The Annelida, also known as the ringworm, are a very large phylum that include over 20,000 species of worms that include earthworms and leeches. They can be found in both marine and terrestrial environments. Sensors are mostly single celled and detect light, pressure waves, chemicals, and touch. Many Annelida's have little eyes that are responsible for detecting light and forming images. The brain in the Annelida is formed by rings of nerves around the pharynx and contain ganglia that function as a control center. The nervous system consists of nerve chords that form a ladder-like structure throughout he body. Nerve trunks include giant axons that allow them to transmit signals throughout the body very fast. The Annelida can react to touch very fast by shortening the length of their bodies. Some Annelida's have palps that help with consumption and feeling the environment around them. Annelida's also contain organs responsible for equilibrium in the body called statocysts.