Ok so I googled Horsehair and there is one marine genus. It mates and layes eggs, 80 some days later the eggs hatch and are eaten my crabs, infected crab dies due to worm and worm exits host. Then the cycle starts all over again. But this doesnt explain why the string was coming out of the zoas. I was watching one of the strings and it broke off. I tried to turn off the power heads but I lost the string when I looked away. Anyone have any Clue?