In this pond sample dip Closterium parvulum are pretty prolific with hundred of them in each water drop, so the incidence of finding clusters of reproducing specimens are fairly common. Unfortunately, this is also one of the smaller species of Closterium, so even at 40x and stacking, this is the best I can get with my setup. Still, the stages of development are interesting.
Images made through a microscope. All subject types.