Stentor species that live individual are too small to be noticed. The species that form colonies are so extremely common that they can be
recognized under water. They are usually attached to a substrate like plants, algae and other detritus, but they can also appear swimming. Some reach several millimetres in length, making them among the largest single celled organisms.
Around the trumpet-shaped opening is a ring of cilia which initiates a flow of water. In this way, Stentor captures food particles. The rest of the body is also equipped with cilia. Fully extended, Stentor is trumpet-shaped, but they can contract strongly; then they are almost round. The narrow end can elaborate a sticky substance that aids the protozoan in adhering to a substrate.