Cockle shell

Cockle is the common name for a group of small, edible, saltwater clams, marine bivalve molluscs in the family Cardiidae. Various species of cockles live in sandy sheltered beaches throughout the world.
The distinctive rounded shells of cockles are symmetrical, and are heart-shaped when viewed from the end. In most but not all genera there are numerous radial ribs..
The mantle has three apertures (inhalant, exhalant, and pedal) for siphoning water and for the foot to protrude. Cockles typically burrow using the foot, and feed by filtering plankton from the surrounding water.
Cockles are capable of 'jumping' by bending and straightening the foot.