What happened to my starfish’s leg?

[Neptune 555]

I have had a red starfish for 11 months… yesterday one of his legs is missing? It didn’t melt off as in was looking bad it is just gone? Oddly yesterday I added a pink sea urchin and 2 cleaner shrimps? But I have had those live happily w my starfish previously?

 

[Uncle99]

Vote urchin.
Can eat rocks.
Probably just got in the way.

 

[VintageReefer]

Are the white spots on the other leg/s glare or damage?