ID - Small Blueish Shell/Body

[Spartan_Neptune]

Trying to ID this little blue shell/body thing on the edge of the frag plug, has a blueish colour to it, seems to be just moving around staying on this frag for the past few weeks

 

[jimk60]

Don't know what it is but since the frag looks easily removed. I would take it out and put the critter into a glass of tank water. You can probably get a better picture that way.