Phylum Chordata Subphylum Vertebrata Class Agnatha No Jaws

Phylum Chordata Subphylum Vertebrata Class Agnatha “No Jaws”

Class Agnatha • All species have circular mouth – Lampreys, hagfish, slime eels

Characteristics • Body is long, slender – no paired fins • No scales – smooth skin with protective coating of mucous • Circular mouth – anterior & ventral – Buccal funnel lined with conical teeth for grasping

Characteristics • Notochord – protective flexible cartilaginous endoskeleton • Heart – 2 chambered – Atrium & ventricle – aorta leads to gills • Closed circulatory system – red & white blood cells • Gills paired in pouches off pharynx – Gill slits (7 or more, paired)

Characteristics • Excretory – kidneys • Digestive – complete, but without stomach • Nervous system – well developed – Dorsal nerve cord with brain – 8 to 10 cranial nerves – Spinal cord branches into nerve net

Characteristics • Sensory reception – Olfactory sac – smell/taste reception – Eyes & ears – Extent of development varies by species – Lateral line – similar to sharks, aids in equilibrium, senses vibrations in water

Characteristics • Reproduction – ovaries & testes present in an individual, HOWEVER: – Gonads of only one sex function, making them dioecious – Oviparous with external fertilization – Most are anadromous (live in salt water, but return to freshwater to spawn) • Aquatic & marine species • Often parasitic, harmful to commercial fishing