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 The oldest fossil agnathans appeared in the Cambrian, and two groups still survive today.
The lampreys and the hagfish, with about 100 species in total.
In addition to the absence of jaws, modern agnathans are characterized by absence of paired fins the presence of a notochord both in larvae and adults and seven or more paired gill pouches.
 They have a light sensitive pineal eye.
All living and most extinct Agnatha do not have an identifiable stomach or any appendages.
Fertilization and development are both external.
The Agnatha are exothermic, with a cartilaginous skeleton, and the heart contains 2 chambers.
Agnatha is divded into two groups given below :
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1. Lamprey
2. Hagfish