Eeek - been there, done something similar.
Went swimming off a beach near Dakar. Nearing my limits, did the obvious thing - stopped, and put my feet down. In a bed of sea urchins.
While you are all having a quiet snigger, just think what your body's first reaction is going to be. Lift your feet? Land in the sea urchins, bum first? Yup.
My a**e, legs, and feet looked similar. Two weeks lying on my front. Despite my other half gently extracting the hundreds of spines, ever so carefully (did she HECK!), they turned nastily septic.
There was a good ending. Sea urchins taste delicious - and I will eat them now at any and every opportunity!