Superclass Agnatha Classes Myxini and Cephalaspidomorphi about 84 species lack a jaw paired fins no scales relationships among agnathans is uncertain.

Presentation on theme: "Superclass Agnatha Classes Myxini and Cephalaspidomorphi about 84 species lack a jaw paired fins no scales relationships among agnathans is uncertain."— Presentation transcript:

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3 Superclass Agnatha Classes Myxini and Cephalaspidomorphi about 84 species lack a jaw paired fins no scales relationships among agnathans is uncertain

4 Class Myxini (hagfishes) teeth on tongue naked skin no paired appendages fibrous and cartilagenous skeleton 2 chambered heart (ventricle, atrium) pronephritic kidney

5 no stomach nervous system no cerebellum eyes degenerate 10 pairs of cranial nerves no larval stage- direct development Class Myxini (hagfishes)

6 Class Cephalaspidomorphi = Petromyzontides (Lampreys) no jaws; –mouth with circular sucker like structure with lots of teeth Pineal eye; third eye for orientation

7 persistent notochord cartilaginous skeleton two median fins, no paired appendages 2 chambered heart –blood with specialized cells- leucocytes, nucleated erythrocytes Class Cephalaspidomorphi = Petromyzontides (Lampreys)

8 gills as adults mesonephritic kidney brain with 10 cranial nerves; small cerebellum present poikilothermic (cold blooded) Class Cephalaspidomorphi (Lampreys)

9 Life cycle Parasitic on fishes external fertilization metamorphosis Class Cephalaspidomorphi (Lampreys)

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11 Lamprey larva hagfish have direct development; lampreys with ammocoetes larva