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

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: 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 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 Adult amphibians
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 Adult 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

51. Reproduction Some amphibians abandon their eggs after they are laid
Others incubate the young in their mouth, on their back, or even in their stomach!

52. Movement Amphibian larvae
Often move very much like fishes, wiggling their bodies and using a flattened tail for propulsion

53. Movement Adult amphibians
Most use their front and back legs to move in a variety of ways
Jump, climb, run, etc.

54. Response Nictitating Membrane:
Moveable transparent membrane in amphibians located inside the regular eyelid
Protects the surface of the eye from damage under water and keeps it moist on land

55. Response Tympanic Membrane Eardrum of amphibians Inside the skull
Vibrates in response to sound, allowing hearing

56. Groups of Amphibians Salamanders: Order Urodela
Long bodies and tails
Four legs
Carnivores
Frogs and Toads: Order Anura
Frogs: Long legs and lengthy jumpers
Toads: short legs and short hops
Adults lack tails
Caecilians: Order Apoda
Legless animals that live in water or burrow in moist soil or sediment

57. Ecology of Amphibians Have no feathers, fur or scales
Many are ideal for predators such as birds and mammals

58. Ecology of Amphibians
Amphibians have adaptations to protect themselves
Many have skin colors and markers that allow them to blend in with the environment
Some release toxins
Some are brightly colored as a warning to predators