Urchin Emergency

[Leone]

I bought this urchin but it ate a snail and was attaching itself to the starfish what can I do?

 

[Tahoe61]

An Urchin is not capable of eating a live snail.
That looks to be a type of Variegated Urchin. The Urchin will attempt to place items such as snail shells, frags, algae on the top of it's self for UV protection.
The feeding strategies of Linkia Starfish can be problematic in anything less than a very large and established system.