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The Chordates - Phylum: Chordata - Chordates are distinguished from all invertebrates by the presence of 4 anatomical structures. - The structures can be present at any point of the animal’s life. - Notochord - A flexible, longitudinal rod located between the digestive tube and the nerve cord. - Provides skeletal support. - In invertebrates, it persists throughout the life of the animal. - - - - In vertebrates, a supportive skeleton develops and the notochord degenerates. Dorsal, Hollow Nerve Cord - The nerve cord develops into the central nervous system (brain & spinal cord). - Invertebrates have a nerve cord, but it is solid and usually ventrally located. - The nerve cord is ectoderm in origin. Pharyngeal Gill Slits - Present in all embryos. - Persist in aquatic animals for respiration and or filter feeding. Postanal Tail - Present in all embryos. - Turns into a tail for many vertebrates. - Some vertebrates reabsorb the tail as development continues (frogs, humans). - Figure 34.2 Chordate characteristics - Subphylum: Urochordata (tunicates) - Subphylum: Cephalochordata (lancelets) - Subphylum: Vertebrata (the vertebrates) All have a closed circulatory system. The neural crest forms some bones and the cranium. - It is a collection of embryonic cells. Class: Agnatha - Jawless fish. - All are extinct except for lampreys and hagfishes. - - Class: Placodermi - The placoderms. - All are extinct. - Had thick, tough plates on skin. - Were the first jawed fishes. - Class: Chondrichthyes - Sharks, skates, chimaeras and rays. - All have cartilage instead of bone. - 750 extant species - Well developed lateral line system. - They show all 3 types of development/birth: - Oviparous: lay eggs that hatch outside of the mother’s body. - Ovoviviparous: fertilized eggs develop inside the body. Nutrition comes from yolk. Eggs hatch inside mother and “live birth” to a well-developed young occurs. - Viviparous: true “live birth”. Young is nourished by a placenta-like structure. - Class: Osteichthyes - Bony fish. - About 33,000 species. - Have a swim bladder (filled with air). - Have a 2 chambered heart. - Class: Amphibia - Includes frogs, salamanders. - 4,000 species. - Still tied to the water for reproduction. - Most require a moist skin surface for respiration. - 3 chambered heart (2 atria, 1 ventricle) - Class Reptilia: - Snakes, lizards, turtles, crocodiles. - Have become less dependent of water for reproduction. - The movement on land is due to the evolution of the amniotic egg. - Scales made of keratin prevents desiccation. - 7,000 species. - All are ectotherms (“cold blooded”). - All have a 3 chambered heart except for crocodiles (4 chambered). - Class: Aves - The birds. - 8,500 species - Share reptile characteristics of scales on legs and reproduction with an amniotic egg. - 4 chambered heart with “double respiration” - Anatomy is modified for flight: - Hollow bones - Lightweight feathers - Only 1 ovary - No copulatory organ in males. - Class: Mammalia - The mammals. - All have 4-chambered heart. - - - Have fur (hair), most give live birth and young develop in a placenta. There are 3 major groups: 1. Monotremes : egg layers - 2. Marsupials: pouched - 3. Eutherians: placentals Some common orders: - Monotremata (hedgehog) - Marsupialia (kangaroos, koalas) - Carnivora (dogs, seals, weasels, raccoons, walrus, cats) - Cetacea (dolphins, whales) - Artiodactyla Perissodactyla Chiroptera Lagomorpha Primates Rodentia Proboscidea Sirenia (sheep, giraffes, cows, pigs, [even # of toes]) (rhinos, horses, zebras, [odd # of toes]) (bats) (rabbits) (monkeys, humans) (capybara, beavers, prairie dogs) (elephant) (manatee)