I photographed a flatworm on my aquarium glass (Convolutriloba retrogemma accoording to Delbeek and Sprung). I found a lot more than I expected. The dots in the flatworm may be zoozanthellae. The long strand on the glass may be a a type of blue green algae. I don't know what the pair of egg like structures are in the upper left corner. No wonder it's hard to judge what is going on in an aquarium. You can't see much of the action.