1. Phylum Chordata: The Chordates

2. Characteristics Common to all Chordates
Notochord – a supportive rod that extends most of the length of the animal (think vertebrae); allows for muscle attachment
Bilaterally symmetrical
Pharyngeal Slits or Pouches – think gills
Dorsal Hollow Nerve Cord – think spinal cord and nervous system
Tail
Presence of thyroid gland
Complete digestive tract
Heart

3. Our Chordate Ancestors: Tunicates (Subphylum Urochordata)
Tunicates, also called sea squirts, have all the characteristics of a chordate but lack a backbone, so they are invertebrates.
They are usually found in marine environments, but a few species are found in fresh water.
Some species of tunicates are colonial while others are solitary.
Tunicates go through a free swimming larval stage before becoming sessile. They attach to the seafloor through extensions called stolons.
Monoecious

4. Tunicate Life Cycle

5. Our Other Chordate Ancestors: The Lancelets (Subphylum Cephalochordata)
Lancelets are usually about 1 in. (2.5 cm) long, with transparent bodies tapered at both ends.
Lancelets are filter feeders and live in shallow marine waters; they can swim through water or wet sand, but are usually found buried in the sand with only the mouth end projecting.
A ventral blood vessel carries the colorless blood; there is no heart.
Dioecious

6. Lancelet Actual Size

7. Fig. 23.p469a

8. Fig. 23.p469b

9. Fig. 23.p472a

10. Fig. 23.p472c