It has a tiny yellow filter (like a flower) on the end which comes out just like flowers open and then retracts into the trunk - the trunk then retracts in upon itself like a telescope. The main trunk (looks a bit like an elephant trunk and a similar colour)
I am assuming it is harmless as appears to be filter feeding?
Peanut worm: The Sipunculids-aka Peanut Worm burrows into rocks and crevices often hiding during the day time and only coming out at night time to feed. They eat microscopic organisms, and detritus they get out of the live sand. The length of a large Peanut worm, when stretched out, is about 6 or 7 cm.