Nonvertebrate Chordates, Fishes, and Amphibians

1. Biology I: Chapter 30 Nonvertebrate Chordates, Fishes, and Amphibians

2. CHORDATES

3. Chordates • Phylum Chordata • Fishes, amphibians, reptiles, birds and mammals • Four key characteristics: 1. Dorsal, hollow nerve cord 2. A notochord 3. Pharyngeal pouches 4. Tail that extends beyond the anus

4. Dorsal, Hollow Nerve Cord • Nerves branch from this cord at regular intervals • Nerves connect to internal organs, muscles and sense organs

5. Notochord • Long support rod • Runs through the body just below the nerve cord • Most chordates only have in the embryonic stage

6. Pharyngeal Pouches • Paired structures in the throat (pharynx) region • Fishes and amphibians: slits develop that connect the pharyngeal pouches to the outside of the body • The slits may then develop into gills that are used for gas exchange

7. Tail • All chordates have a tail that extends beyond the anus at some point in their lives • The tail can contain bone and muscles and is used in swimming by many aquatic species

8. Most Chordates are Vertebrates • More than 99% of all chordates are in the subphylum Vertebrata • Vertebrae: individual segments that make up the backbone; encloses and protects the spinal cord • Backbone is part of an endoskeleton, or internal skeleton

9. Nonvertebrate Chordates • The two groups • Soft-bodied marine organisms • Have the four key characteristics at some point in their lives • Tunicates • Filter feeders • Lancelets • Small, fish-like creatures

10. Fishes • Aquatic vertebrates that are characterized by: • Paired fins • Used for movement • Scales • Used for protection • Gills • Used for exchanging gases

11. Evolution of Fishes • Fishes were the first vertebrates to evolve • The evolution of jaws and the evolution of paired fins were important developments during the rise of fishes

12. The First Fishes • Jawless creatures whose bodies where armored with bony plates • Lived in the oceans during the late Cambrian Period, about 510 mya • Fishes kept this armored, jawless body plan for 100 million years

13. The Age of Fishes • Ordovician and Silurian Periods: 505-410 mya, fishes underwent a major adaptive radiation • Devonian Period: “Age of Fishes” • Some were jawless with little armor • Ancestors of modern hagfishes and lampreys • Others were armored and ultimately became extinct about 360 mya

14. The Arrival of Jaws • Other ancient fishes kept their bony armor and possessed a feeding adaptation that would revolutionize vertebrate evolution: JAWS • Jawless fishes • Limited to eating small particles of food that they filter out of the water or suck up like a vacuum cleaner • Jaws can hold teeth and muscles • Much wider variety of food • Defend themselves by biting

15. The Arrival of Paired Fins • More control of body movement • Fin tails and powerful muscles gave greater thrust when swimming • Enabled fishes to move in new and varied patterns • This enabled fishes to use their jaws in complex ways

16. The Rise of Modern Fishes • Although the early jawed fishes soon disappeared, they left behind two major groups that continued to evolve and still survive today • Ancestors of modern sharks and rays: skeletons made of resilient cartilage • Group that evolved skeletons made of true bone

17. Form and Function in Fishes • Adaptations to aquatic life include: • Various modes of feeding • Specialized structures for gas exchange • Paired fins for locomotion

18. Feeding • Herbivores, carnivores, parasites, filter feeders, detritus feeders • A single fish may exhibit several modes of feeding (carp: eat what is available) while others are very specialized (barracuda: carnivore) • Pyloric ceca: finger-like pouches found in many species of fish that secrete digestive enzymes to help digest food

19. Respiration • Most fishes exchange gases using gills located on either side of the pharynx • The gills are made up of feathery filaments • Lampreys and sharks have several gill openings on the side of the body • A number of fishes, such as the lungfish, have an adaptation that allows them to survive in oxygen-poor water or in areas where bodies of water often dry up

20. Respiration

21. Circulation • Closed circulatory systems with a heart that pumps blood around the body in a single loop • Heart consists of 4 parts: • Sinus venosus: thin-walled sac that collects blood from the fish’s veins • Atrium: a large muscular chamber that serves as a one-way compartment for blood • Ventricle: thick-walled muscular chamber; pumping portion of the heart • Bulbus arteriosus: connects to a large blood vessel called the aorta, which moves blood to the fish’s gills

22. Circulation

23. Excretion • Most fishes rid themselves of nitrogenous wastes in the form of ammonia • Gills, kidneys • Saltwater fishes • Lose water by osmosis: kidneys return as much water to the body as possible • Freshwater fishes • Gain water by osmosis: kidneys pump out plenty of dilute urine

24. Response • Well-developed nervous systems organized around a brain • Cerebrum: area of the brain responsible for all voluntary activities of the body • Cerebellum: region of the brain that coordinates body movements • Medulla oblongata: area of the brain that controls the functioning of many internal organs

