What swims around Pleasure Bay gobbling up sea jellies?

A mola mola, which was first spotted in the watery corral Tuesday.

New England Aquarium spokesman Tony LaCasse said he believes the mola mola went into the bay, which is just off Castle Island, to eat the large population of jellies that have been making their home there.

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“When I was there, you could observe it doing a lot of feeding,” said LaCasse. The mola mola, also known as a giant ocean sunfish, is uninjured, which means the aquarium will not remove it from the bay. LaCasse thinks it is likely the mola mola will simply leave when the amount of sea jellies dwindles.

LaCasse visited the area last night to check out the bizarre creature, which he said was swimming in a zigzag motion as it grazed.

Some experts believe the hungry mola mola is a juvenile and probably weighs a few hundred pounds or more, said LaCasse. He described the creature as a “giant, thick disk.”

According to Smithsonian magazine, the fish can grow to be more than 10 feet long and can weigh 5,000 pounds.

LaCasse said anyone who sees this mola mola, or any other, should be unobtrusive, but also, should “thank their lucky stars and grab their phone cameras.”