Chordata All Chordates have 4 unique and very specific characteristics: Notochord- Supportive rod extending the dorsal length of the body. Pharyngeal Slits- Series of slits in this region between the digestive tract and exterior. (filter feeding) Dorsal nerve cord- Nerve cord running along longitudinal axis. Postanal tail- Tail extending beyond anal opening.

Section 1: Early Chordates & Fish Subphylum Urochordata (tail + cord) Sea Squirts (Tunicates) Sessile as adults Respond to external stimuli but no complex nervous response

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Monoecious- Adult contains both male and female gametes. Self- fertilization does occur but is rare.

Subphylum Cephalochordata (head + cord) Lancelets ~45 species Up to 5cm long Distinct features include 4 characteristics of a chordate.

Spends a majority of it’s time burrowed in sand, filter feeding. Dioecious- male and female gametes on separate organisms

Cephalochordata Urochordata Vertebrata Endoskeleton 4 chordata traits

Subphylum Vertebrata Development bony vertebrae to replace the notochord. Increased fossil record of this group More distinct cephalization Anterior skull develops to enclose brain.

Jawless fish were among the first vertebrates. ~500 mya Developed into “true fish” and eventually into terrestrial vertebrates.

Class Osteichthyes (bone + fish) Any fish that has at least some bone ~20,000 species Freshwater or marine

Locomotion Fish have a streamline body with scales Excrete fluids that reduce friction as they move through the water.

Gas exchange & Respiration Gills-aquatic respiratory organ found in fish Ram Ventilation-movement of water across the gills by swimming with mouth open.

Maintaining the proper balance of water and Osmoregulation Maintaining the proper balance of water and ions (electrolytes) in their tissues.

Freshwater- Environment has lower salt concentration. Water wants to enter tissue. These fish never drink. Only while eating. Obtain salts(ions) from food Produce high quantities of dilute urine. Marine- Environment has high salt concentration Water wants to leave tissue. Drink water Excrete salts through tissue Produce concentrated urine