👉 Monostichous, also known as simplest chondrichthyes, is a type of bilaterian fish that has only one set of chordate teeth. This means that there are no tooth plates on the sides or backs of the teeth, and each tooth is symmetrical in shape. Monostichous fish were once thought to be extinct due to their lack of tooth symmetry, but recent studies have shown that they still exist and can be found in various parts of the world