Chapter 23: Question 3

Name five hallmarks shared by all chordates, and explain the function of each.

The five hallmarks shared by all chordates are the notochord, dorsal tubular nerve cord, pharyngeal pouches or slits, endostyle, and postanal tail. The functions of each of these are..

1. Notochord a flexible, rodlike structure, that extends the length of the body. It is the first part of the endoskeleton to appear in the embryo. The notochord is an axis for muscle attachment, and because it can bend without shortening, it permits undulatory movements of the body.

2. Dorsal Tubular Nerve Cord ventral to the alimentary canal and is solid, but in chordates the single cord is dorsal to the alimentary canal and its a hollow tube. The hollow cord is produced in the embryo by infolding of ectodermal cells on the dorsal side of the body above the notochord.

3. Pharyngeal Pouches and Slits openings that lead from the pharyngeal cavity to the outside. They are formed by inpocketing of the outside ectoderm and evagination, or outpocketing of the endodermal lining of the pharynx.

4. Endostyle or Thyroid Gland found in all chordates, but no other animals. The endostyle in the pharyngeal floor, secretes mucus that traps small food particles brought into the pharyngeal cavity.

5. Postanal Tail provides the motility that larval tunicates and amphioxus need for their free-swimming existance. It is a structure added to the body behind the end of the digestive tract, and it clearly has evolved specifically for propulsion in water.
