Does it sort of unroll like a sock? If so, it is probably some sort of Sipunculan and it is harmless.
AquaC Remora Pro
140#s Live Rock from LiveRocks.com
Frogspawn, Hammer, Zoos, Leather Frag, and Xenia and Green Star Polyp frags from fishfreek and Alarmguy66, Thanks!
Member of the Unofficial A-Team