Strange pulsing organ in rock

[oool8899]

I turned over one of my rocks recently and this weird pulsing organ thing was in there, it seems to open and close the valves normally then spasms out, any idea what it is, im thinking some kind of worm/wormlike mollusk

 

[Shon]

Middle left, I think I see two tubes and a mass inflate then suddenly collapse.

Maybe a sea squirt in a rock hole?

 

[Reefkeepers Archive]

Judging by the end of the tube I'd say sea squirt (aka tunicate). Harmless/beneficial filter-feeders

 

[Shon]

This guy right?

 

[Reefkeepers Archive]

This guy right?

Yes

 

[Reefkeepers Archive]

Yes

Most common colors in aquaria are clear and brown