus Day! Here Are Eight Awesome Octopodes

It's World Octopus Day! Raise your eyes, raise your voices and proclaim the gospel of the octopus! Romeo Ranoco / REUTERS

Hooray—it's world octopus day. Today we celebrate the excellent eight-legged creatures that grace our oceans, and occasionally even venture out of the water. (Even Aristotle knew: "the only cephalopod to go out on to dry land is the octopus.") What other animal has three hearts, a brain-like set of nerves in each leg and blue blood? What other 50-pound beast could fit through a two-inch hole?

None, I tell you. Without further ado, here are our choices for the eight most awesome octopuses out there.

A closeup of a giant Pacific octopus, the world's largest species. Quadell via Wikimedia Commons

The giant Pacific octopus

This species (Enteroctopus dofleini) is the largest in the world, and found from the United States's Pacific Northwest to the coast of Japan. Specimens have been measured more than 16 feet in length and weighing up to 600 pounds (272 kilograms), though most weigh considerably less. Each of its legs also holds up to 280 suckers.

An average giant Pacific octopus female can lay 90,000 eggs. Like most octopuses, she will die shortly after laying them.

These animals are found in tidal pools and to depths of 400 feet, though they can go deeper. They prefer to live in lairs in cavities or under boulders, and are particularly fond of kelp fields.

The shy and deadly blue-ringed octopus. SVSU

Blue-ringed octopus

The blue-ringed octopuses (in the genus Hapalochlaena) are four closely related species that live in tide pools in the western Pacific, particularly in Australia. They possess beautiful blue markings on their small bodies, which range from around five to 8 inches in length.

Though these animals are generally not aggressive and their bites are not particularly painful, they are one of the most dangerous creatures in the sea. That's because their venom is extremely potent, and has been known to kill people. Perhaps surprisingly, given this fact, they are found in many aquaria, in part because of their striking markings and their lack of ink.

Their poison has been identified as tetrodotoxin, which is also produced by dart frogs and pufferfish. It has also been theorized that this toxin creates zombie-like symptoms in humans, and may be responsible for the myth of zombies in the first place.

As with most venomous animals, as long as you don't step on them or pick them up, they won't hurt you, as they are not aggressive and feed on small crustaceans.

A dumbo octopus in the genus Grimpoteuthis. MBARI

Dumbo octopus

Just look at that little guy!

Dumbo octopuses are a group of cephalopods that have ear-like fins protruding from their head. They live in the deep sea, at depths of 9,800 to 13,000 feet. They are also called "umbrella octopuses" due to the shape of their mantle, or central body. There are 17 different species of these creatures discovered to date.

They measure about 8 inches to a foot in length, although the largest found reached 6 feet and weight 13 pounds.

They swallow their prey whole, unlike most other octopuses, which often tear off chunks. Their diet includes copepods, isopods, bristle worms and amphipods, according to the Aquarium of the Pacific.

Mimic octopus

The mimic octopus (Thaumoctopus mimicus) can impersonate both the appearance and behavior of animals such as lionfish, sea snakes, crabs, shrimp, flatfish and jellyfish. It does all these things to avoid predation. (Most of the creatures they mimic are poisonous, so it causes predators to steer clear of them.) It's still unclear exactly how the animals are able do this.

These animals grow to a length of 2 feet and were first discovered by scientists in the 1990s off the island of Sulawesi, Indonesia. The mimic octopus has also been spotted far away from there, in Australia's Great Barrier Reef.

Blanket octopus

The blanket octopus (Tremoctopus violaceus) is, even among the many other strange eight-legged beast out there, pretty weird. Males of this species are less than an inch long. But females? Females can reach 6 feet in length. To breed, the male sticks his specialized mating arm, or hectocotylus, inside the female and breaks it off. He then swims away, with only seven legs, and dies shortly thereafter. Ah, octopus romance.

The females basically look like huge blankets (hence the name), with flesh stretching between their legs. They often swim in the open water, which is rather unusual for octopuses (they generally stick to the sea bottom and crevices in which they can hide). When threatened, they can fan out their "blankets," a display that scares away predators.

This species is also immune to the venom of the Portuguese man o' war, a poisonous creature. For defense, the little males will break off a man o' war tentacle and wield it like a whip.

Coconut octopus

Forget humans—the coconut octopus, or veined octopus (Amphioctopus marginatus) can also stroll about on two legs, though they do it on the sea bottom. This may help them carry about objects on the ocean floor.

And that's useful, since these guys (as you might expect) are way into coconuts. Their shells, specifically. Australian scientists published a 2009 study showing that these creatures sometimes carry coconut shells far afield to create a defense fortress in which to live. It's a rare example of tool use in invertebrates, animals without backbones.

Octopus wolfi, the smallest octopode. Public domain

Octopus wolfi

This creature is the world's smallest octopus, at a length of less than an inch and weighing less than a gram. It is found in relatively shallow waters, between 10 and 100 feet, in the western Pacific.

Not much is known about these guys, although they have been described in the scientific literature since at least 1913. They are not the best for aquaria as they are somewhat likely to escape; one 2004 study gave them a 6 out of 10 rating on likelihood of escaping a tank.

Octopus wolfi is also pretty cute.

A male (left) and a female larger Pacific striped octopus mate. Roy L. Caldwell

Larger Pacific striped octopus

This attractive species can change color and patterns depending on its surroundings, going from dark brown to light colored with striking polka dots and stripes.

The larger Pacific striped octopus is also the most social octopus known to date. Most cephalopods aren't known to live in groups, but members of this species have been found in conglomerations of up to 40. Male and females also mate beak-to-beak, and, unlike in many other octopus species, the females don't eat males after copulation. Male-female pairs have even been seen cohabitating and eating together, which is unheard of in all other octopus species, says Roy Caldwell, a biologist at the University of California, Berkeley.

Larger Pacific striped octopuses are known for their beautiful stripes and polka dots, and they also appear to be more social than any other known species of octopus. Roy L. Caldwell

In addition, females of all other known octopus species rapidly begin to die once they brood. But these females live for months after they begin laying eggs, continuing to eat, hunt and mate. They also live for a year or two in captivity, longer than most tropical species.

They remain seldom studied, like many octopuses, because they live in the hard-to-investigate muddy waters off the coast of Nicaragua.

Russian President Vladimir Putin touches an octopus as he visits an oceanarium on the Russky Island in Vladivostok, September 6, 2012. REUTERS