1. 26-1 Introduction to the Animal Kingdom
Photo Credit: Fred McConnaughey/Photo Researchers, Inc.
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What Is an Animal?
What Is an Animal?
Animals are multicellular, eukaryotic heterotrophs whose cells lack cell walls.
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What Is an Animal?
Animals have the following types of tissues:
epithelial
muscular
connective
nervous
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What Is an Animal?
Epithelial tissues cover body surfaces.
Muscle tissue cells contain proteins that enable them to contract, moving parts of animals’ bodies.
Connective tissues support an animal’s body and connect its parts.
Nervous tissue contains nerve cells, which carry information throughout the body.
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What Is an Animal?
Invertebrates make up 95% of all animal species.
Invertebrates do not have a backbone, or vertebral column.
They include sea stars, worms, jellyfishes, and insects.
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What Is an Animal?
The other 5% of animals are vertebrates.
Vertebrates have a backbone.
Vertebrates include fishes, amphibians, reptiles, birds, and mammals.
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7. What Animals Do to Survive
Animals carry out the following essential functions:
feeding
respiration
circulation
excretion
response
movement
reproduction
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8. What Animals Do to Survive
Feeding
Herbivores eat plants.
Carnivores eat other animals.
Omnivores feed on both plants and animals.
Detritivores feed on decaying plant and animal material.
Filter feeders are aquatic animals that strain tiny floating organisms from water.
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9. What Animals Do to Survive
Respiration
Whether they live in water or on land, all animals respire—they take in oxygen and give off carbon dioxide.
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10. What Animals Do to Survive
Circulation
Animals transport oxygen, nutrient molecules, and waste products among all their cells through either simple diffusion or some kind of circulatory system.
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11. What Animals Do to Survive
Excretion
Ammonia is a waste product of cells and a poisonous substance.
Most animals have an excretory system that eliminates ammonia quickly or converts it into a less toxic substance that is removed from the body.
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12. What Animals Do to Survive
Response
Animals respond to events in their environment using specialized cells, called nerve cells. In most animals, nerve cells form a nervous system.
Receptor cells respond to sound, light, and external stimuli. Other nerve cells process information and determine how the animal responds.
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13. What Animals Do to Survive
Movement
Some animals stay at a single spot, but most can move. Most animals have muscles or musclelike tissues.
Muscle contraction enables motile animals to move around by working in combination with a support structure called a skeleton.
Muscles also help even sedentary animals feed and pump water and fluids through their bodies.
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14. What Animals Do to Survive
Reproduction
Most animals reproduce sexually. This helps to create and maintain genetic diversity in populations and improve species’ abilities to evolve when the environment changes.
Many invertebrates can also reproduce asexually. This produces offspring that are genetically identical to the parent. It allows animals to increase their numbers rapidly.
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15. Trends in Animal Evolution
Complex animals tend to have:
high levels of cell specialization and internal body organization
bilateral body symmetry
a front end or head with sense organs
a body cavity
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16. Trends in Animal Evolution
Cell Specialization and Levels of Organization
In multicellular organisms, each cell type has a structure and chemical composition that enable it to perform a specialized function.
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17. Trends in Animal Evolution
Groups of specialized cells form tissues.
Tissues join together to form organs and organ systems—all of which work together to carry out a variety of complex functions.
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18. Trends in Animal Evolution
Early Development
Animals that reproduce sexually begin life as a zygote, or fertilized egg.
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19. Trends in Animal Evolution
The zygote undergoes a series of divisions to form a blastula, a hollow ball of cells.
During the early development of animal embryos, cells divide to produce a hollow ball of cells called a blastula. An opening called a blastopore forms in this ball. In protostomes, the blastopore develops into the mouth. In deuterostomes, the blastopore forms an anus.
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20. Trends in Animal Evolution
The blastula folds in on itself, forming a single opening called a blastopore.
The blastopore leads into a central tube that runs the length of the developing embryo. This tube becomes the digestive tract and is formed in one of two ways.
