Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

29–1 Invertebrate Evolution Photo Credit: ©Brandon Cole/Visuals Unlimited Copyright Pearson Prentice Hall

Origin of Invertebrates Invertebrate fossils, dating between 575 and 543 million years ago, were discovered in the Ediacara Hills of Australia and in Chengjiang, China. The Ediacaran fossils include some of the earliest and most primitive animals known. Copyright Pearson Prentice Hall

Origin of Invertebrates 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 Copyright Pearson Prentice Hall

Origin of Invertebrates Some of these animals may have had photosynthetic algae living within their bodies. Some may have been related to soft-bodied invertebrates. They were probably simple and had little internal specialization. Copyright Pearson Prentice Hall

Origin of Invertebrates Beginnings of Invertebrate Diversity By the Cambrian Period, 544 million years ago, some animals had evolved shells, skeletons, and other hard body parts. One of the best-known sites of Cambrian fossils is the Burgess Shale of Canada. Copyright Pearson Prentice Hall

Origin of Invertebrates By the Cambrian period, animals had acquired specialized cells, tissues, and organs. During that time, the ancestors of most modern animal phyla first appeared in the fossil record. Copyright Pearson Prentice Hall

Origin of Invertebrates The animals of the Burgess Shale had many of the characteristics of modern day invertebrates including: body symmetry segmentation a skeleton a front and a back end appendages adapted for many functions Copyright Pearson Prentice Hall

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 Copyright Pearson Prentice Hall

Invertebrate Phylogeny Invertebrate Evolutionary Relationships This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals. Copyright Pearson Prentice Hall

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 Copyright Pearson Prentice Hall

Invertebrate Phylogeny This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals. Copyright Pearson Prentice Hall

Invertebrate Phylogeny This diagram illustrates one recent theory about the phylogenetic relationships among groups of living animals. Copyright Pearson Prentice Hall

Invertebrate Phylogeny What are the major trends in invertebrate evolution? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends Evolutionary Trends The appearance of each phylum in the fossil record represents the evolution of a successful and unique body plan. Features of this body plan typically change over time, leading to the formation of many new traits. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends Specialized Cells, Tissues, and Organs As larger and more complex animals evolved, specialized cells joined together to form tissues, organs, and organ systems that work together to carry out complex functions. Flatworms have simple organs for digestion, excretion, response, and reproduction. More complex animals, such as mollusks and arthropods, have organ systems. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends Body Symmetry All invertebrates, except sponges, exhibit some type of body symmetry. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends Cnidarians and echinoderms exhibit radial symmetry where parts extend from the center of the body. Radial symmetry Planes of symmetry Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends Worms, mollusks, and arthropods exhibit bilateral symmetry, or have mirror-image left and right sides. Bilateral symmetry Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evolutionary Trends Embryological Development   In most invertebrates, the zygote divides to form a blastula—a hollow ball of cells. In protostomes, the blastopore, or the opening of the blastula, develops into a mouth. In deuterostomes, the blastopore forms an anus. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 29–1 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 29–1 According to the most recent studies of animal fossils, which of the following is correct? Annelids with a true coelom appeared before cnidarians with two germ layers. Radial symmetry appears in cnidarians and adult echinoderms. Protostome development appears after deuterostome development. Bilateral symmetry appears before tissues. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 29–1 Acoelomates lack tissues. a coelom. radial symmetry. specialized cells. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 29–1 Worms, mollusks, and arthropods exhibit bilateral symmetry. radial symmetry. no internal specialization. similar larval forms. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 29–1 In most invertebrates, the zygote divides repeatedly to form a coelom. digestive tract. blastula. mesoderm. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 29–1 The animal group that has no germ layers, body symmetry, cephalization, or coelom is the flatworms. annelids. sponges. cnidarians. Copyright Pearson Prentice Hall

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