Recently set up marine tank - have had water and live rock for about 3 weeks. Got a clean up crew a few days ago - cleaner shrimp, turbo snail, bumble bee snail and nassarius snail. Today when I was looking at the hair algae I noticed a strange slug/snail on top of one of the rocks. He's about the size of a 20p and has a big about/Hoover nose.. I have no idea how he got in the tank and have been trying to research to see if he's benifical to the tank! Any comments will be appreciated.