Chapter 18 Lecture

Chapter 18 Lecture - 1 Chapter 18 The Evolution of...

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1 Chapter 18 Chapter 18 The Evolution of Invertebrate Diversity 2 3 ANIMAL EVOLUTION AND DIVERSITY 4 18.1 What is an animal? ± Animals are – eukaryotic, – multicellular heterotrophs, and – have cells that lack cell walls. ± Animals also use ingestion , the eating of food. ± Fungi absorb nutrients after digesting food outside their body. 5 18.1 What is an animal? ± Most adult animals are diploid and reproduce sexually. – The eggs and sperm – are produced by meiosis, – are the only haploid cells, and – fuse during fertilization to form a zygote. – The zygote divides by mitosis to form a hollow ball of cells called a blastula . 6 18.1 What is an animal? ± One side of the blastula folds in and cells become rearranged to form a gastrula that establishes three embryonic layers. Endoderm forms a lining of the future digestive tract. Ectoderm forms an outer layer that will give rise to the skin and nervous system. Mesoderm forms a middle layer that will give rise to muscles and most internal organs. 7 18.1 What is an animal? ± After the gastrula stage, many animals develop directly into adults. ± Other animals, such as the sea star, develop into one or more larval stages. –A larva is an immature individual that looks different from the adult animal. – A larva undergoes a major change in body form, called metamorphosis , and becomes a reproductively mature adult. ± Clusters of master control homeotic genes control transformation of the zygote into an adult animal. 8 9 18.2 Animal diversification began more than half a billion years ago ± The oldest generally accepted animal fossils that have been found are 575–550 million years old. ± Animal diversification appears to have accelerated rapidly from 535 to 525 million years ago, during the Cambrian period, known as the Cambrian explosion. ± The most celebrated source of Cambrian fossils is the Burgess Shale containing numerous perfectly preserved animal fossils. 10 11 12 18.2 Animal diversification began more than half a billion years ago
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± The Cambrian explosion may have been caused by – increasingly complex predator-prey relationships or – an increase in atmospheric oxygen. ± Much of the diversity in body form among the animal phyla is associated with variations in where and when homeotic genes are expressed within developing embryos. ± Of the 35 or so animal phyla, all but one are invertebrates, named because they lack vertebra. 13 18.3 Animals can be characterized by basic features of their “body plan” ± Animal body plans vary in –symme t ry , – presence of true tissues, – number of embryonic layers,
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This note was uploaded on 11/06/2011 for the course BIOL 1402 taught by Professor Atanasov during the Fall '08 term at Texas Tech.

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Chapter 18 Lecture - 1 Chapter 18 The Evolution of...

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