Dead sea urchin

[Nwel99]

Just picked up this sea urchin 2 weeks ago for a huge algae spike.. water permiters were all good
I just noticed it now though
Where did it go and the Spikes?? So sad
My stock is harmless. 2 clowns and starfish
Also came across this . Thought it was neat . Not sure where it came from
Could it have been inside with the urchin?

 

[blaxsun]

Trying to use my imagination... Nope. All I'm picturing is a hollowed out sea urchin, sorry.