How do you know when your urchin is dead?

[Redbird5]

I have a tuxedo urchin in my aquarium. Last night I noticed that it was in a cave in the sand and my peppermint shrimp was on to of it doing something to it. This morning I couldn't tell if it moved or not. It does move very slowly and can spend days in the same spot. He's always been on the glass grazing on algae, but never in the sand until last night/this morning. Any idea what's going on?

 

[scooterh928]

Losing his needles and eventually loses them all and becomes hallow

 

[fishguy242]

Move it to glass ,see what happens,if dead remove rt away.

 

[Redbird5]

Move it to glass ,see what happens,if dead remove rt away.

From what I can tell he has all his needles. I'm wondering what my peppermint shrimp was doing last night, but he's kinda weird anyways.