Gigas giant clam

The Gigas Giant Clam is a sea creature in introduced in the 1.3.0 Free Summer Update.

In
When donating to the museum, Blathers will say the following:

"Gigas giant clams live in warm-water coral reefs and are the biggest bivalves in the world. Growing as wide as six feet and weighing up to 600 pounds, these clams can live to be 100 years old. And yes, these mighty creatures look as though they could eat a swimmer whole. But they eat plankton instead and get valuable nutrients from an algae they live in symbiosis with. Indeed, these enormous gents get all the sustenance they need by lying face up with their shells half-open. If such was my life, I'd be happy as a clam too."

Real-world information
Tridacna gigas is one of the most endangered clam species. There is documentation of their existence as early as 1521. One of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans, they can weigh more than 200 kilograms (440 lb), measure as much as 120 cm (47 in) across, and have an average lifespan in the wild of over 100 years. They are also found off the shores of the Philippines and in the South China Sea in the coral reefs of Sabah (Malaysian Borneo).