The wifey was re-arranging some Fiji rock we recently used to set up her new 29gal in her office, and this little dude fell out of one of the rocks. I have never seen anything like it before. The "bulbous" body is about 3/4" long, and has a brown and white colored tentacle that extends out about 1 1/2" (also retracts completely inside the "body"). As you can see in the pics, it eventually used the tentacle to bury itself in the gravel bottom, and we haven't seen it since. It's probably something common, but we've never seen one. Whatever it is, it must be pretty tough, as this tank is in the peak of the Nitrite cycle, and this was fully cured rock.