My brother told me that he saw a small speck in his aquarium today and claimed to me that it was a sort of an arachnid. I, on the other hand, thought it was impossible for him to notice it let alone identifying. Turns out he was right. It was an arachnid indeed and according to my calculations no bigger than 200 microns. Such an observer! This article is dedicated to him.You can see the animal forcing his way through surface tension of the water. Here are the pictures of the speck under 40x magnification and two different lighting conditions.