If a millennial sees an unusual animal, the first reaction is often to pull out a cellphone.

A stingray not ordinarily found in shallow waters was spotted by a young woman Sunday who did just that — capturing the creature on her phone’s camera, officials said.

Louisa McCullough, 18, of Hingham, was on a small boat about 50 yards off the shore of Martha’s Vineyard when she saw a large creature moving across the bottom of the water, the New England Aquarium said in a statement.

McCullough said she could see a triangular animal about eight feet deep in the water that looked to be about 6 feet wide with a long tail, officials said.

“Being an 18-year-old, her cellphone was at the ready, and she shot video of a large animal,’’ the aquarium said.

McCullough sent the video to The Vineyard Gazette, where she works as an intern. The newspaper then turned the images over to the aquarium, where the creature was identified as a roughtail stingray.

The roughtail stingray frequently migrates to the waters of Southern New England, officials said, but is rarely seen in water that shallow.

The aquarium said the stingrays tend to prefer sandy and muddy water in areas ranging from 30 to several hundred feet deep.

The animals have thorny plates on the lower part of their body and tail, as well as defensive barbs at the base of their tails, the aquarium said.

The creatures are usually nonaggressive toward humans, unless someone steps on their tail or brings them onto a boat, according to the aquarium.

“Thanks to the ubiquity of cellphones, the wonder of encountering a mysterious sea creature can be both solved and shared,’’ the aquarium said.

Olivia Quintana can be reached at olivia.quintana@ globe.com. Follow her on Twitter @oliviasquintana.