A genus of oval or cigar-shaped, single-celled organisms (family Parameciidae), 50–330µm in size, that swim by means of cilia and feed on smaller cells, including bacteria and fungi, by using their cilia to sweep items through an oral groove and into the gullet. Paramecia are very common in fresh, brackish, and salt water and have long been used as model organisms. There are many species, occurring worldwide.