APPENDIX 839 



PHYLUM 23. CHORDATA. 1 he chordates. Deuterostomes having at some stage of their 

 life a notochord; pharyngeal gill pouches; a single, dorsal, tubular 

 nerve cord. 

 Subphylum 1 . Urochordata. 1 he sea squirts. Notochord and nerve cord found only in 

 the larva. 

 CLASS 1. ASCIDIACEA. Sessile sea squirts, solitary or colonial. Molgula. 

 CLASS 2. THALIACEA. Pelagic sea squirts propelled by jets of water ejaculated 



by the contractions of the body wall. Salpa. 

 CLASS 3. LARVACEA. Pelagic, neotenic sea squirts retaining the larval tail as 

 a propulsive organ. Apfjendicularia. 

 Subphylum 2. Cephalochordata. The lancelets, fusiform chordates in which the noto- 

 chord extends the length of the bodv. Ainphioxus. 

 Subphylum 3. Vertebrate. The vertebrates, chordates with a cranium encasing a 

 brain; notochord generally replaced in adult by vertebrae. 

 CLASS 1. AGNATHA. Primitive, jawless vertebrates. 



t Ostracoderms. A collective name for four orders of ancient, heavily 

 armored fishes. Hemicyclaspis. 

 Order 5. Cyclostomata. Living, jawless fishes. The lampreys and hag- 

 fishes. The sea lamprey, Petromyzon. 

 t CLASS 2. PLACODERMI. Six orders of early jawed Hshes. The spiny shark, 

 Climatius. 

 CLASS 3. CHONDRICHTHYES. Fishes with cartilaginous skeletons. 



Subclass 1. Ei.ASMoiiRANcini. Cartilaginous fishes in which the gill slits 

 open independently at the body surface, 

 t Order 1. Cladoselachii. Primitive sharks with broad based fins. 

 Cladoselache. 

 Order 2. Selachii. Modern sharks. The dogfish, Squalus: whale shark, 



Rluucadon. 

 Order 3. Batoidea. Skates and rays. The common skate, Raja; devil- 

 fish, Manta; sawfish, Pristis. 

 Subclass 2. Hoi ocfpii all Abberant cartilaginous fishes. 

 Order 1. Chimaerae. The ratHsh, Cliiuiaera. 

 CLASS 4. OSTEiCHTHYES. Fishes with at least partly ossified skeletons; lungs 

 or swim bladder generally present. 

 Subclass 1. Actinoptfr^ cii. Bony fishes with rav fins. 



Superorder I. Cliotidrustei. Four orders of primitive ray-finned fishes. 

 The bichir, Polypterus; sturgeon, Scaphirhynchus: paddlefish, 

 Polyodon. 

 Superorder 2. Hulostei. Five orders of intermediate ray-finned fishes. 



The garpike, Lepisosteus; bowfin, Anna. 

 Superorder 3. Teleostei. Advanced ray-finned fishes. 



Order 1. Isospondyii. Primitive teleosts. The tarpon. Tarpon; her- 

 ring. Cltipea: salmon and trout, Sahno. 

 Order 2. Ostariophysi. Most fresh-water teleosts. such as the carp, cat- 

 fish, suckers and true minnows. The bullhead, Ameiurus. 

 Order 3. Apodes. The eels. The .American eel, Anguilla. 

 Order 4. Heteromi. Certain deep-sea fishes. 

 Order 5. Mesichthyes. Intermediate teleosts. The pike, Esox: killifish, 



Fundulus; stickleback, Gasterosteus: sea horse. Hippocampus. 

 Order 6. Acanthopterygii. Teleosts having spines in their fins. The 

 perch, Perca: simfish, Lepomis; bass, Micropterus; cod, Gadus; 

 halibut, Hippoglossus; and most other teleosts. 

 Subclass 2. Sarcopterygii. Bony fishes with fleshy fins and often internal 

 nostrils. 



