What is this?

[shooter2377]

So I posted the other day about something drilling in to my live rock and didn’t get much of a response. I got a better picture of what I think did it, but not sure. I see it sticking out at different heights, but it doesn’t react when you touch it. It’s hard like a shell, but isn’t solid as it moves around a bit. Any ideas? Oh yeah, I cleaned up the dust in the same area too…

 

[Thomas Jedlicka]

i cant say but I dont know of molluscs like clams or mussels that drill like that apart from a boring clam but it does not resemble it imo.