A fun fact that I learned on Twitter is that sea urchins will put on a tiny hat if you give one to them. And marine biologists have been doing just that. 3D printing a bunch of differently styled hats and taking pictures much to our enjoyment.
In nature sea urchins will use shells as hats. They use their use their tube feet and spines to move the hat onto the part of their body where UV rays might touch. The theory is that they do this to protect their bodies from the harmful rays, just like humans do with baseball caps on a bright sunny day.
Riosouza on Reef2reef has been 3D printing these hats which come in all kinds of shapes and sizes. Check out some of them below.