OMG a monster in my tank!

[corpusse]

I think they only eat Mullusks not corals. At least the kind I had were. Mine were darker and had spots so I think what you have is a different species.

I would check your tank for more at least if some rocks can easily be moved. Another place to check would be on the bottom of clams. I'm not suggesting you tear down your tank but if you have any areas that are easy to check it's worth a look imo.