We had one in the overflow on our invert tank, does that count?
Not sure how it got in there from the main tank, but we just left him be for about 6 months. Bright green, very interested in us--it would duck to hide, then sneak back out to watch us watch it. Scary--did have to remove it a few times to clean the sponges. We'd pull the sponge out, and usually dump it into a basin of water. Had to grab it once--used tongs--and man could that thing smack the heck out of those tongs! Would have broken skin, and our little monster was only about 1-2 inches long.