Buzz
The ocean is home to an array of strange, extraterrestrial-like beings. Even creatures that are already bizarre, like jellyfish and sea slugs, can become even more extraordinary when they adapt to specific ecological environments.
10. Benthic Ctenophores
You may recognize Ctenophores, commonly known as “comb jellies,” which are transparent invertebrates that use their delicate, rippling cilia to propel themselves through the water. However, some species lack these cilia and instead move slowly across the ocean floor, with their mouths facing downward.
With two large, branching horns, they resemble a combination of a slug and a pair of bunny ears, each horn capable of extending a long, silky feeding tentacle into the water. Other smaller species are transparent and expertly camouflaged, while some spend their whole lives attached to starfish.
9. Hooded Nudibranchs
The hooded or “lion” nudibranchs from the genus Melibe are like the Venus flytraps of the sea slug world, with their large mouths opening into nets lined with tooth-like, sticky tentacles.
Attached to seaweed, their transparent bodies are nearly invisible to tiny fish and shrimp that might accidentally swim into their trap. Oddly enough, these slugs are also said to smell like flowers when taken out of the water.
8. Helmet Jellyfish
Unlike the typical jellyfish that trails long, threadlike stinging tentacles behind its swimming bell, the helmet jellyfish, Periphylla periphylla, has thicker, more rigid tentacles that it extends in front of it while swimming. These tentacles capture small fish and pull them into its digestive cavity.
Preferring darkness, they typically reside as deep as 1,000 meters (3,000 ft) below the ocean's surface. However, large groups of them may surface at night, and they have even been known to become invasive pests in certain coastal areas. Their dark red to purple hue is believed to make the jellyfish nearly invisible to most predators, even after consuming bioluminescent prey.
7. Xyloplax
The last thing you would imagine a starfish feeding on is wood, yet that’s exactly what happens with Xyloplax. Known as “sea daisies,” Xyloplax are small, saucer-shaped starfish relatives, adorned with feathery spines that resemble cartoonish flower petals. These creatures are found deep in the dark abyssal zones of the sea.
It's a particularly odd habitat for an organism that feeds solely on wood, much like a termite. However, it's not surprising that vast amounts of wood—from broken twigs to entire dead trees—find their way into the ocean daily, with much of it sinking to the ocean’s depths.
6. Pterotrachea
What looks like a transparent, beady-eyed sausage with a trunk on its head? It’s another strange species of gastropod, often referred to as a “sea elephant,” a swimming snail with a diminutive, internal shell.
Unlike most snails, Pterotrachea is an agile, visual predator. Its remarkable, telescope-like eyes enable it to detect even the smallest prey in the surrounding water, which it then slurps up with its trunk. If it appears upside-down, that’s because it is. Sea elephants swim on their backs, likely using this position to surprise their prey from below.
5. Ramisyllis Multicaudata
While it’s a tough contender, the marine worm R. Multicaudata might just boast one of the most peculiar body structures in the animal kingdom. Much like a twist on the myth of the hydra, it has a single head but an apparently endless number of twisting, branched bodies resembling a web of segmented, hairy roots.
The head is located at the center of a sea sponge, while its many bodies extend throughout the sponge’s holes and tunnels. Whether this relationship is parasitic or mutually advantageous remains unclear, but both organisms may provide some form of protection to each other.
4. Dolphin Barnacles
Typically filter-feeding, immobile crustaceans, most barnacles are suited to grow on stationary rocks or on large, slow-moving animals like whales and turtles. However, one species can be found clinging to the fins of fast-swimming dolphins.
Their long, slimy, leech-like bodies trail behind the dolphin as it leaps and dives through the water, with a deeply embedded, barbed anchoring organ in the sea mammal’s flesh. Like most barnacles, it feeds on plankton in the surrounding water, but it attaches to a dolphin primarily for its own safety. After all, there aren’t many predators that target barnacles and are capable of catching a healthy porpoise.
3. Christmas Tree Worms
These creatures will seem familiar to anyone who has seen James Cameron’s Avatar, which drew inspiration from them almost exactly for its alien forest fauna.
These filter-feeding worms spend their entire adult lives sealed within a single tubular tunnel, carved out of rock or coral. The “Christmas trees” visible are actually the creatures' intricate, coiled palps, complex lips used to trap plankton. These appendages also serve as gills. Even more bizarre, they have specialized light-sensitive cells that enable the worms to see. So adapted to exposing only their mouths, the worms' mouths have evolved into their eyes.
2. Ribbon Worms
Ribbon or Nemertean worms are among the most bizarre animals you’ve probably never heard of, despite being found not only across the ocean but even in your own backyard—albeit typically much smaller.
Almost all of these slimy, gooey creatures are carnivores. They scavenge dead animals or capture live prey, overpowering it with a venomous sting, acidic saliva, or toxic slime secretion. Many feature a projectile proboscis that can even branch out like a spider’s web, while others can simply stretch their mouths open like pythons, swallowing prey far larger than themselves. Some species are among the longest animals known, reaching lengths of nearly 60 meters (200 ft) when fully extended, though fortunately still only as wide as a human finger.
1. Stalked Jellyfish
We’ve already encountered one jellyfish that swapped swimming for crawling, but that was a comb jelly. The Stauromedusae are true jellyfish that have given up swimming in favor of a lifestyle more akin to their distant cousins, the corals and anemones.
What would normally be the top of the jellyfish's bell is now a stalk, flexible and ending in a powerful sucker, enabling the funnel-shaped creature to cling to rocks or seaweed while waving its open mouth in the water. This strategy has also been observed in a slug. The stinging tentacles are grouped into eight pom-poms at the ends of short, muscular arms, which the animal uses to seize and hold helpless prey. When it wants to move, it can walk end over end, flipping from its sucker-tipped stem to its pom-pom arms, or it can detach and drift in the water, letting the current carry it to new feeding grounds.