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21. Trends in Animal Evolution
Ectoderm
A protostome is an animal whose mouth is formed from the blastopore.
Most invertebrate animals are protostomes.
Mesoderm
Endoderm
Blastopore
Anus
During the early development of animal embryos, cells divide to produce a hollow ball of cells called a blastula. An opening called a blastopore forms in this ball. In protostomes, the blastopore develops into the mouth.
Blastopore becomes mouth
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22. Trends in Animal Evolution
Ectoderm
A deuterostome is an animal whose anus is formed from the blastopore.
The anus is the opening through which wastes leave the digestive tract.
Mesoderm
Endoderm
Blastopore
Mouth
During the early development of animal embryos, cells divide to produce a hollow ball of cells called a blastula. An opening called a blastopore forms in this ball. In deuterostomes, the blastopore forms an anus.
Blastopore becomes anus
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23. Trends in Animal Evolution
Echinoderms and vertebrates are both deuterostomes.
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24. Trends in Animal Evolution
This similarity in embryology may indicate that vertebrates have a closer evolutionary relationship to echinoderms than to other invertebrates.
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25. Trends in Animal Evolution
During early development, the cells of most animal embryos differentiate into three layers called germ layers.
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26. Trends in Animal Evolution
The cells of the endoderm, or innermost germ layer, develop into the linings of the digestive tract and much of the respiratory system.
Only the label “endoderm” should appear on this slide.
Endoderm
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27. Trends in Animal Evolution
The cells of the mesoderm, or middle layer, develop into muscles and much of the circulatory, reproductive, and excretory organ systems.
Mesoderm
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28. Trends in Animal Evolution
The ectoderm, or outermost layer, develops into the sense organs, nerves, and the outer layer of the skin.
Ectoderm
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29. Trends in Animal Evolution
Body Symmetry
Except for sponges, every animal exhibits some body symmetry in its structure.
Many simple animals, like the sea anemone, have body parts that repeat around the center of the body.
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30. Trends in Animal Evolution
Radial symmetry
These animals exhibit radial symmetry, in which any number of imaginary planes can be drawn through the center, each dividing the body into equal halves.
Animals with radial symmetry, such as the sea anemone, have body parts that extend from a central point.
Planes of symmetry
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31. Trends in Animal Evolution
In animals with bilateral symmetry, only one imaginary plane can divide the body into two equal halves—left and right.
Plane of symmetry
Animals with bilateral symmetry, such as the crayfish, have distinct anterior and posterior ends and right and left sides.
Bilateral symmetry
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32. Trends in Animal Evolution
Posterior end
The anterior is the front end.
The posterior is the back end.
Anterior end
Animals with bilateral symmetry, such as the crayfish, have distinct anterior and posterior ends and right and left sides.
Bilateral symmetry
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33. Trends in Animal Evolution
The dorsal is the upper side.
The ventral is the lower side.
Dorsal side
Ventral side
Bilateral symmetry
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34. Trends in Animal Evolution
Bilateral symmetry allows for segmentation, in which the body is constructed of many repeated and similar parts, or segments.
The combination of bilateral symmetry and segmentation is found in two successful animal groups—arthropods and vertebrates.
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35. Trends in Animal Evolution
Cephalization
Animals with bilateral symmetry exhibit cephalization, which is the concentration of sense organs and nerve cells at the front end of the body.
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36. Trends in Animal Evolution
Animals with bilateral symmetry usually move with the anterior end forward, so this end comes in contact with new parts of the environment first.
As sense organs have evolved, they have tended to gather at the anterior end, as have nerve cells that process information and “decide” what the animal should do.
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37. Trends in Animal Evolution
Body Cavity Formation
Most animals have a body cavity, a fluid-filled space between the digestive tract and body wall.
A body cavity provides a space in which internal organs can be suspended so that they are not pressed on by muscles or twisted out of shape by body movements.
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