First off, I'm pretty sure that is a pocillopora, not a birds nest.
Secondly the shell is a Certh Snail shell. It could be a crab living in the snail shell since I can't se any of the body, but I'm not sure.
did you try to take the snail off with your fingers? The coral looks good to me and sure doesn't seem like it is affecting it
It may be dead and the coral started to encrust around it. Also that is 100% a neon green birdsnest not a pocillopora.
seriatopora guttatus.
My snails are always fast to come check out any new frags that are added. They're always there. Maybe it's a change in ages for them... Like eating out!![]()
Seriatopora guttatus.
I miss having these snails.
Honestly just to watch them scurry about for scraps.