1. Comparing Invertebrates
Chapter 29

2. Invertebrate Evolution
Chapter 29-1

3. Origins of Invertebrates
29-1 Invertebrate Evolution
Origins of Invertebrates
Early animals were flat, soft bodied organisms that lived on the bottom of shallow seas.
Segmented with bilateral symmetry.
NO cell specialization.
Recently scientists discovered microscopic fossils that are million years old.
Seem to be developing embryos of early multi-cellular organisms. 3

4. The First Multicellular Animals
29-1 Invertebrate Evolution
The First Multicellular Animals
Ediacaran Fossils found in China
610 to 570 Million Years old
They are the ancestors of today’s multicellular animals

5. The First Multicellular Animals
29-1 Invertebrate Evolution
The First Multicellular Animals
The fossils:
were flat and plate shaped
were segmented
had bilateral symmetry
lived on the bottom of shallow seas
were made of soft tissues
absorbed nutrients from the surrounding water

6. Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
Many features of modern invertebrates evolved during the Cambrian period such as:
tissues and organs
patterns of early development
body symmetry
cephalization
segmentation
formation of three germ layers and a coelom

7. Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
Invertebrate Evolutionary Relationships
This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals.

8. Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
Roundworms
Flatworms
Cnidarians
This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals. Labels indicate the evolution of major features such as radial symmetry.
Sponges
Unicellular ancestor

9. Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals.

10. Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals.

11. Invertebrate Phylogeny
29-1 Invertebrate Evolution
Invertebrate Phylogeny
Invertebrate Evolutionary Relationships
This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals.

12. Evolutionary Trends Specialized cells, Tissues, and Organs
29-1 Invertebrate Evolution
Evolutionary Trends
Specialized cells, Tissues, and Organs
Sponges - 1st with specialized cells
Jelly fish - 1st with muscle tissue
Flatworms - 1st with organs
Body Symmetry
Asymmetrical (no symmetry) – Sponges only
Radial – Jellyfish and Echinoderms
Bilateral – Flatworms, Roundworms, Annelids, arthropods, and Mollusks 12

13. 29-1 Invertebrate Evolution
Evolutionary Trends
Cnidarians and echinoderms exhibit radial symmetry where parts extend from the center of the body.
Radial symmetry
Planes of symmetry

14. 29-1 Invertebrate Evolution
Evolutionary Trends
Worms, mollusks, and arthropods exhibit bilateral symmetry, or have mirror-image left and right sides.
Bilateral symmetry

15. Cephalization Evolutionary Trends
29-1 Invertebrate Evolution
Evolutionary Trends
Cephalization
Cephalization is the concentration of sense organs and nerve cells in the front of the body.
Invertebrates with cephalization can respond to the environment in more sophisticated ways than can simpler invertebrates.
None: Sponges
Nerve Net: Cnidarians
Ganglia: Worms, Clams, Echinoderms
Brains: Cephalopod Mollusks, Arthropods 15

16. Segmentation Evolutionary Trends
29-1 Invertebrate Evolution
Evolutionary Trends
Segmentation
Over the course of evolution, different segments in invertebrates have often become specialized for specific functions.
Segmentation allows an animal to increase its size with minimal new genetic material.

17. Coelom Formation Evolutionary Trends Acoelomate
29-1 Invertebrate Evolution
Evolutionary Trends
Coelom Formation 
Flatworms are acoelomates. This means they have no coelom, or body cavity, that forms between the germ layers.
Ectoderm
Mesoderm
Endoderm
Acoelomates do not have a coelom, or body cavity, between their body wall and digestive cavity.
Digestive cavity
Acoelomate

18. 29-1 Invertebrate Evolution
Evolutionary Trends
Pseudocoelomates have a body cavity lined partially with mesoderm.
Pseudocoelom
Pseudocoelomates have body cavities that are partially lined with tissues from mesoderm.
Digestive tract
Pseudocoelomate

19. 29-1 Invertebrate Evolution
Evolutionary Trends
Most complex animal phyla have a true coelom that is lined completely with tissue derived from mesoderm.
Coelom
Most complex animal phyla are coelomates, meaning that they have a true coelom that is lined completely with tissues from mesoderm.
Digestive tract
Coelomate

20. 29-1 Invertebrate Evolution
Evolutionary Trends 20

21. Embryological Development
29-1 Invertebrate Evolution
Evolutionary Trends
Embryological Development  
In most invertebrates, the zygote divides to form a blastula—a hollow ball of cells.

22. 29-1 Invertebrate Evolution
Evolutionary Trends
In most worms and arthropods, nerve cells are arranged in structures called ganglia.
In more complex invertebrates, nerve cells form an organ called a brain.

