There are many strange and wonderful creatures in the great blue ocean, but few hold our attention like the octopus. Perhaps octopuses are so engaging because they're highly intelligent, and it's always a thrill to meet another creature that is so intellectually advanced — especially when they take such a dramatically different physical shape. Even within this distinct group of animals there is wild variability in appearance and behaviors. These eight species underscore the variety of beauty and strangeness in the Octopoda order.

1. Coconut Octopus

The coconut octopus (Amphioctopus marginatus) uses of coconuts and shells for hiding. Sascha Janson/Shutterstock

This species is named for a peculiar behavior. The species dwells in the tropical Pacific ocean, which is edged with coconut tree-lined beaches. The coconut octopus has figured out how to gather coconut shells and other seashells and use them for shelter. It will even carry its found shells from place to place, holding them with six arms while walking across the ocean floor on two legs.

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The bipedal locomotion is eye-catching, but it's also mind-boggling: Some researchers claim that by using shells for shelter and defense, this octopus species is engaging in tool use. While the notion of tool use isn't universally accepted, it sure seems like the octopus has a planned purpose for those coconut shells and puts plenty of effort into hobbling across the sand with them.

2. Giant Pacific Octopus

The North Pacific giant octopus is one of the behemoths of the cephalopod world. Naoto Shinkai/Shutterstock

This is perhaps one of the most well-known and well-loved species of octopus. It's the largest species in the world, weighing in at as much as 150 pounds and measuring 15 feet long. It's also known for its ability to change color, a skill shared by many cephalopods, though the giant Pacific octopus (also known as the North Pacific giant octopus) does it with particular flair. They use the ability to blend in with their surroundings, becoming practically invisible. They also use it to express mood. Found anywhere from tide pools to 6,600 feet below the ocean surface, the species looks for a huge range of crustacean prey, from shrimp to lobsters, and will also catch and feast upon fish and other octopuses.

3. Dumbo Octopus

Just listen to the voices of the researchers as they come across this octopus while surveying the deep, and you'll know why this species is on the list. "The world loves a dumbo," as one voice puts it. The dumbo octopus is actually a name for a group of deep-sea umbrella octopuses, all of which have the characteristic fins that look like the ears of "Dumbo" the elephant. They have been found at depths reaching 13,100 feet, which makes them the deepest-dwelling of all octopus species. While most species are quite small, the largest of the dumbo octopuses measures at 5 feet 10 inches and weighs 13 pounds. Unlike other octopus species, dumbo octopuses don't have ink sacks, presumably because they don't encounter as many predators at such otherworldly depths.

4. Blue-Ringed Octopus

The blue-ringed octopus is beautiful to look at, but don't touch!. SChantra/Shutterstock

This is certainly one of the most beautiful of octopus species, with vivid blue rings that make you want to reach out and touch the little eight-armed miracles. But don't. Seriously, don't. Those blue rings — much like the red marks on a poison dart frog or black widow spider, signify danger. They are a glaring "Don't even think about it" warning.

As Ocean Conservancy tells us, "Although all octopuses (as well as cuttlefish and some squid) are venomous, the blue-ringed octopus is in a league of its own. Its venom is 1,000 times more powerful than cyanide, and this golf-ball sized powerhouse packs enough venom to kill 26 humans within minutes. It's no surprise that it's recognized as one of the most dangerous animals in the ocean."

There are four species of blue-ringed octopuses and all are unbelievably deadly. However, they're also unaggressive. Hanging out doing its own thing in shallow tide pools and reefs of the Pacific and Indian oceans, it typically only bites when it feels threatened. So as long as you don't accidentally squish it or (stupidly) try to handle it, you should be perfectly safe sharing the water with it.

5. Atlantic Pygmy Octopus

Most species with "pygmy" in the name are adorable, and that's certainly true of this octopus species. The Atlantic pygmy octopus grows to no more than about 5.5 inches in length.

"They are very playful and seem to be extremely intelligent," writes OctopusWorld. "They can problem solve to make their environment one that fits well for their needs."

This includes using shells and other objects as hiding places, and pulling sand over the top for expert camouflage. It likes crustaceans for more than just the shelter — it also likes to eat them. Using a sharp radula, it drills a hole into the shell, spits poisonous saliva inside to paralyze its victim, then proceeds to snack. A little gruesome for a creature so cute, but it's a tough life in the ocean.

6. Mimic Octopus

The mimic octopus adjusts its tentacles to take on the shape of other sea animals. orlandin/Shutterstock

This is perhaps the most mind-boggling of octopus species thanks to its incredible skill at impersonating other sea creatures. One octopus can figure out how to mimic as many as 15 other species in its surroundings — the only species in the ocean known to mimic such a large number of other animals.

It pulls out all the stops as it gets into character. National Geographic points out, "Like other mimics, the octopus changes its coloring to disguise itself. More unusually, it can also contort its body to take on the appearance and behavior of several animals, including the lionfish, jellyfish, sea snake, a shrimp, a crab, and others."

Not only will it mimic animals like the lionfish to evade potential predators, but it will mimic animals in its own predatory efforts. For example, it can mimic a crab and approach a potential "mate" only to eat the unlucky dupe.

7. Caribbean Reef Octopus

The Caribbean reef octopus is a beautifully colored resident of tropical waters. John A. Anderson/Shutterstock

The Caribbean reef octopus can rapidly change its colors, patterns and even its skin texture to blend in perfectly with its surroundings as it moves around the coral reef. Several species of octopus are skilled at camouflage, but this species is considered one of the masters, matching its background even if it's resting on a multicolored surface. Oceana writes, "A camouflaged Caribbean reef octopus can be nearly impossible to see."

It needs such a high level of camouflage ability because it's the prey for large bony fish and sharks that live in reefs. Strictly nocturnal, it hunts fish and crustaceans under the cover of darkness.

8. Seven-Arm Octopus

Last but not least is the seven-arm octopus, which despite its name, does have eight arms. The misnomer comes from the fact that in males, the specially modified arm that is used for egg fertilization is held in a sac beneath one of its eyes. This makes it look like there are seven arms. Females, on the other hand, have eight obvious arms. This species nearly matches the Pacific giant octopus in size, reaching lengths of 12 feet and a hefty 165 pounds. Despite its large size, it isn't very well known. Being a species that lives in the deep, it has only been spotted a handful of times by researchers using submersibles. But the last time (and only the third time) it was spotted by researchers it was eating a jellyfish, a surprising meal for an octopus and an important bit of information about how this species makes its living.