But the body of the Geoduck is so big that it spills out from the shells in a long neck called a siphon. Geoducks live in holes in the mud. They dig down into the mud and stretch their long siphon back to the muddy ocean floor so they can breathe. And those are the bubbles you see. They are the carbon dioxide produced by the Geoduck's breathing.
Geoducks can be enormous.
Big Geoducks can weigh as much as 12 pounds.