Q. Last summer, we saw a black turtle on a mud bank in the marsh. It was about the size of a saucer and had a gray neck with black spots. It didn't look like any turtles we'd ever seen. Could it have been a young sea turtle?

A. No, it wasn't a sea turtle. What you spotted was a diamondback terrapin (Malaclemys terrapin). Unlike most turtles that choose either fresh or salt water for habitats, diamondback terrapins live in brackish water in our sounds and estuaries. Oddly enough, they require fresh water for drinking. Terrapins are excellent swimmers and extremely wary. They immediately head for water if approached.

Usually dull colored, these secretive turtles have dark upper shells and lighter, greenish undersides. Their skin, neck and legs can be completely dark, or grayish with black spots or flecks. Their upper shell is marked with prominent circular rings.

Terrapins occur along the East Coast of the United States from as far north as Cape Cod to the southernmost Florida Keys. They're also abundant along the Gulf Coast from Florida to Texas. Mature males are usually smaller than females, measuring some 5 1/2-inches long compared to the female's 9-inch length.

Females reach sexual maturity at about age 7 and lay eggs on shore above high tide. They typically nest several times per season, digging a nest cavity to deposit their eggs. Hatchlings may spend their first years upstream in creeks in brackish or relatively fresh water. As they age, they move to salty marshes where food and nesting sites are plentiful. Terrapins feed on snails and other mollusks, crustaceans, fish, insects and carrion.

These secretive animals were nearly brought to extinction a century ago, when they sold for up to a dollar an inch. Their sweet meat was considered a delicacy and made into soup. Although their numbers have recovered in some areas, they are protected nationally, and in North Carolina are listed as a Species of Special Concern.

Current threats to terrapins include coastal development and entrapment in recreational crab pots. Terrapins, like all turtles, are air breathers.

When crab pots are left unattended or abandoned, they kill hundreds of terrapins. A simple turtle excluder device can be installed, which allows the terrapins to escape.

The state operates three public aquariums; one in Pine Knoll Shores, another at Fort Fisher and a third on Roanoke Island.

The aquariums are administered by the North Carolina Department of Environment and Natural Resources, and are designed to inspire appreciation and conservation of North Carolina's aquatic environment.

For more information about the Aquariums, visit www.ncaquariums.com, or call 800-832-FISH.

Sherry White works for the public affairs office of the N.C. Aquariums.