Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
• Phylum Chordata • I. General characteristics – A. Notochord (Gr. Noto = back, L. chorda = cord) • 1. A skeletal rod • 2. All members have a notochord • 3. Primary purpose is to support, stiffen and assist as a skeletal axis • 4. Is not always hard calcified material, but can be of cartilage • 5. Usually dorsal to the organism • 6. Contains the main nerve cord in most cases. – B. Pharyngeal pouches and slits • 1. Perforated slitlike opening • 2. Present at some stage in life cycle, but may develop into another form. • 3. In lower chordates it becomes gills or filterfeeding apparatus. • 4. In tetrapod vertebrates (four footed), the pouches develop into Eustachian tubes, middle ear cavity, tonsils, and parathyroid glands. – The slits form into pharynx – C. Postanal tail • 1. Projects past the anus during some stages but disappears in some members. • 2. In vertebrates without tails the postanal tail becomes part of the vertebrate or dorsal nerve cord. – D. Muscles are segmented – E. Closed circulatory system • 1. Dorsal and ventral blood vessels – F. Complete and enclosed digestive system. – G. Endoskeleton • 1. Either bone or cartilage • II. Subphylums – A. Urochordata ex. tunicates • 1. 3000 species • 2. Marine • 3. Most are sessile with a few free living. • 4. Tunic present-calcified covering open at one end. • 5. Larval stage bears all chordate characteristics except the pharyngeal slits are not present • 6. Defense mechanisms-A jet of water is discharged. • 7. As adults they have incurrent and excurrent siphons for gas exchange and food getting. • 8. They are hermaphroditic or monoecious. – B. Cephalochordata: ex. amphioxus • 1. Slender and laterally flattened or compressed. • 2. About 5-7 cm in length • 3. Live in sandy bottoms of coastal water worldwide • 4. 25 species with 4 found in North America indigenously (naturally). • 5. Have all main characteristics of chordates at adulthood. • 6. Pharyngeal slits used for capturing food. • 7. Dioecious • 8. External fertilization – C. Vertebrata:(fish to human) • 1. Totally endoskeleton made up of living cells that grow with the body. • 2. Skeleton provides area for muscle attachment • 3. Skull and thoracic ribs protect major organs • 4. In agnathan and sharks endoskeleton is made up of cartilage • 5. Advanced nervous system including a Central nervous system (CNS) and brain • 6. Paired limbs – A. pelvic and pectoral appendages.