What is on my urchin??

[arg101]

What that heck is on my urchin?? He has been carrying it around for almost a week and it has not moved. Its fluorescent and only appears yellow under blue light.

 

[56longroof]

Almost looks like a small chalice coral.

 

[Danjoethepirate]

Looks like a snails operculum.

 

[logibear]

Not saying it isn’t a snail but I’ve never seen a snail shell glow like that. My guess would be part of a coral frag