25. Response • Lateral line system: sensitive receptor system that enables fish to detect gentle currents and vibrations in the water (the 6th sense)

26. Movement • Most move by alternately contracting paired sets of muscles on either side of the backbone • Because their body tissues are more dense than the water they swim in, sinking is an issue for fishes • Swim bladder: gas-filled organ found in many bony fishes that adjusts their buoyancy

27. Reproduction • Oviparous: term used to refer to animals whose eggs hatch outside the mother’s body • Ovoviviparous: term used to refer to animals whose young are born alive after developing in eggs inside the mother’s body • Viviparous: term used to refer to animals that bear live young that are nourished directly by the mother’s body as they develop

28. Groups of Fishes • Over 24,000 living species that are extremely diverse • Jawless fishes • Cartilaginous fishes • Bony fishes

29. Jawless Fishes • Have no true teeth or jaws • Skeletons are made of fibers and cartilage • Lack vertebrae; keep notochords as adults • Two main classes: • Lamprey • Hagfishes

30. Sharks and Their Relatives • Class Chondrichthyes • Sharks, rays, skates, • Also: sawfishes and chimaeras • Cartilage, not bone

31. 350 Living Species • Curved tails • Torpedo-shaped bodies • Pointed snouts • Mouth underneath • Enormous number of teeth • Always exceptions!

32. Bony Fishes • Class Osteichthyes • Skeletons made of hard, calcified tissue: bone • Ray-finned fishes • Rays or spines that support the fins • Only 7 living species of bony fish are not ray-finned • Lobe-finned fishes

33. Ecology of Fishes • Anadromous: fishes that spend most of their lives in the ocean but migrate to fresh water to breed • Examples: lampreys, sturgeons, and salmon • Catadromous: fishes that spend most of their lives in fresh water but migrate to the ocean to breed • Example: European eel, American eel

34. AMPHIBIANS

35. Amphibian • Have survived for hundreds of millions of years • The only modern descendants • of an ancient group that gave rise to all other land vertebrates • Amphibian means “double life”…live in both water and on land

36. Amphibian • Vertebrate • Lives in the water as a larva and on land as an adult (with some exceptions) • Breathes with lungs as an adult • Has moist skin that contains mucus glands • Lacks scales and claws

37. Evolution of Amphibians • The first amphibians to climb onto land probably resembled lobe-finned fishes similar to the modern coelacanth • The amphibian had legs, appearing about 360 mya

38. Evolution of Amphibians • Early amphibians evolved several adaptations that helped them live at least part of their lives out of water: • Bones in the limbs and limb girdles became stronger for more efficient movement • Lungs and breathing tubes enabled them to breathe air • The sternum formed a bony shield to support and protect internal organs, esp. the lungs

39. Evolution of Amphibians • Soon after they appeared, amphibians underwent a major adaptive radiation • Some were huge: Eogyrinus was about 5 meters long! • Amphibians became the dominant form of animal life in the warm, swampy fern forests about 360-286 mya • Climate changes caused many of the swamps to disappear • Most amphibians became extinct

40. Evolution of Amphibians • Only three orders of small amphibians survive today: • Frogs and toads • Salamanders • Caecilians

41. Form and Function in Amphibians • Although the class Amphibia is relatively small, it is diverse enough to make it difficult to identify a typical species • We will focus on the structures found in frogs…

43. Feeding • Tadpoles • Filter feeders or herbivores that graze on algae • Eat almost constantly • Adult amphibians • Almost entirely carnivorous • Mouth esophagus  stomach  small intestines  large intestines  cloaca

44. Respiration • Larval amphibians • Gas is exchanged through the skin and gills • Adult amphibians • Lungs and skin

45. Circulation • Double loop • 3 chambered heart First Loop • Carries oxygen-poor blood: heart  lungs and skin • Takes oxygen-rich blood: lungs and skin  heart

46. Circulation • Second Loop • Transports oxygen-rich blood: heart  rest of the body • Transports oxygen-poor blood: body  heart

47. Circulation

48. Excretion • Amphibians have kidneys that filter wastes from the blood • Urine: The excretory product of the kidneys • Urine travels through tubes called ureters into the cloaca • Urine is passes outside or temporarily stored in a bladder above the cloaca

49. Reproduction • Eggs do not have shells and tend to dry out if they are not kept moist • Most species lay eggs in the water • The male fertilizes them externally • In a few species (most salamander), eggs are fertilized internally

50. Reproduction • The male climbs onto the female’s back • The female releases the eggs that are then fertilized • The eggs are in a transparent jelly, useful for attaching the eggs to underwater plants and that provides nourishment to the growing cells