For the past two days while guiding a group of students from MGS at Changi beach, I noticed this segmented like thing coiling around the mouth or Aristotle's lantern of the white sea urchin, Salmacis sp.
I thought that it was a parasite initially (it does look like a leech) but r and ks mentioned that it could be part of the urchin's body. Until today, when I saw that the worm started to move about around its host's mouth am I certain that it is not part of its body! Such an interesting discovery. I wonder if this worm just scavenge on the food which this urchin feeds or is it a blood sucker?