NORWALK — It’s not easy to stump the marine experts at the Maritime Aquarium.

But that’s exactly what happened after fishermen from Copps Island Oysters hauled in four unusual, clawed critters last week on the south side of the Norwalk Islands.

Dick Harris, marine specialist for Copps Island, said the fishermen were unsure of what the creatures were — and what to do with them — so they tossed three back and one brought to the aquarium.

Aquarists identified the 2.5-pound crustacean as a male dungeness crab, native to the icy waters of the Pacific.

“We’re doing our own research on this right now,” said Sandi Schaefer-Padgett, senior aquarist at the aquarium. “It’s not normal. We don’t often get things that no one’s seen before.”

She said no one believed it could possibly be a dungeness crab until they finally identified it. Once they did, the Googling began, and a tank was set up for the yet-to-be-named out-of-towner.

Dungeness crab, named after a small town in Washington state, has been harvested commercially along the Pacific coast since the late 1800s. It is known for its sweet meat, and is one of the most valuable commodities on the West Coast, worth nearly $170 million in Washington, Oregon and California in 2014, according to Washington Department of Agriculture.

The crab has been reported in recent years in the Atlantic, off the coasts of Florida, North and South Carolina and Alabama. The most recent report of the crab in the Northeast was in 2006 off Massachusetts.

Though considered an invasive species, experts from the state Department of Energy and Environmental Protection said there’s no reason to panic. Yet.

“We’d have to wait and see if more are caught,” said Mark Alexander, DEEP fisheries division director. “But I don’t think there’s an immediate cause for concern. It is interesting that they caught more than one, and if more are caught we will want to know the gender.”

Schaefer-Padgett offered a couple theories about how the crabs came to be in Long Island Sound. It’s most likely someone purchased them at a market and set them free. The mystery, she said, is that four were caught in the same area, which means it’s possible they somehow migrated here.

She said there is less of a threat if they were released, because it’s unlikely any females would have been among them. According to the Oregon Department of Agriculture, only mature male crabs 6.25 inches across the shell are harvested. Juvenile males and all females are returned to the Pacific waters.

The crab at the aquarium is living in isolation while researchers work to identify algae and barnacles attached to his shell. Schaefer-Padgett said if the additional organisms came with him from the Pacific, they could also pose a threat to local ecosystems.

“They can bring diseases and plant life we’re not familiar with here that can be harmful to everything else that lives in the Sound,” she said.

Schaefer-Padgett said fishermen should contact the aquarium and DEEP if more crabs are found.

The aquarium guest appears to have adjusted to his living quarters, and has taken to side-sauntering across his home with ease. His buggy eyes pop up when curious onlookers approach his tank, situated behind the scenes of the shark exhibit.

“He’s going to hang out with us for a while,” Schaefer-Padgett said. “We’re all taking a crash course in learning about crabs right now. It will probably be up to DEEP where he goes, we could make an exhibit or I guess we could eat him.”