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5/30/2013 PHYLUM CHORDATA 1 5/30/2013 4 Main Characteristics 1.Notochord - Firm but flexible tube that functions in support - Present at least during embryonic development (but often replaced by a backbone) 2.Gill slits - Present at least during embryonic development - Develop into gills or lungs in vertebrates 3. Dorsal nerve chord - Becomes brain and spinal chord in vertebrates 4. Post anal tail 2 5/30/2013 Lancelet: ***note - most posses a backbone (Tunicates and Lancelets are an exception to this rule) 3 5/30/2013 Other characteristics often shared by vertebrates: • Endoskeleton - made of cartilage or bone and can support a larger body • Bilateral symmetry • High degree of cephalization - well developed head and brain protected by cranium • Closed circulatory system - heart with 2, 3 or 4 chambers • Only phylum to have bones • Tube digestive system 4 5/30/2013 The Phylum Chordata Includes: 1. Subphylum Cephalochordata (=lancelets) 2. Subphylum Urochordata (= tunicates) 3. Subphylum vertebrata: • Class Agnatha - jawless fish • Class Amphibia • Class Aves – birds • Class Chondrichthyes - cartilaginous fish • Class Osteichthyes - bony fish • Class Reptilia • Class Mammalia 5 5/30/2013 AMPHIBIANS 6 5/30/2013 Amphibians • A.k.a. – “two lives” • Most primitive of terrestrial vertebrates • Fossil records say they are similar to fish • May live on land or in water, but MUST have moist or aquatic environment to reproduce • Includes frogs, toads, salamanders and caecilians 7 5/30/2013 Appendages • Adapted to where they spend their time: • Powerful hind limbs for leaping • (frogs and toads) • Sticky disks for grasping branches • (frogs) • Webs between toes for swimming • (frogs) • Paddle like tail for swimming • (newts) 8 5/30/2013 Feeding • Adults feed primarily on insects • Larvae (tadpoles) feed primarily on plant matter • Digestive system • mouth, esophagus, stomach, small intestine, large intestine, cloaca • Accessory glands • pancreas (enzymes) • liver (bile) 9 5/30/2013 Circulation • Double looped with a 3 chambered heart • 2 atria (receive blood) • 1 ventricle (pumps blood out of heart) • Larvae have a single loop and 2 chambered heart 10 5/30/2013 Respiration • Lungs - internal air sacs lined with membranes that stay moist even if outside environment is dry • Gills - external (unlike fish) so that gas exchange occurs as water flows over them • Can also occur through the skin and linings of the mouth (this means their skin must stay moist) 11 5/30/2013 Reproduction • External fertilization • Require moist or aquatic environment • Young hatch into aquatic larvae or tadpoles • Only a few species care for their young • Metamorphosis • A change in structure from larvae to adult • Often accompanied with a change in habitat 12 5/30/2013 13 5/30/2013 Other Characteristics • Poison glands • Found on some frogs and can be very toxic • On toads, “warts” are actually poison glands under the skin • Eyes can see in both water and air covered by nictitating membrane • Tympanic membrane detects sounds waves (hearing) 14 5/30/2013 1. Class Urodela • Ex. salamanders • Visible tail • Body with two pairs of legs • Smooth moist skin • Larvae - have gills, live in streams, lakes, rivers or ponds • Adults - most have lungs and live on land 15 5/30/2013 2. Class Anura • Without a tail (as adults) • Frogs • Have smooth moist skin • Longer legs, tapered bodies • Live in or near water • Toads • Dry, bumpy skin more resistant to drying • Only return to the water to reproduce 16 5/30/2013 3. Class Apoda • No legs • Ex. Caecillians • • • • Smooth skin, small eyes (but nearly blind) and worm like body Body folds look like segments Burrow through soil Average about 30 cm 17 5/30/2013 FISH 18 5/30/2013 Class Agnatha • No jaws • Most primitive fish - paired fins are absent so they are poor swimmers • Bottom dwellers or parasitic • Body is smooth, without scales and cylindrical • Skeleton made of cartilage • 7 or more paired gill pouches • Ex. hagfish and lamprey 19 5/30/2013 Class Chondrichthyes • Cartilage fish (skeleton made of cartilage) • Ex. sharks and rays • Hinged jaw • Body scales = placoid scales • Teeth are modified scales (can have 6-20 rows that continually replenish) 20 5/30/2013 Class Chondrichthyes Continued… • Paired fins - rigid, provide balance and lift while swimming • No swim bladder, instead they have an oily liver that gives buoyancy and they sink if they don’t swim • Must swim to move water across their gills or they will suffocate • Have good sense of smell • Electroreceptors- allow them to sense weak electrical charges made by muscle contractions in prey • Lateral line system - fluid filled canal with sensory receptors to detect pressure or vibration in the H2O 21 5/30/2013 Class Osteichthyes • Bony fish • Ex. salmon, goldfish, tuna • Hinged jaw with real teeth • Air bladder • used to raise or lower fish in water • in some species used as a very primitive lung • Cycloid scales point posterior and are covered by mucous… good for insulation, protection and waterproofing 22 5/30/2013 Class Osteichthyes Continued… • 4 pairs of gills, covered by operculum • Kidney helps regulate salts • Lateral line - detects vibrations • Inner ear connected to swim bladder for hearing • Heart consists of 2 chambers 23 5/30/2013 24 5/30/2013 Types of Bony Fish • Lobe finned fish - only one known living species, believed to be the first vertebrates to move out of water • Lungfish - have lungs as well as gills and an eel like body, some species can live out of water for up to 4 years • Ray-finned fish - fins made of thin membranes supported by bony rays for steering, breaking, etc 25