A cladogram of Nonchordate Invertebrates.

FIGURE 26–3 Cladogram of Nonchordate Invertebrates This diagram shows current hypotheses of evolutionary relationships among major groups of animals. During the course of evolution that produced these different groups, important traits evolved. These are shown by the red circles (nodes). Note that the invertebrate chordates, which you will learn about in the next lesson, are not shown. Also, note that nonchordate invertebrates do not form a clade.

d

Nonchordate Invertebrates

What does the cladogram of nonchordate invertebrates illustrate?

The groups of living invertebrates are shown in Figure 26–3. The cladogram of nonchordate invertebrates presents current hypotheses about evolutionary relationships among major groups of modern invertebrates. It also indicates the sequence in which some important features evolved. These features include body symmetry, cephalization, segmentation, and formation of a coelom. Many of these features evolved in Cambrian animals.

INVERTEBRATEPHYLUMDESCRIPTION

A photograph of sponges on sea bed and a drawing of sponges.

Sponges are members of the phylum Porifera (por IHF er uh), which means “pore bearers” in Latin, reflecting the fact that they have tiny openings, or pores, all over their bodies.

Sponges are classified as animals because they are multicellular, heterotrophic, lack cell walls, and contain a few specialized cells. Sponges are the most ancient members of the kingdom Animalia and are among the simplest organisms to be placed in the clade Metazoa, with all other multicellular animals.

DOL•31

A photograph of cnidarian on sea bed and a drawing of cnidarian.

Jellyfishes, sea fans, sea anemones, hydras, and corals are all members of the phylum Cnidaria (ny DAYR ee uh).

Cnidarians are aquatic, soft-bodied, carnivorous, radially symmetrical animals with stinging tentacles arranged in circles around their mouths. Some, such as corals, have skeletons. They are the simplest animals to have body symmetry and specialized tissues. Some cnidarians live as independent individuals. Others live in colonies composed of many individuals. DOL•32–DOL•33

End ofPage 754

Table of Contents

Miller & Levine Biology
About the Authors
Changing the World of Biology Education
Contents
Diversity of Life: A Visual Guide DOL•1–DOL•64
Labs and Activities
Features
UNIT 1 The Nature of Life
1 The Science of Biology
2 The Chemistry of Life
Unit Project
UNIT 2 Ecology
3 The Biosphere
4 Ecosystems and Communities
5 Populations
6 Humans in the Biosphere
Unit Project
UNIT 3 Cells
7 Cell Structure and Function
8 Photosynthesis
9 Cellular Respiration and Fermentation
10 Cell Growth and Division
Unit Project
UNIT 4 Genetics
11 Introduction to Genetics
12 DNA
13 RNA and Protein Synthesis
14 Human Heredity
15 Genetic Engineering
Unit Project
UNIT 5 Evolution
16 Darwin's Theory of Evolution
17 Evolution of Populations
18 Classification
19 History of Life
Unit Project
UNIT 6 From Microorganisms to Plants
20 Viruses and Prokaryotes
21 Protists and Fungi
22 Introduction to Plants
23 Plant Structure and Function
24 Plant Reproduction and Response
Unit Project
UNIT 7 Animals
25 Introduction to Animals
26 Animal Evolution and Diversity
27 Animal Systems I
28 Animal Systems II
29 Animal Behavior
Unit Project
UNIT 8 The Human Body
30 Digestive and Excretory Systems
31 Nervous System
32 Skeletal, Muscular, and Integumentary Systems
33 Circulatory and Respiratory Systems
34 Endocrine and Reproductive Systems
35 Immune System and Disease
Unit Project
A Visual Guide to The Diversity of Life
HOW TO USE THIS GUIDE
THE TREE OF LIFE
Bacteria
Protists
Fungi
Plants
Animals
Appendices
Appendix A Science Skills
Appendix B Lab Skills
Appendix C Technology & Design
Appendix D Math Skills
Appendix E Periodic Table
Glossary
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q, R
S
T
U
V
W
X, Y, Z
Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Credits
Go to previous page Go to next page