THE ANIMAL KINGDOM 3 1 



Urochorda. Notochord limited to tail-region. Body-wall covered 

 with cellulose sac. Hemichorda and urochorda together are often called 

 protochordates. Appendicularia. Ascidia. 



CEPH.A.LOCHORDA. Xotochord in head, trunk, and tail throughout 

 life. Metameric. Amphioxus. 



Vertebrata. Chordates with brain case and vertebrae. Squalus. 



Classes of Vertebrates (Craniota) 



1. Cyclostomata. Without paired appendages or biting jaw. 

 Hermaphroditic. Petromyzon, myxine, bdellostoma. 



2. OsTRACODERMi, fossil monorhine fishes related to the cyclostomes. 



3. Pisces. With paired appendages and movable lower jaw. Skin 

 scalv. Permanent gills. Fishes are subdi\'ided into five sub-classes: 



Elasmobranchii, with naked gills. Skeleton cartilaginous. Sharks, 

 skates, and rays. 



Crossopterygii, fossil forms related to the ganoids. 



Ganoidei, with operculum. Cartilage skeleton largely replaced by 

 bone. Garpike, sturgeon. 



Teleostei, with operculum and bony skeleton. Common bony fishes. 



Dipnoi, with gills and one or two lungs. 



All following are Tetrapods. 



4. Amphibia. Living forms are without scales and usually have lungs. 

 Toed appendages instead of fins. 



The Stegocephala are a group of fossil amphibia. 

 Fishes and Amphibia grouped together as Ichthyopsida. 

 All to this point are Anamnia. All that follow are Amniota, having the 

 embryo protected by an amnion. 



5. Reptilia. Adults scaly. Lungs only. Aortic arch on both sides. 

 The Theromorpha are fossil reptiles. 



6. A\t:s. Feathered. Modern forms toothless. Aortic arch on 

 the right side only. 



Reptiles and birds grouped together as Sauropsida. 



7. Mammalia. With mammary glands and hair. 



Sub-Classes of Mammals 



1. Monotremes. Egg-laying mammals. 



2. Marsupials. Pouched mammals. 



3. Placentalia. Mammals with a placenta. 



Orders of Placentalia 



1. Insectivora. Insect eaters. 



2. Xenarthra. Toothless or teeth without enamel. 



3. Rodentia. Incisors specialized for gnawing. 



