Organisms within the class Agnatha are jawless fish, and are probably the earliest of vertebrates. Most agnathans have a skeleton made of cartilage and seven or more paired gill pockets. They have a light sensitive pineal eye - a third eye in front of the pineal gland - and fertilization of eggs takes place outside the body.
jawless fishes (lampreys)
Lampreys are typically anadromous, and have been used for food since ancient times. Overfishing has hugely impacted this species and reduced stock in areas in Asia. Lampreys use something called an oral disk and rasping tongue to grasp prey, rasp hole in body, and suck out the tissues and fluids within the animals. The larvae are known as ammocoetes, and are also filter feeders.