23. Evolutionary Trends 29-1 Invertebrate Evolution
This table shows the major characteristics of the main groups of invertebrates. Germ layers, body symmetry, cephalization, and development of a coelom are more common in complex invertebrates than in simple ones. Mollusks, for example, have all of these features, but sponges have none of them.

24. Evolutionary Trends 29-1 Invertebrate Evolution
This table shows the major characteristics of the main groups of invertebrates. Germ layers, body symmetry, cephalization, and development of a coelom are more common in complex invertebrates than in simple ones. Mollusks, for example, have all of these features, but sponges have none of them.

25. Invertebrate Form & Function
Chapter 29-2

26. The End

27. 29-2 Form and Function in Invertebrates
Feeding and Digestion
Intracellular: Food digested by cells and passed around by diffusion. (ex: sea anemone)
Extracellular: food
broken down in
cavity and then
absorbed. (ex: earthworm) 27

28. Feeding and Digestion Feeding and Digestion
29-2 Form and Function in Invertebrates
Feeding and Digestion
Feeding and Digestion
The simplest animals break down food primarily through intracellular digestion. More complex animals use extracellular digestion.

29. 29-2 Form and Function in Invertebrates
Feeding and Digestion
When food is digested inside cells, this process is known as intracellular digestion.
Sponges use intracellular digestion.

30. 29-2 Form and Function in Invertebrates
Feeding and Digestion
In extracellular digestion, food is broken down outside the cells in a digestive cavity or tract and then absorbed into the body.
Mollusks, annelids, arthropods, and echinoderms rely almost entirely on extracellular digestion.
Flatworms and cnidarians use both intracellular and extracellular digestion.

31. 29-2 Form and Function in Invertebrates
Feeding and Digestion
Cnidarians and most flatworms ingest food and expel wastes through a single opening.
Food is digested in a cavity through both extracellular and intracellular means.

32. Feeding and Digestion Cnidarian Flatworm
29-2 Form and Function in Invertebrates
Feeding and Digestion
Mouth/anus
Gastrovascular cavity
Cnidarians and flatworms have a digestive system with only one opening. In more complex animals, the digestive system has two openings. In addition, the digestive organs have become more specialized.
Digestive cavity
Cnidarian
Pharynx
Mouth/anus
Flatworm

33. 29-2 Form and Function in Invertebrates
Feeding and Digestion
In more-complex animals, food enters the mouth and wastes leave through the anus.
A one-way digestive tract often has specialized regions.

34. Feeding and Digestion Annelid Arthropod
29-2 Form and Function in Invertebrates
Feeding and
Digestion
Intestine
Gizzard
Crop
Pharynx
Annelid
Mouth
Anus
Crop
Pharynx
Cnidarians and flatworms have a digestive system with only one opening. In more complex animals, the digestive system has two openings. In addition, the digestive organs have become more specialized.
Anus
Arthropod
Mouth
Stomach and digestive glands
Rectum
Intestine

35. Respiration All respiratory systems have two basic requirements:
29-2 Form and Function in Invertebrates
Respiration
All respiratory systems have two basic requirements:
a large surface area that is in contact with the air or water
the respiratory surfaces must be moist for diffusion to occur

36. Respiration Aquatic invertebrates: Require moist respiratory surfaces
29-2 Form and Function in Invertebrates
Respiration
Aquatic invertebrates:
Require moist respiratory
surfaces
Some through the pores
of the skin
Some through gills (large
feathery structure rich in
blood vessels)
Large surface area provides for greater absorption of oxygen. 36

37. Respiration Aquatic Invertebrates
29-2 Form and Function in Invertebrates
Respiration
Aquatic Invertebrates
Gills are feathery structures that expose a large surface area to the water.
Invertebrates have a variety of respiratory structures. Clams and other aquatic mollusks have gills.

38. Respiration Terrestrial Invertebrates: Covered by water or mucus
29-2 Form and Function in Invertebrates
Respiration
Book Lungs
Terrestrial Invertebrates:
Covered by water or mucus
inside the body.
Book lungs – spiders
Spiracles - other insects
Spiracles 38

39. Respiration Terrestrial Invertebrates
29-2 Form and Function in Invertebrates
Respiration
Terrestrial Invertebrates
Grasshoppers and other insects have spiracles and tracheal tubes.
Invertebrates have a variety of respiratory structures. Grasshoppers and other insects have spiracles and tracheal tubes. All respiratory organs have large, moist surface areas in contact with air or water.

