Dr Ron,
Hello there. I saw this guy (or its brother/sister) six months ago in my tank and my pictures were too fuzzy for you. I managed to capture it last night, is this a polyclad flatworm?
I didn't find much information on them online, I found this:
http://www.reefkeeping.com/issues/2003-08/rs/index.php
http://www.rzuser.uni-heidelberg.de/~bu6/flatintr.htm
It seems their diet can range from algae to clams. Any way of telling what this one eats?
Also, I had to do a flatworm exit treatment on my main tank a couple of weeks ago, it killed off all the small red flatworms, why didn't it take this guy out?
Thanks!
Brian