If you’re afraid of the dark, you should avoid the “midnight zone” in the oceans. It’s so far down that no sunlight ever reaches it. The zone’s inhabitants include creatures with bulging eyes and big, sharp teeth, and some with bright, wiggling “lures” to attract prey.

One inhabitant also looks like the stuff of nightmares, but it’s a threat only to small fish and other tiny creatures: Stygiomedusa gigantea—the giant phantom jelly. Its “body”—known as a bell—is about three feet across. It can expand to several times that size, though, perhaps to wrap up its prey.

Four “arms” trail away from the bell. They can be more than 30 feet long, and they wave through the currents like a ripped-up bedsheet in a summer breeze.

The arms are classified as “mouth” arms—they sense prey in the dark ocean, then grab it and pull it up to the stomach. But unlike many jellies, the arms don’t have stingers.

The giant phantom jelly has been spotted in all the world’s oceans except the Arctic. But it’s not easy to see because it usually stays deep—anywhere from a few thousand feet to about four miles. In fact, since the first one was reported, in 1899, scientists have logged only a few more than a hundred confirmed sightings.

Despite the lack of sightings, biologists say the giants may be common—but hidden in the dark waters of the midnight zone.