What is this huge worm that's as hiding in a rock

[BurtMacklin]

I pulled a piece of rock out to kill vermetid snails with a dental pic. I thought, "let's flip it over and see if there's anything underneath by chance". I see the thin end of this worm-looking thing sticking out. When I touched it with the pick it retracted into its hole. I pulled the sand and some rock away to get into its cave that looked carved out. I pulled on the thin end and got most out before it broke. I went back and pulled out this huge thick end. What in the world in this thing? Just soft brown material inside of it.

 

[ying yang]

Look up peanut worm .
Possible could be one off them by your description