We have noticed that there are Tube worms on our Cerith Snails.
Since Cerith snails burrow into the substrate, and the other snails in our tank do not, this may explain why only the Cerith snails have these worms. They are very tiny and hard to photograph, but if you look very closely, there is a plume at the end of the white tube that captures tiny objects in the water.
If they are touched, or have captured something, they retract into their tube. We feed our reef Phyto Feast, which is a phytoplankton that these tube worms eat. Because they are so tiny it is hard to tell the exact type of Tube Worm or Feather Duster they may be, but either way they are an addition to the biological filtration of our tank and pretty cool.