Ten Bizarre Creatures from Beneath the Waves

Our oceans and seas are a hotbed of weird and wonderful nature, home to some of the most remarkable species known to science. In these extreme ecosystems, bizarre creatures thrive and perform feats that scientists once thought were impossible.

In this list, we plunge beneath the waves to explore some of the most surprising life forms that the marine world has to offer. We’ll take in worms that eat skeletons, catfish that can climb waterfalls, and steamy leopard shark trysts. From tiny dolphins to toxic blue dragons, here are ten of the strangest aquatic species from across the globe.

Related: 10 Incredibly Unsettling Things We Still Don’t Know about the Ocean

10 World’s Smallest Dolphin

The smallest marine dolphins known to science are Hector’s dolphins—tiny divers with a knack for dazzling acrobatics. They grow to around 4.5 feet (1.4 meters) long and can be found racing through the waters off New Zealand. Those near the North Island fall under the critically endangered Māui subspecies, while their cousins are known as South Island Hector’s dolphins.

Hector’s dolphins can dive to impressive depths for their small size. The petite swimmers plunge to around 400 feet (120 meters), flipping and rolling like acrobats as they descend. In a 2025 study, University of Auckland researchers fitted 11 South Island Hector’s dolphins with tracking tags and were stunned by their range. One swam 9.3 miles (15 kilometers) along the coast.

At shallower depths, the dolphins drift slowly to snatch cod and flatfish. Midway up, they plow through the water, snapping at schools of smaller fish as they go.^[1]

9 Leopard Shark Tryst

In 2024, marine biologists discovered just how steamy shark courtship can get. In a world first, Australian scientist Hugo Lassauce filmed three leopard sharks mating together on the seabed.

Researchers know very little about how these freckled fish reproduce in the wild, as most studies have focused on captive specimens. The new footage, captured near New Caledonia in the South Pacific, was the first time leopard sharks had been caught on camera mating in their natural habitat. Lassauce came across two males engaging with a female during a dive and filmed the trio for 90 minutes.

The encounter wasn’t exactly romantic for the female—both males bit her pectoral fins and held on while she struggled to break free. When it was over, the males lay exhausted on the seabed while the female swam off.

Leopard sharks (Stegostoma tigrinum) are endangered, and scientists hope that new insights into their reproductive behavior could help conservation efforts. Lassauce plans to continue studying how the species breeds and raises its young in the wild.^[2]

8 Elusive Blue Dragons

The oceans are home to some of nature’s most surreal creatures, including the stunning blue dragon—Glaucus atlanticus. These dazzling sea slugs drift on their backs through tropical and temperate waters, floating wherever the currents take them.

Their iridescent coloring isn’t just for show. The blue and silver hues camouflage them against the waves, hiding them from predators both above and below. Blue dragons feed on other surface-dwelling marine creatures, such as by-the-wind sailors and violet snails, but their favorite prey is the Portuguese man o’ war. They consume the man o’ war’s tentacles and store its stinging cells inside their own tissues, ready to unleash them if threatened.

Blue dragons are weak swimmers and often wash ashore when winds and tides shift. In 2024, several washed up on Texas beaches. Despite their beauty, experts warn beachgoers not to touch them—their borrowed toxins can cause painful stings or even more severe reactions.^[3]

7 Gravity-Defying Catfish

In 2024, officials in Rochedo, Brazil, made a remarkable discovery. They witnessed thousands of bumblebee catfish scaling the slippery rock face of a waterfall in the Aquidauana River. Normally, these orange-and-black striped fish dwell at the bottom of fast-moving streams—but come nightfall, they begin climbing.

Scientists were baffled. How could fish ascend a vertical waterfall? By analyzing their movements, researchers found that the catfish use specialized fin placements and suction-like pressure bubbles to cling to the rocks. They believe the tiny climbers make the ascent to reach narrow upstream channels where they breed.

Whatever their motive, these miniature mountaineers proved that nature always finds a way.^[4]

6 Ancient Bone-Munching Worms

On the ocean floor, some worms live up to a grim reputation. For more than 100 million years, bone-eating worms have feasted on the remains of fallen sea creatures.

