People are prone to stereotyping, but we love it when someone flips the script.

So when Hilary Brown asked us what the difference is between turtles and tortoises, we were happy to learn that our notions about turtles were all wet.

Turtle or tortoise?

Sheila Madrak, a San Diego-based wildlife biologist who specializes in sea turtles, has a simple answer.

“All of them are turtles,” she says.

The end.

Okay, there’s more to the story but that part is true. “Turtle” is the umbrella term for all 200 species of the testudine group, which includes turtles, tortoises, and terrapins. All turtles have two distinct features: A shell to which their ribs and vertebrae are fused, and a pelvic girdle that sits inside their rib cage. This “compressed anatomical structure,” says Madrak, is what gives turtles their signature lumbering walk.

Turtles can be aquatic, semi-aquatic, or mostly terrestrial. Tortoises are turtles that live on land and aren't equipped for water.

View Images A green sea turtle, Chelonia mydas, an endangered species, swims over a southern Caribbean reef. Photograph by George Grall, Nat Geo Image Collection

One easy way to tell a tortoise from a turtle is to look at its feet, which are “designed for trucking around on land,” says Madrak.

Or even underneath it, since some tortoises are burrowers, like the gopher tortoises of the southeastern United States.

“They look like tiny elephant feet,” whereas semi-aquatic and aquatic turtle feet are webbed. Only sea turtles have true flippers.

View Images A Sonoyta mud turtle, Kinosternon sonoriense longifemorale, at the Phoenix Zoo. Photograph by Joel Sartore, National Geographic Photo Ark

All turtles also have a gular scute, an extension of the lower shell that sticks out under the chin. Gular scutes are more pronounced in males, who use them as weapons to flip an opponent over in a fight, Madrak says.

Side-necks and terrapins

For some extra complication, there are two suborders of turtle whose classifications are based entirely on how they move their necks.

Cryptodira, which includes the desert mud turtle, can pull their heads straight back inside their shells, but Pleurodira, or side-necked turtles, like South America’s Mata Mata, cannot. They turn their heads to the side and hide them under the rim of their shells for protection.

And finally, there’s the terrapin, which is a turtle but not a tortoise.

View Images A juvenile ornate diamondback terrapin, Malaclemys terrapin macrospilota. Photograph by Joel Sartore, Nat Geo Image Collection

In his book, Turtles of the United States and Canada, Jeffrey Lovich, an ecologist at the United States Geological Survey, describes terrapins as “more or less aquatic hard-shelled turtles,” and says the word terrapin “is itself an Algonquian word for turtle.” Terrapins, like the diamondback terrapin, which inhabits coastal marshes from New England to Texas, prefer to make their homes in brackish water.

Don’t Know? Don’t Touch!

Why would you need to know a turtle from a tortoise?

Sometimes misidentification could be fatal for the animal. In 2015 The Florida Fish and Wildlife Commission had three instances of people who had mistakenly released tortoise hatchlings into the ocean—where the land-dwelling creatures would likely drown.

Our experts’ advice on interfering with wildlife? Don’t.

"Keep wild turtles wild,” Lovich says. “It’s always tempting to take turtles from the wild as pets, especially small ones,” which are adorable but may grow bigger than people expect. (Related: World’s Biggest Tortoise Can Live Up to 120 Years)

View Images An eastern box turtle, Terrapene carolina carolina, walks over autumn-hued leaves. Photograph by George Grall, Nat Geo Image Collection

“If people want a pet turtle, it's best to adopt one from a local shelter that specializes in exotic animals,” Lovich says.

If you find a turtle you think is in distress, call your state fish and wildlife commission or another professional who can identify the species and will know how to handle the circumstances.

That is, if anything needs to be done at all.

These reptiles did okay for millions of years without people, Madrak points out. “There will be turtles when there are no longer Homo sapiens.”