Creatures of the Deep: 5 Incredible Underwater Species

Discover five incredible underwater species whose abilities will astonish you.

Mar 17, 2023By Donna Hobson
incredible deep underwater species

When you consider that oceans cover 70% of the Earth, it's pretty astonishing how little we know about what lies beneath the surface. Researchers in Nova Scotia suggest that up to 91% of marine animals are still unknown to us, and those creatures that have been discovered often prove that science is stranger than fiction.

Discover five of the most incredible underwater species whose unique appearance and abilities fascinate scientists worldwide. From the immortal jellyfish to the intestine-ejecting sea cucumber, here are some surprising facts about these creatures of the deep.

5. Sea Cucumber

sea cucumber
Image Source: Secrets of self-defense revealed in sea cucumbers •

Sea cucumbers are echinoderms with leathery skin that live in the ocean. They eat algae and aquatic invertebrates from the ocean floor by sucking them up through tube-like feet around their mouths. These invertebrates resemble a cucumber with a mouth at one end and an anus at the other; they use their anus for breathing, and some fish can even use the sea cucumber's anus as a place to seek refuge!

The average size of a sea cucumber is between 3 and 12 inches, but they can grow to lengths of six-and-a-half feet. They can live for up to 10 years, surviving through two main lines of defense: if a predator approaches, the cucumber can shoot out sticky threads to entangle them. Or, in a slightly more bizarre move, they can expel their internal organs and regenerate them later via a process called evisceration.

4. Immortal Jellyfish

immortal jellyfish
Image Source: 10 Incredible Immortal Jellyfish Facts - AZ Animals (

Living forever is impossible, right? Not if you're an immortal jellyfish, which has the ability to convert its cells backward, allowing it to become younger. The process is known as trans differentiation and involves the species converting one type of cell into another. These impressive sea creatures have been found all around Japan and the Mediterranean, but thanks to their immortality and ocean currents, their population could be in the millions.

This bell-shaped jellyfish is a tiny 4-5mm tall and wide in size but can possess up to 90 tentacles. Still, this jellyfish is not indestructible - it can still die if a predator decides to gobble it up for an afternoon snack. Not only does this creature have the longest lifespan on Earth, but they've been floating through the oceans for millions of years, existing long before the dinosaurs - pretty impressive.

3. Tardigrade

tardigrade water bear
Image Source: Tiny but tough: the tardigrades | Zoology | The Guardian

When it comes to extreme animals, the tardigrade has to take the title of the most resilient, as it can survive in places that many other organisms cannot. Also known as "water bears," these hardy little creatures are found everywhere on our planet (and the moon, but we'll to that later), from the tops of mountains to the deepest points in the ocean.

Tardigrades need water to do pretty much anything, including eating or reproducing, but they have evolved with incredible skills that allow them to overcome the issue of drought. If a tardigrade's environment dries up, so do they; they enter a state called desiccation, during which they lose all but 3% of their body's water and slow their metabolism to just 0.01% of its regular speed.

This metabolic state - called cryptobiosis - means these creatures can survive for over 30 years without eating. Some scientists even suggest the tardigrade could survive in this shriveled state for a century before "coming back to life." And these amazing skills allow them to survive some of the harshest conditions in the world; a tardigrade can tolerate pressure more than five times greater than the deepest part of the oceans and temperatures that reach almost absolute zero.

Back to the moon - in 2019, an Israeli spacecraft crashed into the moon, spilling thousands of these creatures onto its surface; thanks to their resilient nature, there's every chance they'll survive for decades until they're re-exposed to water. Could a lack of oxygen and intense space radiation present a problem? Not for this other-worldly creature who can also tolerate the conditions of outer space far better than any Earthly being would expect.

2. Japanese Spider Crab

japanese spider crab

The Japanese Spider Crab is the largest known crab in existence; once they reach adulthood, the carapace (main body) stays the same size, but the legs keep growing. The body can reach a total length of 30cm, but the legs can span an incredible 12 feet across. The term spider most likely refers to its spindly legs, as these invertebrates have a total of 10 legs themselves.

A female Japanese Spider Crab can lay as many as 1.5 million eggs in a single season; still, only a few of these will reach adulthood and migrate to deeper ocean waters. Those lucky enough to reach maturity have few natural predators in the deep depths (160 - 2000 feet) of the ocean; they also possess a thorny exoskeleton for added protection.

They may look fearsome, but the Spider Crab is a scavenger rather than an active hunter, and they prefer to look for plants or dead animals lingering on the ocean floor. These crabs also like to scavenge for sponges and plants with which they can decorate their shells in a process that helps them camouflage with their environment.

1. Dumbo Octopus

dumbo octopus

The Dumbo Octopus may well be the cutest creature in the sea with its bulbous head and doe eyes. Still, don't underestimate the resilience of this underwater predator; it takes the title for the deepest-living genus of all octopuses, living at least 4,000 meters below the water's surface. In addition, these creatures can grow to impressive sizes - the largest on record was 5 ft 10 in and weighed 5.9kg.

But the average size among the 14 species is between 20 and 30 cm. These cute creatures are part of a group known as "umbrella octopuses" because they have an interconnecting web of skin between their arms, allowing them to use their bodies like an umbrella to move across the ocean floor.

Donna Hobson
By Donna Hobson

Donna believes that keeping a pet is the key to a happy life. Over the years, many creatures have passed through her home - Sooty the cat, Millie the rabbit, Stuart (Little) the guinea pig, and Trixie the tortoise, alongside her pet goldfish, Zippy, who lived to the grand old age of 24 years! She currently resides with her black kitten Jinx and an aquarium full of fish and snails to entrance them both. When she is not looking after her pets, Donna enjoys researching and writing the answers to all your pet-related wonders.