I had something show up in my tank today and I don't know what it is or where it came from. It looks like a yellow spider. It is about the size of a dime with long spindly jointed legs. I can't get a real good look at it because of where it is in the tank. It seems to be eating the molted exoskeleton of my shrimp. I can't find anything that looks like it anywhere. Any ideas?