1. Chordates
CHAPTER 15

3. The Chordates: Characteristics
Structural Plan
Name chordata comes from the notochord
Rodlike, semirigid tissue enclosed in a sheath
In most cases, extends the length of body lying between the gut and the nervous system
Mainly serves to stiffen the body, providing skeletal scaffolding for the attachment of swimming muscles
Hallmark chordate characteristics
Dorsal, tubular nerve cord
Notochord
Pharyngeal slits
Postanal tail
Endostyle

5. Subphylum Urochordata: Tunicata
Diversity
Approximately 3000 species of tunicates identified
Occur in all seas and at all depth
Most are sessile as adults although a few are free-living
Tunic is a tough, nonliving test that surrounds them and contains cellulose
In most species, only the larval form bears all the chordate hallmarks
Adults lose many of these characters

7. Subphylum Urochordata: Tunicata
During adult metamorphosis
Notochord and tail disappear
Dorsal nerve cord is reduced
Urochordata is divided into 3 classes
Ascidia
Thalacia
Appendicularia

12. Subphylum Cephalochordata
Diversity
Lancelets or amphioxus
Slender, laterally flattened, translucent animals about 5–7 cm long
Live in sandy bottoms of coastal waters around the world
About 25 species of amphioxus are described
5 occur in North American coastal waters

14. Subphylum Vertebrate (Craniata)
Endoskeleton of living hagfishes, lampreys, sharks and their kin, and even some “bony” fishes, such as sturgeons, mostly composed of cartilage
Structural strength of bone is superior to cartilage
Makes it ideal for muscle attachment in areas of high mechanical stress
Perhaps bone evolved, in part, as a means of mineral regulation
Phosphorus and calcium are used for many physiological processes
In particularly high demand in organisms with high metabolic rates

15. Subphylum Vertebrate (Craniata)
Some of the most primitive fishes, including Ostracoderms and placoderms were partly covered in a bony, dermal armor
Modified in later fishes as scales
Most vertebrates are protected with keratinized structures derived from the epidermis
Reptilian scales, hair, feathers, claws, and horns
Physiology
Modifications of digestive, respiratory, circulatory, and excretory systems to meet increased metabolic demand