Greetings to all lovers of the world of wildlife! Today I want to tell you about one of the most unusual classes of annelids - primary cavitary worms, or roundworms. These are very small flatworms, only about a millimeter in size. They have only one feature that distinguishes them from other worms: they do not have a diencephalon or other organs of the central nervous system, but they have special nerve ganglia that are interconnected by fibers. One of the characteristic features of these worms is the special structure of the oral cavity. It has two sections - the pharynx and the esophagus, connecting to the