1. Their bodies are slender, elongated and without paired fins. 13-100 cm long.
2. They look like eel or bine fish.
3. The body is strong in nature and free of scales.
4. They have a notochord and neural tube in their spinal cord.
5. The mouth has suction cups and keratinized (horned) teeth.
6. They have seven pairs of florets.
7. The nasal sac does not open into the oral cavity.
8. Although marine, they come to freshwater to spawn and die within days of hatching.
9. They are known as lampreys.
10. The digestive system does not have a stomach and the intestine has spiral membranes. 11. Excretion occurs. The life cycle of the amocete larvae is as follows.
12. Joint appendages and exoskeleton are absent. There are dorsal fins and caudal fins.
[KEY WORDS TO REMEMBER CHARACTERISTICS: bine, scaleless, chub, keratin, floret, lamprey, amocite]
Examples: Petromyzon (Petromyzon marinus), Lampetra (Lampetra tridentatus).