40. 29-2 Form and Function in Invertebrates
Circulation
Most complex animals have one or more hearts to move blood through their bodies and either an open or closed circulatory system

41. Circulation Open – blood partially contained in vessels
29-2 Form and Function in Invertebrates
Circulation
Open – blood partially contained in vessels
Closed – blood forced through vessels 41

42. Circulation Open Circulatory Systems
29-2 Form and Function in Invertebrates
Circulation
Open Circulatory Systems
In an open circulatory system, blood is only partially contained within a system of blood vessels.
One or more hearts or heartlike organs pump blood through blood vessels into a system of sinuses, or spongy cavities.
The blood makes its way back to the heart.

43. 29-2 Form and Function in Invertebrates
Circulation
Open circulatory systems are characteristic of arthropods and most mollusks.
Most complex animals have one or more hearts to move fluid through their bodies in either an open or a closed circulatory system. An insect has an open circulatory system in which blood leaves blood vessels and then moves through sinuses, or body cavities.

44. Circulation Closed Circulatory Systems
29-2 Form and Function in Invertebrates
Circulation
Closed Circulatory Systems
In a closed circulatory system, a heart or heartlike organ forces blood through vessels that extend throughout the body.
Materials reach body tissues by diffusing across the walls of the blood vessels.
Closed circulatory systems are characteristic of larger, more active animals.

45. 29-2 Form and Function in Invertebrates
Circulation
Among the invertebrates, closed circulatory systems are found in annelids and some mollusks.
Heartlike structure
Small vessels in tissue
Most complex animals have one or more hearts to move fluid through their bodies in either an open or a closed circulatory system. An annelid has a closed circulatory system in which blood stays in blood vessels as it moves through the body.
Blood vessels
Annelid: Closed Circulatory System
Heartlike structures

46. 29-2 Form and Function in Invertebrates
Excretion
Most animals have an excretory system that rids the body of metabolic wastes while controlling the amount of water in the tissues.
In aquatic invertebrates, ammonia diffuses from their body tissues into the surrounding water.

47. Excretion Aquatic invertebrates:
29-2 Form and Function in Invertebrates
Excretion
Aquatic invertebrates:
Diffusion: aquatic mollusks, sponges, and jelly fish
Mollusk examples
Flame cells: flatworms 47

48. Excretion Terrestrial Invertebrates Convert ammonia to urea
29-2 Form and Function in Invertebrates
Excretion
Terrestrial Invertebrates
Convert ammonia to urea
to conserve water
Nephridia: Terrestrial mollusks
and earthworms
Malpighian tubules: insects
and spiders 48

49. 29-2 Form and Function in Invertebrates
Excretion
Flatworms use a network of flame cells to eliminate excess water.
Flame Cells
Excretory tubules
Flame Cell
Most animals dispose of wastes through excretory systems. Excretory systems also control an organism’s water levels. Flatworms excrete ammonia directly into the water and use flame cells to remove excess water.
Excretory tubule
Flatworm

50. 29-2 Form and Function in Invertebrates
Excretion
In annelids and mollusks, urine forms in tubelike structures called nephridia.
Nephrostome
Excretory pore
Most animals dispose of wastes through excretory systems. Excretory systems also control an organism’s water levels. Annelids use nephridia to convert ammonia into urea and to concentrate it in urine.
Annelid
Nephridia

51. 29-2 Form and Function in Invertebrates
Excretion
Fluid enters the nephridia through openings called nephrostomes.
Urine leaves the body through excretory pores.
Urine is highly concentrated, so little water is lost.

52. 29-2 Form and Function in Invertebrates
Some insects and arachnids have Malpighian tubules, saclike organs that convert ammonia into uric acid.
Excretion
Digestive tract
Most animals dispose of wastes through excretory systems. Excretory systems also control an organism’s water levels. Some arthropods have Malpighian tubules, which convert ammonia into uric acid. Uric acid is eliminated from the body in a paste.
Malpighian tubules
Arthropod

53. 29-2 Form and Function in Invertebrates
Excretion
Uric acid and digestive wastes combine to form a thick paste that leaves the body through the rectum.
The paste helps to reduce water loss.

54. 29-2 Form and Function in Invertebrates
Response
Invertebrates show three trends in the evolution of the nervous system: centralization, cephalization, and specialization.

55. Response Nerve Nets: individual nerve cells in a net-like formation.
29-2 Form and Function in Invertebrates
Nerve Nets: individual nerve cells in a net-like formation.
Ganglia: Centralized nerve cells connected to the nerve net.
Brain: Highly organized ganglia connected to nerve net.
Specialization: when cells have a special job (ex: eyespots, eyes, chemical receptors, etc.) 55

56. Response Centralization and Cephalization
29-2 Form and Function in Invertebrates
Response
Centralization and Cephalization
Cephalization is the concentration of nerve tissue and organs in one end of the body.

