The geoduck clam is the biggest clam in the world. Pictured here is a teensy two year old, but they can live to be 150 years old, or older. They frequently weigh more than 5 pounds. And yes, they're ridiculous.
Geoduck live deep in the sand, and while they can retract their neck to avoid predators, they can't retreat completely into their shells, like horseclams can.
One geoduck with broken shell, two horseclams.
Eye of horseclam
Disco Duck