Chordates CHAPTER 15

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

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

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

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

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

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