Several weeks ago, the Plecostomus fish in our tank at work died (it seems to be a difficult time for fish), and the tank has been getting progressively more obscured by algae growing on the glass. Plecostomuses (or perhaps Plecostomi?) feed on algae by scraping it off with their sucker-like mouths, and are ruthlessly efficient at keeping the tank clean. David has a nice picture of his pleco, George, doing just that here.
When I came in this morning, I was surprised to see a huge (well, 15 cm long) new pleco in the tank, busily suckering its way around the glass. It's a mesmerising sight from the other side, watching the mouthparts working away at a frantic pace. I once had to catch our former pleco when we had to drain the tank temporarily. I don't recommend it as an experience; it suckered itself on to my palm and started rasping away, making me go "Yeurghh!". It didn't hurt, exactly, but it was a mildly unpleasant surprise.
Now we have to think of a name for New Pleco.