I was also today years old when I learned sea urchins wear hats. Living Morganism brought this to our attention with this tweet. The photos are from VanillaBean5813! Their sea urchins like to cover their heads so they 3d printed them some hats! Before they made them these hats they had been picking up shells or small coral, which was damaging to the coral babies. They made a top hat, cowboy hat, wide brimmed hats, witch hat and even a Viking hat:

Source: VanillaBean5813