Rotaria macrura; sometimes it happens that the water under the cover glass evaporates so much that a rotifer is crushed. So in this case the special was that it seemed as if sperm had been released by this "accident". These "sperm" appeared in some preparations in Rotaria. But: sperm at Rotaria ?? Coincidentally, I came across an article by Dr. Martin Kreutz (Konstanz) in the German Microscopy Forum. He had found the solution. BUDDE (1927) found out that the sperm-like structures are parasites from the Apikomplexa group. Leptoclava parasita invades the bladder, which clearly stands out.