Looks like a peanut worm to me. Is it nocturnal? Peanut worms come out at night and most will pull back in quickly when hit with a flashlight.
There seems to be some variation in color - most of them are grey/brown and some are striped to varying extents.
The "trunk" is the only part you'll ever see - they have thinker bodies that stay inside the rock. When they extend their trunk it kind of looks like it's unrolling from the inside - if that makes any sense. Reminds me of pulling a stocking inside out. The end has a little spiky mouth part that scrapes the rock when it's completely extended. The pictures on Chuck's addiction show the mouth part pretty clearly.
http://www.chucksaddiction.com/hitchworms.html