1. Copyright Pearson Prentice Hall
Biology
Copyright Pearson Prentice Hall

2. 29-2 Form and Function in Invertebrates
Photo Credit: ©Brandon Cole/Visuals Unlimited
Copyright Pearson Prentice Hall

3. Copyright Pearson Prentice Hall
How do different invertebrate phyla carry out life functions?
Copyright Pearson Prentice Hall

4. Copyright Pearson Prentice Hall
Feeding and Digestion
Feeding and Digestion
The simplest animals break down food primarily through intracellular digestion. More complex animals use extracellular digestion.
Copyright Pearson Prentice Hall

5. Copyright Pearson Prentice Hall
Feeding and Digestion
When food is digested inside cells, this process is known as intracellular digestion.
Sponges use intracellular digestion.
Copyright Pearson Prentice Hall

6. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

7. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

8. Copyright Pearson Prentice Hall
Feeding and Digestion
Invertebrate Digestive Systems
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
Copyright Pearson Prentice Hall

9. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

10. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

11. Copyright Pearson Prentice Hall
Respiration
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
Copyright Pearson Prentice Hall

12. Copyright Pearson Prentice Hall
Respiration
Aquatic Invertebrates
Many animals respire through their skin.
Aquatic mollusks, arthropods, and many annelids exchange gases through gills.
Copyright Pearson Prentice Hall

13. Copyright Pearson Prentice Hall
Respiration
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.
Copyright Pearson Prentice Hall

14. Copyright Pearson Prentice Hall
Respiration
Terrestrial Invertebrates
Terrestrial invertebrates have several types of respiratory surfaces.
Many spiders have book lungs.
Copyright Pearson Prentice Hall

15. Copyright Pearson Prentice Hall
Respiration
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.
Copyright Pearson Prentice Hall

16. Copyright Pearson Prentice Hall
Circulation
Circulation
Most complex animals have one or more hearts to move blood through their bodies and either an open or closed circulatory system.
Copyright Pearson Prentice Hall

17. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

18. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

19. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

20. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

21. Copyright Pearson Prentice Hall
Excretion
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.
Copyright Pearson Prentice Hall

22. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

23. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

24. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

25. Copyright Pearson Prentice Hall
Excretion
Some insects and arachnids have Malpighian tubules, saclike organs that convert ammonia into uric acid.
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
Copyright Pearson Prentice Hall

26. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

27. Copyright Pearson Prentice Hall
Response
Response
Invertebrates show three trends in the evolution of the nervous system: centralization, cephalization, and specialization.
Copyright Pearson Prentice Hall

28. Copyright Pearson Prentice Hall
Response
Centralization and Cephalization
Cephalization is the concentration of nerve tissue and organs in one end of the body.
Copyright Pearson Prentice Hall

29. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

30. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

31. Copyright Pearson Prentice Hall
Response
In cephalopod mollusks and arthropods, ganglia are organized into a brain.
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
Copyright Pearson Prentice Hall

32. Copyright Pearson Prentice Hall
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.
Copyright Pearson Prentice Hall

33. Copyright Pearson Prentice Hall
Movement and Support
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.
Copyright Pearson Prentice Hall

34. Copyright Pearson Prentice Hall
Movement and Support
Invertebrates have one of three main kinds of skeletal systems: hydrostatic skeletons, exoskeletons, or endoskeletons.
Copyright Pearson Prentice Hall

35. Copyright Pearson Prentice Hall
Movement and Support
Hydrostatic Skeletons
In a hydrostatic skeleton, muscles surround a fluid-filled body cavity that supports the muscles.
When the muscles contract, they push against fluid in the body cavity, causing the body to change shape.
Annelids and certain cnidarians, have hydrostatic skeletons.
Copyright Pearson Prentice Hall

36. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

37. Copyright Pearson Prentice Hall
Movement and Support
Exoskeletons
An exoskeleton, or external skeleton, is a hard body covering made of chitin.
Arthropods have exoskeletons.
Arthropods move by using muscles that are attached to the inside of the exoskeleton.
Copyright Pearson Prentice Hall

38. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

39. Copyright Pearson Prentice Hall
Movement and Support
Endoskeletons
An endoskeleton is a structural support located inside the body.
Sea stars and other echinoderms have an endoskeleton. Vertebrates also have endoskeletons.
Copyright Pearson Prentice Hall

40. Copyright Pearson Prentice Hall
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
Copyright Pearson Prentice Hall

41. Sexual and Asexual Reproduction
Most invertebrates reproduce sexually during at least part of their life cycle. Depending on environmental conditions, however, many invertebrates may also reproduce asexually.
Copyright Pearson Prentice Hall

42. Sexual and 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.
Copyright Pearson Prentice Hall

43. Sexual and 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.
Copyright Pearson Prentice Hall

44. Sexual and Asexual Reproduction
In most animals, each individual is a single sex.
The individual produces either sperm or eggs.
Some animals are hermaphrodites—individuals that produce both sperm and eggs.
Copyright Pearson Prentice Hall

45. Sexual and Asexual Reproduction
In external fertilization, eggs are fertilized outside the female’s body.
In internal fertilization, eggs are fertilized inside the female’s body.
Copyright Pearson Prentice Hall

46. Sexual and 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.
Copyright Pearson Prentice Hall

47. Copyright Pearson Prentice Hall
29-2
Copyright Pearson Prentice Hall

48. Copyright Pearson Prentice Hall
29-2
Flatworms eliminate excess water using a network of
flame cells.
Malpighian tubules.
nephridia.
madrepores.
Copyright Pearson Prentice Hall

49. Copyright Pearson Prentice Hall
29-2
A hydrostatic skeleton is found in the
annelids.
echinoderms.
arthropods.
insects.
Copyright Pearson Prentice Hall

50. Copyright Pearson Prentice Hall
29-2
Complex animals break down food using
intracellular digestion.
extracellular digestion.
intracellular digestion and extracellular digestion.
digestion outside of the body.
Copyright Pearson Prentice Hall

51. Copyright Pearson Prentice Hall
29-2
Which structures are involved in gas exchange in one or more groups of invertebrates?
ganglia, brain, and nerve cells
gills, book lung, skin, and tracheal tubes
nephridia, flame cells, and nephrostomes
pharynx, crop, and intestine
Copyright Pearson Prentice Hall

52. Copyright Pearson Prentice Hall
29-2
Which groups have only one entrance and exit point to the digestive system?
annelids and echinoderms
arthropods and roundworms
mollusks and sponges
flatworms and cnidarians
Copyright Pearson Prentice Hall

53. END OF SECTION