Introduction to Vertebrates

1. Introduction to Vertebrates Chapter 39 Fishes

2. Introduction to Vertebrates • Vertebrates are members of the subphylum Vertebrata, within the phylum Chordata. All Chordates share the following characteristics. • Notochord • Dorsal hollow nerve cord • Pharyngeal pouches • Post-anal tail

3. Introduction to Vertebrates Vertebrates are distinguished from chordates by: • Vertebrae - bones or cartilage that surround the dorsal nerve cord and form the spine. • A cranium - a skull that protects the brain • An endoskeleton - an internal skeleton made of bone or cartilage

4. Introduction to Vertebrates • Myxini - hagfishes • Cephalaspidomorphi - lampreys • Chondrichthyes - sharks, rays, skates, and ratfishes • Actinopterygii - ray-finned fishes • Sarcopterygii - lobe-finned fishes • Amphibia - frogs, toads, salamanders, and caecilians • Reptilia - lizards, snakes, and turtles • Aves - birds • Mammalia - mammals

5. Introduction to Vertebrates

6. Vertebrate Evolution • Most biologists think that vertebrates originated about 560 million years ago. • The first fish were jawless.

7. Vertebrate Evolution • About 450 million years ago, the first fishes with jaws and paired fins appeared. • Jaws are thought to have evolved from the first pair of gill arches, the skeletal elements that support the pharynx.

9. Vertebrate Evolution The advantages to jaws and paired fins: • Paired fins increased fishes’ stability and maneuverability in water • Jaws allowed fishes to seize and manipulate prey

10. Jawless and Cartilaginous Fishes:Fish Adaptations Fish have several adaptations that make them well suited to life in water: • Streamlined body plan - allows fish to move rapidly in water • Adaptations for buoyancy - stored gases or lipids help maintain vertical position in water • Efficient respiration - internal gills exchange gases efficiently

11. Jawless and Cartilaginous Fishes:Fish Adaptations Adaptations for salt and water homeostasis - • The concentration of solutes in a fish’s body usually differs from the concentration of solutes in the water. • Fish have adaptations to maintain ion and water homeostasis.

12. Jawless and Cartilaginous Fishes:Fish Adaptations Sensory adaptations - Fish have a variety of organs that allow them to sense their environment. • Sight: fish eyes are similar to eyes of land vertebrates • Sound: fish have internal ears sensitive to sound

13. Jawless and Cartilaginous Fishes:Fish Adaptations Chemoreception: the ability to detect chemicals in the environment includes the senses of smell and taste.

14. Jawless and Cartilaginous Fishes:Fish Adaptations • Fish have nostrils and tastebuds. Tastebuds may be located in their mouths, on their lips, fins, and skin, and on whisker-like organs called barbels.

15. Jawless and Cartilaginous Fishes:Fish Adaptations Unique senses: • Lateral line: the lateral line is a system of canals in the skin that allow fish to sense vibration in the water • Ampulae of Lorenzini: cartilaginous fishes have sense organs called ampulae of Lorenzini that can detect weak electrical fields • Electroreception and Magnetoreception: some fish have the ability to detect electrical and magnetic fields

16. Lateral Line in Fishes

17. Jawless Fishes Only two classes of jawless fishes are alive today: • Hagfishes (class Myxini) Hagfishes are bottom-dwellers that feed on dead and dying fish.

18. Jawless Fishes • Lampreys (class Cephalaspidomorphi) Lampreys can be free-living or parasitic. Parasitic lampreys attach themselves to their host with disc-shaped mouths and feed on the blood and body fluids of other fishes. All lampreys breed in fresh water. Fertilization occurs outside the body - external fertilization.

19. Cartilaginous Fishes All cartilaginous fishes: • belong to the class Chondrichthyes. • have skeletons made of cartilage - a flexible lightweight material made of cells surrounded by tough fibers of protein.

20. Cartilaginous Fishes All cartilaginous fishes: • have skin covered with placoid scales - small, toothlike spines that feel like sandpaper. • Placoid scales probably reduce turbulence and increase swimming efficiency.

21. Cartilaginous FishesSharks: • Sharks have torpedo shaped bodies that reduce turbulence when swimming, called a fusiform body shape. • Some sharks are filter feeders, and have slender projections on the inner surface of their gills, called gill rakers, that filter the water.

22. Cartilaginous FishesSharks: • The mouth of a typical shark has 6 to 20 rows of teeth. When a tooth breaks or wears down, a replacement moves forward. One shark may use more than 20,000 teeth over its lifetime.

23. Cartilaginous FishesRays and Skates: • Rays and skates have flattened bodies with paired wing-like pectoral fins and, in some species, whip-like tails. • Rays have diamond- or disk-shaped bodies. Most skates have triangular bodies.

