If you can't catch it you'll have to set some sort of trap. My guess is that it is nocturnal? There are different traps on the market... some of the guys here can probably tell you how do DIY one. You might try the DIY forum and look through the previous posts.
but I'm pretty sure I saw another. It is only about an inch long or so and when it's in the water it is almost transparent. The one I got is in a bag thumbtacked to my wall........still kicking.........does anyone know what it is?
Almost any fish would eat one if it could. The problem is that they are usually nocturnal and can quickly retreat to their hole. If you can isolate the coral you might be able to get it to evacuate the rock by squirting fresh water into its hole. Just so you know I'm just guessing on how to get rid of it. An Iodine dip might get it pretty upset too.
from previous perch (it was almost detached anyway) relocated to a place where I can monitor the base. All seems well so far. Haven't been able to locate any more of the worm things. Fingers are crossed.