Agnatha Characteristics PDF
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This document describes the general characteristics of agnathans, a group of jawless vertebrates. It covers their features, including their lack of jaws, unique feeding mechanisms, and reproductive strategies. It also details their evolutionary history and their place within the broader context of vertebrate evolution.
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# General characteristics of Agnatha **Intro:** Agnatha (Greek, "No Jaws") is a superclass of Jawless fish in the phylum Chordata, sub-phylum Vertebrata, consisting of both present cyclostomes and extinct conodonts and ostracoderms) species. - The group of vertebrates with Jaws is known as gnathos...
# General characteristics of Agnatha **Intro:** Agnatha (Greek, "No Jaws") is a superclass of Jawless fish in the phylum Chordata, sub-phylum Vertebrata, consisting of both present cyclostomes and extinct conodonts and ostracoderms) species. - The group of vertebrates with Jaws is known as gnathostomes. - The oldest fossils Agathas appeared in the Cambrian. - Today, the lampreys and hagfish still survive and two groups were prominent among the early fish in the early Paleozoic. ## Characteristics Features of Agnatha: 1. In addition to the absence of Jaws, modern agnathans are characterized by absence of paired fins. 2. Presence of a notochord both in larvae and adults. They are only known living animals that have a skull but not a vertebral column. 3. Seven or more paired gill pouches. 4. Lampreys have a light sensitive pineal eye, homologous to the pineal gland in mammals. 5. All living and most extinct Agnatha do not have an identifiable stomach. 6. Alimentary canal: They have no distinct stomach, but rather a long gut, more or less homogenous throughout its length. 7. Nutrition: Lampreys feed on other fish and mammals. They rely on a row of sharp teeth to shred their host. 8. Hagfish are "scavengers", eating mostly dead animals. They also use a sharp set of teeth to break down the animals. 9. Body covering: In modern Agnathas, the body covering is skin, with neither dermal or epidermal scales. The skin of hagfish has copious slime glands. 10. Appendages: Almost all Agnathas, including all extant agnathas, have no paired appendages, although most have a dorsal fin. 11. Reproduction: Fertilization in lampreys is external. There is no known parental care. It is believed that hagfish only have 30 eggs over a lifetime. 12. Agnatha are ectothermic or cold-blooded, with a cartilaginous skeleton, and the heart contains 2 chambers.
