Differences between Agnatha and Gnathostomata

S.N. Agnata Gnathostomata 1. The mouth is circular without jaws. The mouth is provided with jaws. 2. Paired appendages are missing. There are paired appendages, they can be fins or limbs. 3. The notochord is persistent. The notochord is usually replaced by a vertebral column. 4. The vertebral column is not developed or is represented by imperfect neural arches over the notochord. The spine is fully developed. 5. There are 8 to 10 pairs of cranial nerves. There are between 10 and 12 pairs of cranial nerves. 6. There is only one median nostril and one olfactory sac. There are paired nasal passages and olfactory sacs. 7. The inner ear has 1-2 semicircular canals. The inner ear has 3 semicircular canals. 8. The gonad is single and has no gonoduct. The gonads are paired and have gonoducts. 9. There is no organized pancreas or spleen. The pancreas and spleen appear as different organs. 10. The dorsal and ventral roots of the spinal nerves may or may not unite. The dorsal and ventral roots of the spinal nerves always join together. 11. They are poikilothermic. They can be poikilothermic or homeothermic.