Tunicates are very common marine animals with interesting features. These animals spend their entire adult life attached to a solid surface, and are closely related to vertebrates. In their early free-swimming larval stage tunicates resemble a tadpole with a nervous cord called a notochord. A notochord is actually the primitive beginnings of a backbone and can be found in the early developmental stages of human embryos. Once ready to become an adult the larvae will attach to a solid surface head first and begin its transformation. The adults look completely different than the larval stage, and are called tunicates because of a firm protective tunic that surrounds the animal. Adult tunicates are filter feeders and have two siphons – the oral siphon brings fresh seawater into the tunicate where plankton and oxygen can be retained, and the second siphon (atrial siphon) expels waste products. Some of these animals have been valuable to medicine as several anti-tumor compounds have been discovered within their tissues.