Spathidium 

This graceful ciliate is called Spathidium, subclass Haptoria (Protozoa, Ciliophora).
They are predators. They use toxicysts (an organelle in which the filament carries a poison that can kill other protozoa) for capturing other ciliates for food.
Spathidiid ciliates prefer semisterrestrial habitats, but many occur also in freshwater, and some are marine. I found this one in a dish under a plant in my garden.
Video and photos obtained using a Tomlov DM202 Max digital microscope, observing several drops of water in a concave microscope slide.
Original music and video "Stowaway" by My-Fi Saloon @my-fisaloon8370