I have a reef tank. In it is a tuxedo urchin. Mine has these hats as well - it’s fairly common amongst us hobbyists, and yes it’s always funny.

Urchins are fantastic and voracious algae eaters. They like to shade themselves from the lights and camouflage themselves. They pick up EVERYTHING. If it’s not glued down, the urchin will be wearing it as a hat eventually. Even if it IS superglued down, there’s a good chance they’ll rip it up and wear it as a hat.

My urchin carried a hermit crab around for days. Poor crab was like “hey man put me down!” He didn’t - a few days later the hermit crab moved to a new shell.

My urchin is one of, if not my most favorite tank inhabitant.