24. Cartilaginous FishesRays and Skates: • Rays and skates are primarily bottom dwellers, and most feed on mollusks and crustaceans.

25. Cartilaginous FishesRatfishes: • Ratfishes are a small group of strange looking fish that have a flap of skin covering their gill slits. • Ratfishes have long, rat-like tails and feed on crustaceans and mollusks.

26. Adaptations in Cartilaginous Fishes: • Some sharks push water through their mouth and over their gills by swimming. • Most cartilaginous fish pump water over their gills by expanding and contracting their mouth cavity and pharynx.

27. Adaptations in Cartilaginous Fishes: • When lying on the bottom, rays and skates draw water in to their gills through spiracles, two large openings on the top of the head, behind the eyes.

28. Sharks convert ammonia to urea in their bodies. • Sharks retain large amounts of urea in their bodies to raise the concentration of solutes in their bodies to the same level as that found in sea water.

29. Sharks still tend to take up sodium and chloride ions. • The rectal gland removes excess sodium and chloride ions from the body.

30. Cartilaginous fishes maintain their position in the water in two ways. • The caudal and pectoral fins generate lift, or upward force, as the fish swims. • Many cartilaginous fish store large amounts of lipids, usually in the liver. Lipids are less dense than water.

31. Reproduction in Cartilaginous Fishes: • Fertilization occurs inside the body of the female, called internal fertilization. • Some cartilaginous fish lay eggs.

32. Reproduction in Cartilaginous Fishes: • The eggs of many species develop within the female’s body. • In some species, the mother nourishes the developing young while they are in her body.

33. Bony Fishes: Characteristics of Bony Fishes Bony fishes have three key features: • Bone - the skeletons of most bony fishes contain bone. • Lungs or swim bladder - early bony fishes had lungs, organs which exchange gas between the air and blood. Most bony fishes today have a swim bladder, a gas-filed sac that is used to control buoyancy. • Scales - scales protect the body of a bony fish and reduce friction when swimming.

34. Swim Bladder in Bony Fish

35. Bony Fishes: Characteristics of Bony Fishes There are two main groups of bony fishes: • Lobe-finned fishes - have fleshy fins supported by a series of bone. • Ray-finned fishes - have fins that are supported by long, segmented, flexible bony elements called rays.

36. Bony Fishes:External Anatomy • Operculum: Most bony fish have an operculum, a hard plate that opens at the rear and covers and protects the gills. • Fins: The fins of most fish are supported by rays or spines. Rays are flexible, spines are rigid.

37. Bony Fishes:External Anatomy • Skin: The skin of most bony fish are covered with scales. Scales are thin, round disks of a bonelike material that grow from pockets in the skin and overlap like shingles.

38. Yellow Perch

39. Bony Fishes:Internal Anatomy Digestive system ---- • Food passes from the mouth into the pharynx, through the esophagus, to the stomach. • From the stomach food passes into the intestine, where nutrients are absorbed. • Undigested material is eliminated through the anus.

40. Bony Fishes:Internal Anatomy Circulatory system: • The circulatory system of a fish delivers oxygen and nutrients to the cells of the body. • The circulatory system consists of a heart, bloodvessels, and blood.

41. Internal Structure

42. Bony Fishes:Internal Anatomy Circulatory system: • The heart pumps blood through arteries to small, thin-walled vessels called capillaries, in the gills. • From the gills, the blood travels to the body tissues, where nutrients and wastes are exchanged. • The blood returns to the heart through veins.

43. Bony Fishes:Internal Anatomy Circulatory system The heart of a bony fish has two chambers in a row, as shown below. Blood from the body enters the sinus venosus, moves into the atrium, then into the ventricle. From the ventricle it enters the conus arteriosus, and then goes to the gills.

45. Bony Fishes:Internal Anatomy Respiratory system • Fish use gills for gas exchange. • Water flows across the gill filaments in a direction opposite to blood flow, called countercurrent flow.

46. Bony Fishes:Internal Anatomy • Countercurrent flow allows more oxygen to diffuse into the blood than would be possible if blood and water flowed in the same direction.

48. Bony Fishes:Internal Anatomy Excretory system • The kidneys filter chemical wastes from the blood to form urine, a solution containing ammonia, ions such as salts, and water. • The kidneys help regulate the ion and water balance in fish.

49. Bony Fishes:Internal Anatomy • The gills also allow wastes to diffuse from the blood into the water and help regulate ion and water balance in fish.

50. Bony Fishes:Internal Anatomy Swim bladder • The swim bladder is a thin-walled sac in the abdominal cavity that contains a mixture of oxygen, carbon dioxide, and nitrogen obtained from the bloodstream. • Swim bladders evolved from balloonlike lungs, which ancestral bony fishes may have used to supplement the oxygen absorbed by the gills.