The ocean sunfish or mola is found in most of the world’s oceans and is not unusual in Boston waters. Nevertheless, seeing one was obviously a shock to Michael Bergin and his friend Jason “Jay” Foster who came across one while fishing in Boston harbor. Bergin starts yelling, using colorful (Not Safe for Work) language, to express his amazement at what he identifies variously as a sea turtle, a baby whale, a flounder, a tuna and “Moby Dick.” The video is oddly amusing and has gone viral with roughly a million views so far. The Boston Globe suggests that Bergin is “basking like a sunfish in Internet fame.”

National Geographic describes the fish that so freaked out Michael Bergin: As gigantic as the ocean sunfish can be, it still seems like only half a fish.

Sunfish, or mola, develop their truncated, bullet-like shape because the back fin which they are born with simply never grows. Instead, it folds into itself as the enormous creature matures, creating a rounded rudder called a clavus. Mola in Latin means “millstone” and describes the ocean sunfish’s somewhat circular shape. They are a silvery color and have a rough skin texture.

The mola are the heaviest of all the bony fish, with large specimens reaching 14 feet (4.2 meters) vertically and 10 feet (3.1 meters) horizontally and weighing nearly 5,000 pounds (2,268 kilograms). Sharks and rays can be heavier, but they’re cartilaginous fish.

Mola are found in temperate and tropical oceans around the world. They are frequently seen basking in the sun near the surface and are often mistaken for sharks when their huge dorsal fins emerge above the water. Their teeth are fused into a beak-like structure, and they are unable to fully close their relatively small mouths.