Just below the surface

No doubt, the beach is a bonanza.

Just probably not the way you’ve always envisioned it.

Underneath that sandy ribbon of ivory patted by the sea is a tumult of life that is invisible to the naked eye.

As sunbathers burrow their bare feet, erect sandcastles, or embark on shovel campaigns to China, millions of microscopic creatures linger below: worms with mouths full of pinchers, antennaed crabs, mites with robust armor. They are clear and white, and little larger than the specks of sand that serve as both their welcome mats and dinner plates. They have hooks and adhesive organs to grasp prey and grip tight when the current slips in.

“When you look at a sandy beach, you don’t expect much in it,’’ explained Seth Tyler, a professor at the University of Maine who studies these miniscule beach dwellers, known as meiofauna. “They’re there by the billions and billions. They’re very common, very plentiful. It’s an amazing, unseen world.’’

Well, not completely unseen. The emerging study of meiofauna is excavating a rain forest-rich ecosystem of infinitesimal creatures, sized up in millimeters and micrometers and representing a diversity of worms, jellyfish, amoebas, mites, pedes, shells, and crustaceans. In just a handful of sand, tucked among the grains, there are probably thousands. In a bucketful, millions.

Before you toss out your bathing suit and resign yourself to a life of pale skin: They’re not disease-harbingers and they can’t hurt humans. Nor do they have any use for or interest in us, Tyler stressed.

Even so, they might chime the icky-alarm.

On a recent visit to Salisbury Beach, Kristyn Nickola of Lawrence said she was “shocked’’ by the revelation that a Lilliputian world was teeming just below her sunbathing spot.

“It kind of makes me not want to come now,’’ she said as she dried under hazy skies.

Her cousin, Crystal Nickola of Lowell, having also just taken a dip in the chilly Atlantic, agreed that “It kind of creeps me out.’’

Still, the slightly unsettling knowledge will not derail her weekly summer beach visits. Overall, it’s “surprising,’’ she said, clumps of damp sand - the very sort that serves as the suburbia of meiofauna - lingering on her bare feet.

Other beachgoers had a similar reaction: A sort of unsettled fascination.

Pepperell resident Beth Dunn, curly hair corralled by a baseball cap, kite jerking above, and feet incubating in mounds of sand at Salisbury, said the creatures sounded “kinda gross’’ but also “neat.’’

“Does that freak you out?’’ she asked 7-year-old Emma, plopped in the sand in a pink striped dress beside her, wriggling toes half-buried.

“No, I don’t mind,’’ she replied. “It’s cool, kind of.’’

“Can’t see ’em, can’t worry about ’em,’’ Dunn added.

That’s the attitude Tyler likes to hear; these animals, he said, should allure rather than frighten.

In fact, some of them, including the gnathostomulida, a long squiggly worm with pincher-jaws, feed on rogue fungi and bacteria that can be harmful to humans. “They’re not at all dangerous, not disease-causing,’’ Tyler explained. “There are more dangerous things in your backyard soil.’’

And because they’re so small, “It’s not as if you could even feel the tickle of them crawling on you,’’ he noted. “You’d never notice.’’

But they’re not so benign in their own miniature kingdom.

In particular, the soft-bodied worms Tyler studies are pitiless predators, stalking victims such as planktonic organisms that get turned around in the tide and trapped within sand grains.

Their artillery? Head-top hooks, claws, and adhesive organs. “They’re among the most voracious predators in the sand,’’ Tyler said. They’re the “terror of the meiofauna.’’

Still, whether predator or prey, these diminutive creatures residing below the Frisbee games and the beach blanket bingo have evolved to survive in an extreme ecosystem.

Mostly inhabiting damp sand, they keep from washing away by gripping the grains with suction cups, sticky feet, claws, and tubes secreting cement-like substances.

Their versatility allows them to be vast: They’ve been found in the briniest deep of the ocean, as well as in freshwater rivers, inlets, streams, lakes, caves, and even hunkered in sea ice, where they hole up in tiny pores and channels.

All told, there are somewhere between 10 and 100 million miniature species that consider the sand their metropolis, only less than 10 percent of which have yet been identified, Tyler said.

But just with the roughly 1.5-to-2 million animals cataloged, the diversity is incredible, he said; the shapes are so wide-ranging and unique they’re beyond the imaginations of science fiction writers.

For instance: worms in the shape of teardrops, spiky cucumbers, and blunted bowties, some with full bodies of hair, some so transparent they seem little more than Vaseline diagrams; copepods, or crustaceans with ribbed behinds and long tentacles that look like a fusion of shrimp and catfish; and other critters with any combination of protruding antennae, mawing mouths, pinching claws, bulging bodies, beards, and spindly legs.

For Tyler, the fascination is in the evolutionary aspect. Some of the worms he has studied up and down the East Coast and abroad originated more than 650 million years ago. “These are some of the most primitive animals,’’ he said.

Despite their longevity, it wasn’t until the 1920s that German Adolf Remane started digging in the sand for evidence of minuscule life, Tyler explained. Today, several hundred scientists from the United States, Europe, Brazil, Australia, Russia, India, and many other countries peer among sand grains to study the various beings within.

Going forward, as knowledge broadens and more species emerge, these creatures may play a role in the study of global warming.

Calling them an “indicator species,’’ Tyler said all manner of meiofauna are sensitive to pollutants and climate change. Overall, they are “quite important to understanding the health of the oceans,’’ he said.

In the end, even Kristyn Nickola came around.

As she lounged in the dim sunlight on the beach, she scooped up a handful of damp sand and gently sifted through it.

She shrugged. “I wouldn’t want to step on them.’’