Do sea urchins shed their spines?

[sea horse]

I have a pin coushion sea urchin and it has some"bald" spots on it and there is a little pile of spines at the bottom of the tank. :notsure: I don't thimk any of my crabs would have done it beacause the sea urchin is on the top of thetank glass. What could have caused him to lose his spines?

 

[meanteen]

some time the sea uchins spikes get stuck and the fall off but they should grow back.

 

[reefreak29]

they will shed there spines if there stressed