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photo composite of three microscopic images of worms and an image of someone sitting with their hand in the sand
Thousands of species of nematodes live in your average handful of sand.

Jim Baldwin and Manuel Mundo-Ocampo; Mirayana Marcelino Barros; Getty; Insider

  • 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 parasitic roundworms called nematodes.
Image of the Playa del Duque beach on the Costa Adeje, Santa Cruz de Tenerife in the Canary Islands.

NurPhoto / Contributor / Getty Images

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.
Nematode research Holly Bik pouring water through a sand sifter to tease out some nematodes.
Hillary Bik pouring water over a sample to extract nematode specimens for research.

Virginia Schutte

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.
Microscopic image of the Ceramonema nematode.
The wave, plate-like pattern of this Ceramonema is what distinguishes it from other nematodes.

Jim Baldwin and Manuel Mundo-Ocampo

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.
Microscopic image of Xyala nematodes.
The Xyala is distinguished by its rows of raised ridges all over its body.

Jim Baldwin and Manuel Mundo-Ocampo

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.
Microscopic image of a odontophora nematode.
The Odontophora nematode has an opening on one end that resembles something out of the "Alien" film franchise.

Jim Baldwin and Manuel Mundo-Ocampo

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.
Microscopic image of the desmodorid nematode.
Desmodorid nematodes are covered in tiny sensory hair-like organs that help them navigate their environment.

Mirayana Marcelino Barros

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.
Microscopic image of the enoploides nematode.
Enoploides nematodes have three extendable jaws they use to consume prey.

Mirayana Marcelino Barros

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.
Microscopic image of the epsilonema nematode.
Epsilonema nematodes secrete mucous to help anchor them to the sand and avoid washing away with the tide.

Mirayana Marcelino Barros

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.
Microscopic image of the Eubostrichus nematode
Eubostrichus nematodes plays host to bacterial cells that cover its body in a symbiotic relationship.

Mirayana Marcelino Barros

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.
Microscopic image of a Gammanema nematode.
Gammanema nematodes have few defining characteristics but in the roundworm world, they're vicious predators.

Mirayana Marcelino Barros

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.
Microscopic image of a metoncholaimus nematode.
Similar to the enoploides nematodes, these Metoncholaimus nematode have teeth that help them consume prey.

Mirayana Marcelino Barros

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.
Microscopic image of the Pareurystomina nematode.
Pareurystomina nematodes have serrated scales that help them consume prey.

Mirayana Marcelino Barros

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.
Microscopic image of the theristus nematode.
Theristus nematodes can actively swim to hunt for prey.

Jim Baldwin and Manuel Mundo-Ocampo

Some species can also feed as parasites by attaching themselves to the outside of larger polychaete, AKA bristle worms.

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.
Microscopic image of the tricoma nematode.
Tricoma nematodes are distinguished by their triangular head and body that look like circular rings.

Mirayana Marcelino Barros

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.
Microscopic image of a thoracostoma nematode.
Thoracostoma nematodes has two red circle that look like eyes and, in fact, help the microbe sense light, scientists think.

Mirayana Marcelino Barros

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.
A large red ship that Holly Bik and her team are using to conduct more research on nematodes.
The ship that Bik and her team are on right now to find more nematodes thriving in the deep-seas of East Antarctica.

Virginia Schutte

"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."

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Science, nematode, Microscope Images, Ocean, sand, Features, science-freelance, Insider Illustration, Marianne Ayala
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