👉 Urostylids are a group of small, round-shaped animals that belong to the class Nematoda, which includes nematodes and protozoans. They have a single cell with two nuclei, an outer membrane, and a central body (nucleolus) containing a large number of organelles. Urostylids are typically found in freshwater environments and can be found in aquatic ecosystems such as rivers, lakes, and oceans.