57. Response Specialization
29-2 Form and Function in Invertebrates
Response
Specialization
The more complex an animal’s nervous system is, the more developed its sense organs tend to be.
Complex animals may have a variety of specialized sense organs that detect light, sound, chemicals, movement, and electricity.

58. 29-2 Form and Function in Invertebrates
Response
Cnidarians have nerve nets which consist of individual nerve cells that form a netlike arrangement throughout the animal’s body.
Nerve cells
Invertebrate nervous systems have different degrees of centralization, cephalization, and specialization. Cnidarians have a simple nerve net.
Cnidarian

59. 29-2 Form and Function in Invertebrates
Response
In flatworms and roundworms, the nerve cells are more centralized.
There are a few clumps of nerve tissue, or ganglia, in the head.
Ganglia
Invertebrate nervous systems have different degrees of centralization, cephalization, and specialization. Flatworms, whose nervous systems are more centralized, have small ganglia in their heads.
Flatworm

60. Response
29-2 Form and Function in Invertebrates
Brain
In cephalopod mollusks and arthropods, ganglia are organized into a brain.
Ganglia
Arthropod
Brain
Invertebrate nervous systems have different degrees of centralization, cephalization, and specialization. Arthropods and cephalopod mollusks have a centralized brain and specialized sensory organs.
Mollusk

61. 29-2 Form and Function in Invertebrates
Movement and Support
Most animals use muscles to move, breathe, pump blood, and perform other life functions.
In most animals, muscles work together with some sort of skeletal system that provides firm support.

62. 29-2 Form and Function in Invertebrates
Movement and Support
Hydrostatic skeleton: muscles surround a fluid-filled body cavity.
Exoskeleton: Arthropods: Hard body covering made of chitin.
Endoskeleton: Echinoderms: internal structural support.
Hydrostatic: as the muscle contracts it pushed the fluid in another direction causing change in shape. 62

63. Movement and Support Hydrostatic Skeleton
29-2 Form and Function in Invertebrates
Movement and Support
Hydrostatic Skeleton
Circular muscles contracted
Water
The three main types of invertebrate skeletons are hydrostatic skeletons, exoskeletons, and endoskeletons. In animals with hydrostatic skeletons, muscles contract against a fluid-filled body cavity.
Longitudinal muscles contracted
Water

64. Movement and Support Exoskeleton
29-2 Form and Function in Invertebrates
Movement and Support
Exoskeleton
Flexed joint
The three main types of invertebrate skeletons are hydrostatic skeletons, exoskeletons, and endoskeletons. In animals with hydrostatic skeletons, muscles contract against a fluid-filled body cavity. In animals with exoskeletons, the muscles pull against the insides of the exoskeleton.
Extended joint

65. Movement and Support Endoskeleton
29-2 Form and Function in Invertebrates
Movement and Support
Endoskeleton
The three main types of invertebrate skeletons are hydrostatic skeletons, exoskeletons, and endoskeletons. Echinoderms and some sponges have endoskeletons. Photo Credit: ©Lawrence Naylor/Photo Researchers, Inc.
Skeletal plates
Tube foot

66. Sexual & Asexual Reproduction
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction
Sexual reproduction maintains genetic diversity in a population.
Asexual reproduction allows animals to reproduce rapidly and take advantage of favorable conditions in the environment.

67. Sexual & Asexual Reproduction
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction
Sexual reproduction is the production of offspring from the fusion of gametes.
Male and female gametes join to create a zygote.
The zygote grows through mitosis and develops into a multicellular animal.

68. Sexual & Asexual Reproduction
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction
In most animals, each individual is a single sex. (male of female)
The individual produces either sperm or eggs.
Some animals are hermaphrodites—individuals that produce both sperm and eggs.

69. Sexual & Asexual Reproduction
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction
In external fertilization, eggs are fertilized outside the female’s body.
In internal fertilization, eggs are fertilized inside the female’s body.

70. Sexual & Asexual Reproduction
29-2 Form and Function in Invertebrates
Sexual & Asexual Reproduction
The offspring of asexual reproduction grow into multicellular organisms by mitosis of diploid cells.
Some animals reproduce asexually through budding or by dividing in two.

71. 29-2 Form and Function in Invertebrates
Reproduction
Most invertebrate reproduce sexually to increase genetic diversity.
BUT….in certain conditions they will reproduce asexually in order to ensure continuation of species. 71