The Rarest Ocean Animal and 6 Other Elusive Creatures That Mysteriously Lurk Below

Key points to remember about rare marine animals:

• The rarest marine animal is the vaquita – “little cow” in Spanish – which is a tiny porpoise found only in the Gulf of California in Mexico. It is also the most endangered marine animal in the world, with only 10 individuals left in the wild.
• Some of the rarest ocean animals can live in the unexplored depths of the ocean, including areas like the “midnight zone” where light from the surface cannot penetrate.
• The most mysterious sea animal could be several species, including the ghostly “Casper” octopus.

Despite everything we have learned about planet Earth, the ocean remains as vast and mysterious as ever. It spans about 70 percent of the planet but remains largely unexplored, and scientists estimate that more than 90 percent of marine species have yet to be classified.

Of those we know of, many are so elusive or imperiled that it is astronomically unlikely to encounter them in the wild.

When biologists talk about rarity, “we actually mean several different things,” says Craig McClain, who studies underwater life at Lafayette University. “Not all rare species are rare for the same reasons.”

Some have small but widespread populations, while others are abundant in a restricted geographic range or ecological niche. Some have probably always existed in small numbers, but McClain notes that many are rare “because humans made them that way through overfishing, habitat loss, or climate change.”

Here are seven of the ocean’s rarest inhabitants, creatures that remind us how far out of our reach the world remains and how fragile its wonders are.

Learn more: 5 endangered animals you should meet

What is the rarest marine animal?

The vaquita – “little cow” in Spanish – is a tiny porpoise found only in the Gulf of California in Mexico. It is also the most endangered marine animal in the world, with only 10 individuals left in the wild. Less than five feet long, with dark spots lining its eyes and mouth, the vaquita was not discovered until 1958. It is now listed by the International Union for Conservation of Nature (IUCN) as critically endangered, just one step above extinction.

The main cause of its decline, experts say, is bycatch: the creatures are trapped in gillnets set for totoaba, a species of fish prized for its swim bladder, a delicacy in Chinese cuisine. Despite international bans, illegal fishing persists and conservationists are now fighting to conserve the vaquita.

Learn more: The pygmy right whale was the oddity of the family and it never disappeared

1. Rare North Atlantic right whale

At the other end of the size spectrum, there’s another cetacean on the brink: the North Atlantic right whale. Commercial whalers, in search of blubber and oil, had already reduced their numbers significantly by the late 1800s. Today, there are approximately 360 individuals remaining, including 70 actively breeding females.

As they migrate along the eastern coast of the United States, these whales are still threatened by ship strikes and entanglements in fishing gear. They sometimes surface near busy ports, where collisions can be fatal. Scientists track the species by the unique patterns of rough skin on their heads, called calluses, and the results are grim: Since 2017, North Atlantic right whales have experienced an “unusual mortality event,” with more than 150 individuals dead, seriously injured or in poor health.

2. Kemp’s Ridley: the most endangered sea turtle

The smallest and most endangered of all sea turtles, the Kemp’s ridley turtle, nests along the Gulf Coast and Texas. Its synchronized mass nesting events – called arribadas, Spanish for “arrivals” – once attracted thousands of females to the shore. However, in the 1980s only a few hundred people came. Today, they are classified as critically endangered.

After a record high of just 702 nests in 1985, fishing regulations and protection of nesting beaches helped the population rebound by about 15 percent each year during the 1990s and 2000s. That said, oil spills and warming seas continue to pose a major threat to Kemp’s ridley turtles.

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3. Critically Endangered Chagos Brain Coral

Corals may seem less charismatic than marine mammals, but the Chagos brain coral is a fascinating piece of polyps. With its labyrinthine folds snaking across its dome-shaped surface, it bears an uncanny resemblance to its namesake. Moreover, it can live for centuries.

This remarkable coral, found only in the isolated Chagos Archipelago in the Indian Ocean, is also critically endangered. The main culprit is climate change: repeated marine heatwaves have bleached much of the coral, leaving survivors vulnerable to disease. On the bright side, since 2010 its habitat has been part of the Chagos Marine Protected Area, which encompasses the largest coral atoll in the world.

4. Goblin shark: a rare living fossil

Until now, all animals have been pushed to the brink of extinction by human activity, in one way or another. But some ocean creatures are naturally vulnerable due to their vulnerable state. In fact, McClain says, in deep water, “scarcity is actually the norm.” Thousands of feet below the surface, scarcity of food and suitable habitat ensure that most populations remain small and scattered.

The goblin shark falls into this category. With pink, translucent skin, a ridiculously long, pointed snout, and a protruding jaw that thrusts forward in a flash to capture prey, the goblin shark resembles a hideous movie monster. As the only remaining species within the ancient family Mitsukurinidae, it is often referred to as a “living fossil”. These sharks patrol continental slopes more than 4,000 feet deep, hunting not by sight but by sound, smell and electric fields produced by other animals.

Learn more: These 12 deep-sea creatures are more comical than scary

5. Giant ghost jellyfish: a rare ocean sighting

Measuring over 30 feet long, the giant ghost jellyfish is one of the largest invertebrates in the ocean. Yet despite its size, it is also one of the most rarely seen species. Since biologists first described this jellyfish in 1910, it has only been observed alive about 100 times.

With an inflated, dome-shaped bell more than 3 feet in diameter and ribbony arms that trail behind it as it drifts in the depths, the ghost jellyfish truly deserves its spectral name. It is usually found in the “midnight” zone, up to 22,000 feet deep, where light never penetrates.

6. The most mysterious sea animal

That title could go to a number of deep-sea species, whose behaviors and lifestyles are virtually unknown to science – giants like the giant squid, the anglerfish with their bioluminescent lures, and the tube-shaped siphonophores, colonial creatures that can grow longer than a blue whale.

But as deep-sea expeditions become more common, scientists continue to discover entirely new species. One of them, first spotted in 2016, is the “Casper” octopus, a pale, ghostly creature found on the seafloor near Hawaii, more than two miles underwater. Its dull skin amazed experts, because octopuses are usually brightly colored, even those that live in a light-free environment.

“It could be that they are quite common,” Janet Voight, associate curator of invertebrate zoology at the Field Museum of Natural History in Chicago, told the BBC. “It’s just an indicator of how little we know about what’s going on there.”

Learn more: 99.999 percent of the ocean’s depths are unexplored — its secrets are essential to understanding our planet

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