What's doing this?

[Bug530]

Looks like something is eating away at the skeleton of my torch.

 

[EagleEye121]

It almost looks like the coralline is being eaten rather than the skeleton. Do you have urchins in the tank?

 

[tbrown]

+1 to possible urchin. I had a Pencil Urchin that would eat the skeleton of corals, especially if the skeleton had coralline growth on it.

 

[Bug530]

I have a purple pincushion but this makes me feel better about getting rid of it when I upgrade to a bigger acrylic tank.

 

[Privateye]

I've seen long spine urchins do that. Reliably. So +2 on the urchin question!