subterranean marine worm

I have seen these same egg sacs. The only images I found online that resembled these were for polychaete worms. I dug one of these out of the sand, and it was attached to a very thin tube made of sand. The little tube was surprisingly strong.

I don't think it's a salp. Lives in shallow water with its body inside a burrow. I've been told its a worm and the sack is its egg(s)