Sea urchin

You can also call them sea chestnut or sea hedgehog. They can be black brown or slightly red. You can eat them raw directly out of the sea. If you ever want to try it's delicious! Attention to thorns, I fell in the sea urchins being child and I still have two thorns stuck in my skin they are very thin and brittle.
You have to open them with a knife and eat the genitals that range from light yellow to dark orange. The dark orange (females) have more taste than the clearest.
It's great to dive to climb the sea urchins themselves and then eat them on the rocks with friends ;-)