Sea pumpkin on the beach

Before a sea pumpkin becomes a ... well, sea pumpkin, it spends it's life as a spiky sea urchin living in a rock pool or gully somewhere on the coast.  But once the creature inside the shell dies the spikes fall off and only a green "pumpkin" looking shell is left behind.  These sea pumpkins are very popular with people, specially kids, picking up shells.