When the Nature Conservancy, a nonprofit environmental group based in Arlington, recently purchased the Unthanks Cave in Lee County, Va., many scientists breathed a sigh of relief.

The cave, named for a previous owner, is home to many rare species of invertebrates, including a newly discovered species of blind, cave-adapted snails that live in Unthanks' two streams.

Ownership by the Nature Conservancy "ensures that these animal species will be preserved and protected," said John Holsinger, a biologist at Old Dominion University who has studied the cave and its inhabitants for more than 20 years.

The Nature Conservancy purchased a 22-acre parcel in Virginia's southwest tip that contains the only known entrance to the cave. According to Rita Christian of the conservancy's field office in Charlottesville, Unthanks is the first cave the organization has bought in Virginia. Christian said that before buying Unthanks and land that surrounds it, the Nature Conservancy checked to see if it was listed with the Virginia Natural Heritage Program, a state and conservancy effort to catalogue important animal habitats. When they learned it was, the conservancy purchased it from an out-of-state owner who requested that the sale price not be disclosed.

Unthanks is seven miles long and filled with many wide passages. In addition to its great scientific interest, the cave has also been popular with spelunkers who have admired its stalagtites and stalagmites.