Freaky worm shoots spawn-goo from head!!!

Wish I could have gotten a picture of this thing, but I was certainly in a little shock. I've had this organ coral skeleton in my tank for some time now, and it came with all sorts of cool little bivalves, sponges etc... A few nights ago I see this long flat worm, a little green with stripes, kind of like a long thin freshwater leech. It just popped out of the organ coral and released about 10 HUGE spawn plumes out of the sides of it's head. The part that popped out was about 8cm long with what looked like about six little white jets of spawn-goo shooting out of the side of it's head!:bigeek: This is probably the most alien thing I've ever seen, and certainly one of the creepiest. Also it was only part of him that popped out, then after doing the deed, he retreated. I've since inspected the organ coral, but can't find any trace of him. I still don't know if he's still in the organ skeleton or if he's in the sand, but I'd love to find him again for ID.

First off, what kind of worm is this? Should I be concerned? Is it beneficial, or will it attack other tank residents?

Now that I think about it, the pod population in that particular skeleton has dramatically decreased lately too...

*shivers*

Right now we only have 2 small damsels and a conch as the tank is still new.