BAR HARBOR – The newest addition to the Mount Desert Oceanarium’s lobster colony looks half-baked.

But it’s nothing personal.

The rare 1-pound crustacean, caught earlier this week in Steuben, is a genetic mutation with a two-toned shell.

One side is the usual mottled dark green. The other side is the orange-red shade of a lobster that’s already spent some time in the hot pot.

The odds of this kind of mutation occurring are very rare – something like one in 50 million to 100 million, according to oceanarium staff. The chance of finding a blue lobster is far more common, at one in a million.

“Isn’t he pretty?” Bette Spurling of Southwest Harbor cooed Thursday as she stroked the lobster’s shell to calm him down. “It’s quite a drawing card for people because they’re quite unusual.”

Spurling is the wife of a lobsterman and works part time at the oceanarium. She explained that lobster shells are usually a blend of the three primary colors – red, yellow and blue. Those colors mix to form the greenish-brown of most lobsters. This lobster, though, has no blue in half of its shell.

That was a shock to longtime lobsterman Alan Robinson, who hauled him out of Dyer’s Bay in Steuben.

“I didn’t know what to think,” Robinson said. “I thought somebody was playing a joke on me. Once I saw what it was … it was worth seeing. I’ve caught a blue one before. But they claim this is rarer than the blue ones.”

In his 20-plus years of fishing, he has never seen a lobster like this one.

“It was something with the line drawn so straight like that,” Robinson said.

Bernard Arseneau, the former manager at the oceanarium’s affiliated lobster hatchery, drove to Lubec on Wednesday to pick up the two-toned creature. He explained that lobsters have a growth pattern in which the two sides develop independently of each other.

“Even regular colored ones have a left-right sort of growth,” Arseneau said.

Children visiting the oceanarium were struck right away by the unusual coloration.

“Dude, it’s half orange and half, like, regular color for a lobster,” exclaimed Alyssa Bonin, 12, of Webster, Mass.

Robinson donated the colorful crustacean to the oceanarium, which often is the beneficiary of strange things that fishermen pull up from the sea. It has received only three two-toned lobsters in its 35 years of existence, officials said.

“Fishermen have been super to us over the years, bringing things in to us,” said David Mills, the co-director and owner of the oceanarium. “Our charge is to teach people about the marine life and commercial fishing in Maine.”

Mills intends to keep the two-toned lobster over the winter and have him on display for educational purposes, though he has no plans to name him.

“Lobsters are interesting but not personable,” he said.