ID on a worm

[flipzed]

so was sitting there watching the tank tonight and i saw somthing creeping outta the cave it had like white antennas 3 i beleive maybe 4, anyways it latched on to a hermit crab and tried pulling it in to its hole. it had a white body with white antennas and i saw atleast an inch of his body thru another hole in the rock. i know for sure its not a bristle worm ive seen those before. has anyone seen one before or know what it is or called?

Thanks