Creepy photos reveal the microscopic world of fascinating creatures that thrive on sandy beaches wor

• Sand is host to hundreds of microscopic species that are yet to be discovered.
• Deep sea biologist Holly Bik is on a quest to discover as many of these species as possible.
• These species are called nematodes, and they're a vital key to ecosystems worldwide.

You probably see all kinds of critters on the beach — but what you might not realize is that the sand beneath your feet is home to a thriving microscopic universe of roundworms called nematodes.

Nematodes are typically less than 1 millimeter long and live in every corner of the world, from ocean trenches and snowy tundras to scorching deserts and volcanic soils.

They're nature's decomposers, recycling nutrients back into their environments.

Deep sea biologist Holly Bik said it's estimated there are millions of different species of nematodes, but biologists have described fewer than 5,000 marine species to date.

On their quest to discover new species worldwide, Bik and her team have collected samples in such varied destinations as East Antarctica and the north slope of Alaska to Tybee Island, Georgia, and La Jolla, California.

Nematodes are typically less than 1 millimeter in length, so Bik and her team use powerful microscopes to study them. This particular species — known as the Ceramonema — is commonly found on underwater mountains in the deep sea.

What sets these nematodes apart are the complex wave-like patterned plates covering their entire body.

"There are so few scientists working on these species and there's so much sand out there," Bik said. "If you grab a bit of sand outside your doorstep or at your local beach, you're probably holding hundreds of new species."

This nematode — the Xyala — is one of the most abundant species on sandy beaches worldwide.

Its defining features include rows of raised ridges encircling its body, a small circular sensory pore, and sensory "hairs" around the head. 

While deep sea habitats cover much of the earth's surface, our current understanding of deep-sea nematodes species is based on sampling from an area less than half the size of a tennis court, Bik said.

The presence of Odontophora nematodes are a sign of a clean, unpolluted habitat and often make sandy beaches their home.

Scientists believe these worms use the spiral-shaped, gel-filled pore on their bodies to sense bacterial metabolites in their environment and locate prey. 

Desmodorid nematodes, like this one, can be found in marine mud and sand worldwide — and are especially common in seafloor habitats with low oxygen.

This species is characterized by the short setae, or sensory hair-like organs, covering almost its entire body.

In some cases, Bik's team uses DNA sequencing to help identify the species of nematode, if they don't always have distinctive, defining features at first glance. 

Enoploides nematodes are fierce predators thanks to their three extendable y-shaped jaws — each of which features its own large tooth.

They enjoy feeding on a type of algae called diatoms and smaller nematodes. Those red-colored cells in the photo are actually food particles making their way through the digestive tract.

Epsilonema nematodes boast unique-shaped bodies that resemble the number 3 or letter E, and the rings surrounding their bodies secrete sticky mucous.

Bik said the rings surrounding their bodies allow the nematodes to use a caterpillar-like creeping movement as they "walk" over sand grains. 

It's easy to see why the Eubostrichus nematode has acquired the nickname "Chewbacca." Each one of those hair-like structures is actually an individual bacterial cell that's attached itself to the nematode.

These are known as symbiotic bacteria because they have a mutually beneficial relationship with the worm.

What surprised Bik and her colleagues the most is how similar these microscopic nematodes look like macroscopic worms you find in soil and elsewhere on Earth. Like this Gammanema nematode, which tends to live in sandy seafloor habitats.

While they may resemble a harmless earthworm, these long and muscular microorganisms are actually voracious predators, thanks to their V-shaped mouths with numerous rows of teeth-like projections.

What distinguishes the Metoncholaimus nematode is a wide oval-shaped mouth that contains one large tooth and two smaller equal-sized teeth.

Bik said this predatory worm has recently been used in lab experiments to test the toxicity of certain pesticides.

This Pareurystomina has a large mouth that boasts one slender tooth and many rows of tiny serrated teeth-like scales known as "denticles," which it uses to munch on marine microbes like diatoms and dinoflagellates.

This predatory nematode called Pareurystomina is characterized by its thin, pointed tail.

The resourceful Theristus nematode often emerges from between sand grains into the water, and can actively swim towards new areas of sand where more food is available.

The Tricoma secretes a sticky mucus that makes sand stick to its body, which is both a camouflaging defense mechanism against predators, and a weight to prevent strong currents from washing them away.

This species of nematode is distinct for its triangular head and circular "rings" that run along its entire body.

You won't find Thoracostoma nematodes on the beach — but they're not too far off. This species only lives within the roots of giant kelp off the California coast.

There, they feed on small crustaceans. As for those circular clumps of red cells in the photo, scientists believe they function as primitive eye spots to help these nematodes sense light.

Bik and her team are currently on a National Science Foundation-funded expedition to East Antarctica in pursuit of deep-sea marine nematode samples.

"I've recently been working in Antarctica because not many scientists have studied what lives in remote, polar regions," Bik said. "We're comparing Antarctic nematodes to species that live in other parts of the world to see if they're distinct evolutionarily."

Correction: April 26, 2023 — An earlier version of this post incorrectly described the nematodes in this article as parasitic. While some nematode species are parasitic, none of the ones in this article are. 

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