Slug like foot extending from rock?

[Generator]

I noticed this flat up against the rock a few days ago because it had a little bit of a flourish to it. Today, it's extended from the rock. The bottom of it, the face is about the size of the pad of my thumb so not a small thing. It's tucked up in a hole in the rock. I've not been able to get a better photo because it slams back into the rock.

 

[Kmst80]

Looks like some kind of filterfeeding worm, similar like a feather dusters or x-mas worm. But that's a pure guess. Cool creature.

 

[ISpeakForTheSeas]

From the description, I would assume a bivalve of some variety, but it's really tough to say from the pic - is the bottom of the foot hard/solid or soft/squishy? When it slams back into the rock, does it swing closed, or pull straight in?

 

[Generator]

From the description, I would assume a bivalve of some variety, but it's really tough to say from the pic - is the bottom of the foot hard/solid or soft/squishy? When it slams back into the rock, does it swing closed, or pull straight in?

I'm thinking it's a bivalve also. The angle I'm seeing it from it pulls straight in. It's on the underside of the rock. I've just turned it so it's on top. I've rearranged a few times since I first placed the rock because interesting things have appeared each day. This is a photo after I turned it, waiting for it to come back out but it looks hard.

 

[Generator]

It's definitely a clam of some sort. It stays mostly in the rock.