ID Please

[beefORchicken]

So there's a strange creature that has made holes in some rock and a worm like arm pokes out like a 'whack-a-mole'. I've never seen it before and i think there's only one animal since only one arm pokes out at a time. Any ideas of what it is?

This picture shows the holes in the rock, the highlighted area is about the size of a toonie

[ScubaSteve]

Never seen that type of boring pattern before but what you describe sounds like a sipunculida or eunicid worm, more likely the former. Just guessing though.

[beefORchicken]

Yes it may be a sipunculida (peanut) worm but I'm not 100%. The holes in my rock are small, ad if it was made by a small drill. Others online describe holes made to be pencil sized. I'll have to do more research.

Has anyone else had rock bored by something before?
My concern is that the rocks could become infested and maybe even weakened to the point of falling apart. Let's hope not.

[ScubaSteve]

I've had boring clams and urchins before and they make holes, but nothing catastrophic. I wouldn't worry about it destabilizing rocks or anything.