Is the slug a flattened oval (Phyllaplysia) or does it have a round body with a long tail (Oxynoe)? From the pictures it looks like an Oxynoe, particularly Oxynoe viridis which eats Caulerpa. See this page for some images http://www.seaslugforum.net/factsheet.cfm?base=oxynviri
I was just about to make the same post.. I was going to call it HORNY WORM.. I have 2 of them in my fuge. I am glad to hear they are safe. They have these little anteni looking things on their head too. Freaking weird, I was going to catch them and trash them..
leslie. on that addy you posted there is a picture of the egg pattern they make when they lay eggs. apparently, i have a circular group of newly laid slugmeister eggs! old slugmeister knocked up the misses!