When large animals die and sink, scavengers strip away the flesh, leaving the skeletons to become food for vast colonies of bone-eating worms. These deep-sea dwellers, known as Osedax, burrow into bones and absorb fats and proteins with the help of symbiotic bacteria.

Modern Osedax worms are found on the carcasses of whales and other large animals. Fossil evidence shows that their ancestors once consumed the bones of massive marine reptiles such as plesiosaurs and ichthyosaurs. They have no mouth or digestive tract, making their unique method of feeding one of evolution’s most bizarre adaptations.^[5]

5 Squishy-Headed Barreleye Fish

Deep in the northern Pacific Ocean swims one of nature’s strangest-looking fish. With green, tubular eyes and a transparent head, the barreleye looks like something out of a science-fiction movie.

Scientists rarely see these shy, slow-moving fish. Their dome-shaped heads are filled with a clear fluid that cushions and protects their upward-facing eyes. Barreleyes typically hover in near-darkness, gazing upward to spot silhouettes of potential prey. Once they locate food—tiny crustaceans or zooplankton—they can rotate their eyes forward to track and intercept it.

Researchers believe Macropinna microstoma often steals its meals from siphonophores and other gelatinous creatures drifting in the deep.^[6]

4 Giant Marine Viruses

When people imagine underwater threats, sharks and octopuses usually come to mind. But lurking in the Pacific are other monsters—giant viruses that dwarf most known pathogens. Some carry thousands of genes and boast complex tails more reminiscent of alien machinery than biology.

One standout is PelV-1, discovered in 2024. Most viruses with tails are tiny, but PelV-1 has a main shell about 200 nanometers wide and an extraordinary tail stretching 2.3 micrometers—the longest known in the viral world. For comparison, that’s roughly 19 times longer than an entire coronavirus particle.

Scientists think PelV-1’s tail helps it penetrate host cells and infect plankton. Once inside, the tail disintegrates, leaving behind a viral factory ready to replicate. Even at the microscopic scale, the ocean has its share of monsters.^[7]

3 Supergiant Amphipods

At the bottom of the ocean lives a shrimp-like giant roughly the size of a loaf of bread. These ghostly crustaceans, called supergiant amphipods, are among the largest members of their kind.

Alicella gigantea belongs to a family of over 10,000 amphipod species, but none come close to its size. Measuring up to 13 inches (34 centimeters) long, it was first recorded in the 1970s in the North Pacific Ocean. For decades, scientists assumed it was rare, but a 2025 study proved otherwise.

By analyzing DNA data and decades of records, researchers found that these pale behemoths might inhabit up to 59% of the world’s oceans—including all six major ocean basins. Far from being elusive, A. gigantea may be one of the deep sea’s quiet success stories.^[8]

2 Portuguese Man o’ War

The Portuguese man o’ war is one of the ocean’s strangest organisms—and it’s not even a single creature. What appears to be one jellyfish-like body is actually a colony of specialized clones called zooids, all working together as one.

This arrangement is known as a siphonophore. Each zooid performs a specific task: one keeps the colony afloat, while others handle hunting, digestion, and reproduction.

The Portuguese man o’ war (Physalia physalis) gets its name from its resemblance to an 18th-century warship. Its blue, violet, or pink float drifts on the surface while tentacles trail below, often stretching 30 feet (10 meters). These tentacles are lined with venomous stinging cells powerful enough to paralyze small fish and other prey—and painful enough to leave humans in agony.^[9]

1 Gorgeous Glass Octopus

Few marine species are as mesmerizing as the glass octopus. This nearly transparent cephalopod reveals its inner workings—eyes, optic nerves, and even its digestive tract—through a ghostly clear body.

Only a handful of people have ever seen Vitreledonella richardi in the wild. These ten-tacled wonders glide through tropical waters roughly 3,000 feet (900 meters) below the surface and grow to about 1.5 feet (0.5 meters) long.

Much of what we know about glass octopuses comes from specimens found inside predators’ stomachs. But in 2017, scientists from the Schmidt Ocean Institute captured rare video footage of two living individuals during a deep-sea expedition in the Pacific—offering an enchanting glimpse into one of nature’s most mysterious creatures.^[10]