Scientific classification Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class:Agnatha

1. Scientific classification Kingdom:Animalia Phylum:Chordata Subphylum:Vertebrata Class:Agnatha

2. INTRODUCTION Agnatha - (Greek, "no jaws") is a class or superclass of jawless fish in the phylumChordata, subphylum Vertebrata. The group excludes all vertebrates with jaws, known as gnathostomes. as a whole are paraphyletic. The oldest fossil agnathans appeared in the Cambrian, and two groups still survive today .

3. -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. - 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 exothermic, with a cartilaginousskeleton, and the heart contains 2 chambers

4. Key feature of Agnatha Jaws are absent. Paired fins are generally absent. Early species had heavy bony scales and plates in their skin, but these are not present in living species. In most cases the skeleton is cartilaginous. The embryonic notochord persists in the adult. Seven or more paired gill pouches are present. The digestive system lacks a stomach.

5. OVERVIEW AND CLASSIFICATION • Vertebrates (subphylum Vertebrata) are generally classified into two groups: • 1.Agnatha (jawless vertebrates) - includes the modern day lampreys (Petromyzontiformes) and hagfish (Myxiniformes) as well as several extinct orders. 2. Gnathostomata (jawed vertebrates)- includes fish with hinged jaws and the tetrapods (amphibians, reptiles, birds, and mammals.

6. DESCRIPTION • All living and most extinct agnathans do not have an identifiable stomach or any paired appendages, although the hagfish and lampreys do have a tail and a caudal fin. • Some extinct agnathans reveal thick body plates. • The internal skeleton of the Agnatha is not bony but rather cartilaginous

7. -As characteristic of the class, hagfish and lampreys have a notochord that remains throughout life.-This notochord is the first primitive vertebral column. In the extant agnathans, fertilization and development are both external, and there is no parental care.-Although lampreys and hagfish are superficially similar, many of these similarities are probably shared primitive characteristics of ancient vertebrates. Thus, modern classifications tend to place hagfish into a separate group, with the lampreys (Hyperoartii) being more closely related to the jawed fishes.

8. 2 main types of fish in the agnatha class. 1. LAMPREY are of the order, Petromyzontiform. They are suckers and attach themselves to fish in order to parasitize off them. scaleless, eel-like, cartilaginous fish that have a round, jawless mouth which suctions onto the flesh of the fish they feed on. their fins are not paired, and they have one nostril and a third pineal eye on top of their head. they have 7 gills on each side

9. LAMPREYS LIFE CYCLE • Lampreys will lay their eggs in flowing water. • When the eggs hatch, the larvae drift down-stream to an area with a soft, but not muddy, bottom. • They dig into the bottom and form a burrow with their mouth just above the bottom. • A good portion of the lifespan of the animal is spent in this filter-feeding larval stage known as an ammocoete. As with most larvae, they do not yet have sex organs. • When the metamorphosis to adult occurs, the lamprey swims into the water. • The Sea Lamprey will search for a host to feed on blood before mating. Some Lamprey's do not eat as an adult. They mate and die in one to three weeks

10. Example of lampreys

11. 2. Hagfish Are of the order, Myxiniform. They are related to the slimefish.. Rather worm-like in appearance, the hagfish lack paired fins, only having a slight tail fin. They have no eyes and no scales. They also have rows of horny teeth on the tongue which rasp at the food. Surrounding the mouth is a ring of tentacles. Hagfish produce a great deal of slime

12. Example of a hagfish

13. Metabolism Agnathans are ectothermic or cold blooded, meaning they do not regulate their own body temperature. Agnathan metabolism is slow in cold water, and therefore do not have to eat as much. They have no distinct stomach, but rather a long gut, more or less homogenous throughout its length. Lampreys are parasitic, feeding off of other fish and mammals. They rely on a row of sharp teeth to shred their host. Fluids preventing clotting are injected into the host,causing the host to yield more blood. Hagfish are decomposers, eating mostly dead animals. They also use a sharp set of teeth to break down the animal. Agnathans feeding habits have limited their ability to advance evolutionarily. The fact that all Agnathan's teeth are not able to move up and down limit their possible food types. They have never been known to attack humans, without water they would die so when they are taken out of the water with their host they will release immediately.

14. Body covering The only modern Agnathan body covering is skin, with neither dermal or epidermal scales. The skin of hagfish has copious slime glands, the slime constituting their defence mechanism. Many extinct agnathans sported heavy dermal armour or small mineralized scales (see below).

15. Appendages Most agnathans, including all those living today have no paired appendages, although they do have a tail and a caudal fin. Some fossil agnathans, such as osteostracans, did have paired fins, a trait inherited in their jawed descendants

16. Skeleton The internal skeleton of the Agnatha is not bony but rather cartilaginous (made up of dense connective tissue). The somewhat rudimentary skull never ossifies and remains a chondrocranium throughout life. Also, Agnathans retain a notochord in adulthood, a characteristic distinctive of the class. This notochord is a cartilagious rod that forms the basis of the vertebral column in highter vertebrates

17. Reproduction Fertilization is external, as is development. There is no parental care. Not much is known about the hagfish reproductive process. It is believed that hagfish only have 30 eggs over a lifetime. Most species are hermaphrodites. There is very little of the larval stage that characterizes the lamprey. Lampreys can only reproduce once. After external fertilization, the lamprey's cloacas remain open, allowing a fungus to enter their intestines, killing them. Lampreys reproduce in freshwater river beds, and bury their eggs about two centimeters underground. Lampreys work in pairs buildings the egg nests. Lampreys go through four years of larval development before becoming adults. They also have a certain unusual form of reproduction.

18. Fossil agnathans Although a minor element of modern marine fauna, Agnatha were prominent among the early fish in the early Paleozoic. Two types of Early Cambrian animal apparently having fins, vertebrate musculature, and gills are known from the early Cambrian Maotianshanshales of China: Haikouichthys and Myllokunmingia. They have been tentatively assigned to Agnatha by Janvier. A third possible agnathid from the same region is Haikouella. A possible agnathid that has not been formally described was reported by Simonetti from the Middle Cambrian Burgess Shale of British Columbia. Many Ordovician, Silurian, and Devonian agnathans were armored with heavy bony-spiky plates.

19. Ostracoderms – first armored agnathans, precursors to the bony fish and hence to the tetrapods (including humans)—are known from the middle sOrdovician, and by the Late Silurian the agnathans had reached the high point of their evolution. Most of the ostraoderms, such as thelodonts, osteostracans, and galeaspids, were more closely related to the gnathostomes than to the surviving agnathans, known as cyclostomes.

20. Cyclostomes apparently split from other agnathans before the evolution of dentine and bone, which are present in many fossil agnathans, including conodonts. Agnathans declined in the Devonian and never recovered