10 of the Largest Living Creatures in the Sea

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10. Japanese Spider Crab | Leg span: 12.14 feet (3.7 m)

credit: Wikimedia Commons

Meet the incredible creatures that have inspired legends of sea monsters throughout the ages. The largest living things in the world call the sea their home, and in fact, the largest creature to have ever lived on the planet currently resides in the ocean now. Many of these giant creatures have been at the heart of sea monster lore over the ages – and while they are not actually monsters, they are tremendous in size and some remain elusive and wildly mysterious. That's what happens when you live in a place as unexplored as the ocean is. We currently know of 228,450 marine species worldwide – there is up to 2 million more multi-celled marine organisms that remain unknown. While the ocean's leviathans get a lot of scientific attention, there is no shortage of lore still in the works in popular culture, especially when it comes to size. To set the record straight, a group of researchers embarked on a comprehensive survey of past studies and verifiable documentation to get accurate measures for the largest known marine species. Here's what they found.

At over 12 feet in width the Japanese spider crab has nothing on the 120-foot giant who is the longest in the sea (see page 10) ... but this is a crab. It is an arthropod, it is from the same phylum that includes crustaceans, spiders and insects. And it is not only the largest crab or crustacean in the family, but it also holds the title for the largest arthropod of all. Given that there are some 5 to 10 million species of arthropods on the planet, being king of the realm is pretty impressive.

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9. Ocean Sunfish | Total length 10.82 feet (3.3 meters)

credit: Per-Ola Norman

Also known as a mola mola, the wonderfully weird ocean sunfish is the heaviest of all bony fish. Affectionately called a "swimming head," the giant fish without a tail has been measured at 10.82 feet and an astonishing 5070 pounds. And if you're wondering how a fish without a tail swims, it powers itself by its mighty fins.

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8. Oarfish / Total length: 26.25 feet (8 meters)

credit: Wikimedia Commons

Is it any wonder that the decidedly odd oarfish is often referred to as a sea serpent or dragon? These guys are long – the longest bony fish that we know of – and live at depths of 3,300 feet. They are rarely seen alive, most of our knowledge of them comes from specimens that have washed ashore. The top photograph made the hoax rounds when it was said to show U.S. servicemen in Laos during the Vietnam War with a captured "Mekong Dragon." In reality, the photograph was taken in 1996 and shows a giant oarfish found on the shore of the Pacific Ocean near San Diego, California. This guy was 23 feet (7.0 meters) long and weighed 300 pounds (140 kilograms). The image on the bottom comes from Harper's Weekly and was part of a series entitled, Monsters of the Sea. The illustration depicts an oarfish that washed ashore in Bermuda beach in 1860. The 16-foot long fish was originally described as a sea serpent.

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7. Giant Pacific Octopus | Radial spread: 32.15 feet (9.8 meters)

credit: Damn_unique/Flickr

Even though octopuses are my favorite animal on the planet (beside my cat ... oh, and my kids), I'm not so sure how I'd feel about being in the wild and coming across one that was 32-feet wide. That is a big octopus – and in fact, the aptly named giant Pacific octopus is the biggest cephalopod of all. Octopuses are so weird, so wonderful, and so smart – they can open jars, mimic their brethren, solve mazes, and play with toys. I've written about them a lot around here, but I always learn more. For instance, although I knew their arms were smart, how about this?

Two-thirds of an octopus’ neurons reside in its arms, not its head. As a result, the arms can problem solve how to open a shellfish while their owners are busy doing something else, like checking out a cave for more edible goodies. The arms can even react after they’ve been completely severed. In one experiment, severed arms jerked away in pain when researchers pinched them.

PS: I meant it when I wrote "octopuses." As

explains, the word “octopus” comes from the Greek, októpus, meaning “eight foot.” The word’s Greek roots means it’s pluralized as a Greek word, too, which depends on both a noun’s gender and the last letter it ends with. In this case, an -es is simply tacked on. So no octopi, octopodes or octopussies.

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6. Giant Squid | Length: 39.37 feet (12 meters)

credit: Christopher Cacho/Flickr

Taking the prize for longest cephalopod, the sea monster Kraken! The incredibly elusive giant squid has not been studied very extensively given how little observation scientists have had, but that doesn't mean that it hasn't become legendary in the realm of sea monster tales. However, there is some incredible footage of one taken by a research vessel off the coast of Japan.

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5. Basking Shark | Total length: 40.25 feet (12.27 meters)

credit: Chris Gotschalk

The basking shark is the second largest fish in the modern ocean, that we know of at least. The biggest one on record measured in at over 40 feet. That is longer than a school bus. And even better, they can weigh up to 8,000 pounds. But not to worry should you come across one while taking a dip in the depths; they are gentle giants with a diet of mostly plankton, fish eggs, and larvae.

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4. Whale Shark | Total length: 61.68 feet (18.8 meters)

credit: Crystaldive

Meet the largest fish in the sea, the beautiful whale shark. These majestic giants roam the oceans across the planet, looking for plankton and doing other things that fish do – sometimes even playing with people who love to swim with them. More whale than shark, these fish are listed as vulnerable, though they are still hunted in some parts of the world.

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3. Sperm Whale | Total length: 78.74 feet (24 meters)

credit: Gabriel Barathieu

At almost 80 feet in length, the beautiful sperm whale happens to be the largest of the toothed whales and the largest toothed predator of all. If you were to place it on its end and put it on the street, it would be as tall as an 8-story building. Its clicking call can be as loud as 230 decibels underwater, equivalent to 170 decibels on land, about the loudness of a rifle shot within a few feet of one's ear. It has the largest brain of any animal on the planet, more than five times heavier than ours. Unfortunately for the sperm whale, they were fiercely hunted in the 18th, 19th and 20th centuries; whalers sought the spermaceti which was used for candles, soap, cosmetics, lamp oil and many other commercial applications. Before whaling there was an estimated 1.1 million of them, now only several hundred thousand – which may be a lot compared to other whales in peril, but still disheartening given their once abundant population.

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2. Blue Whale | Total length: 108.27 feet (33 meters)

credit: Ocean Institute

Most of us have seen photos of a glorious, gigantic blue whale. But without something to show their scale, it's hard to tell just how extraordinarily enormous they are. Hence, the illustration above. They. Are. Huge. In fact, the blue whale is the largest animal ever known to have existed – even out-sizing dinosaurs. They weigh up to 441,000 pounds. Their hearts are the size of a car; its beat can be detected from two miles away. At birth they already rank amongst the largest full-grown animals. I'm sure you're getting the picture. Because of commercial whaling the species almost went extinct by the 20th century, but thankfully has slowly recovered following the global whaling ban. That said, they remain endangered and face a number of serious threats including ship strikes and the impacts of climate change.

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1. Lion’s Mane Jellyfish

credit: Alan Weir/Flickr

Lion’s Mane Jellyfish: 120 feet (36.6 meters)

While the blue whale is the overall-largest king of the sea, the lion's mane jellyfish goes to the top of the list for being the longest. And as the longest medusozoa of all, these languid beauties have tentacles that reach an astonishing 120 feet in length. It's hard to know why they are graced with such extraordinary appendages. They are said to get tangled in marine debris or with other tentacles, and as they take notably more time to contract, they are more vulnerable to to predators with a taste for jellyfish arms. Regardless, they don't seem to mind – and if nothing else, it's earned them a place of distinction with us humans ... for whatever that's worth. (Not much, but still.) • • •