Sea urchins really do use their little spines like fingers, to move shells onto them — rather like milliners, except the hats go on top of their bottoms so they don’t dry out and they can expel waste.

I will never look into a rock pool again and not notice the urchins with their very cool mussel-hats or the orange starfish which can grow again from just one leg, but only in protected virgin water like this...