Agnatha
Agnatha (Greek, "no jaws") is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. The group excludes all vertebrates with jaws, known as gnathostomes.
The oldest fossil agnathans appeared in the Cambrian, and one group still survives today: the lampreys In addition to the absence of jaws, modern agnathans are characterised by absence of paired fins; the presence of a notochord, both in larvae and adults; and seven or more paired gill pouches. There is a light sensitive pineal eye (homologous to the pineal gland in mammals). All living and most extinct Agnatha do not have an identifiable stomach or any appendages. Fertilization and development are both external. There is no parental care in the Agnatha class. The Agnatha are ectothermic or cold blooded, with a cartilaginous skeleton, and the heart contains 2 chambers.
The oldest fossil agnathans appeared in the Cambrian, and one group still survives today: the lampreys In addition to the absence of jaws, modern agnathans are characterised by absence of paired fins; the presence of a notochord, both in larvae and adults; and seven or more paired gill pouches. There is a light sensitive pineal eye (homologous to the pineal gland in mammals). All living and most extinct Agnatha do not have an identifiable stomach or any appendages. Fertilization and development are both external. There is no parental care in the Agnatha class. The Agnatha are ectothermic or cold blooded, with a cartilaginous skeleton, and the heart contains 2 chambers.