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Chapter 32 An Introduction to Animal Diversity “Abridged” version! PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Welcome to Your Kingdom • Animal are multicellular • Heterotrophic; must ingest their food • Eukaryotes, with cells lacking cell walls • Tissues that develop from embryonic layers – their bodies are held together by structural proteins such as collagen – Nervous tissue and muscle tissue are unique to animals Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The common ancestor of living animals – May have lived 1.2 billion–800 million years ago – May have resembled modern choanoflagellates, protists that are the closest living relatives of animals Single cell Stalk (a) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) • Several characteristics of animals sufficiently define their grouping and levels of complexity – Body plan • Symmetry • Tissues (types, layers) • Body cavities (acoelomate, pseudocoelomate, eucoelomate) – Reproduction and development Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 32.3: Animals can be characterized by “body plans” • One way in which zoologists categorize the diversity of animals – Is according to general features of morphology and development • A group of animal species – That share the same level of organizational complexity is known as a grade Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissues • Animal body plans – Also vary according to the organization of the animal’s tissues • Tissues – Are collections of specialized cells isolated from other tissues by membranous layers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Animal embryos – Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm • Diploblastic animals – Have two germ layers • Triploblastic animals – Have three germ layers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some animals have radial symmetry – Like in a flower pot (a) Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images. Figure 32.7a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some animals exhibit bilateral symmetry – Or two-sided symmetry (b) Bilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves. Figure 32.7b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Bilaterally symmetrical animals have – A dorsal (top) side and a ventral (bottom) side – A right and left side (lateral) – Anterior (head) and posterior (tail) ends – Cephalization, the development of a head with senses concentrated in one area, is considered an evolutionary step forward Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body Cavities • In triploblastic animals – A body cavity may be present or absent Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A true body cavity – Is called a coelom and is derived from mesoderm Coelom (a) Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm. Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Figure 32.8a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body covering (from ectoderm) • A pseudocoelom – Is a body cavity derived from the blastocoel, rather than from mesoderm Body covering (from ectoderm) (b) Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm. Pseudocoelom Digestive tract (from ectoderm) Figure 32.8b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Muscle layer (from mesoderm) • Organisms without body cavities – Are considered acoelomates Body covering (from ectoderm) (c) Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall. Digestive tract (from endoderm) Figure 32.8c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissuefilled region (from mesoderm) Reproduction and Development • Most animals reproduce sexually – With the diploid stage usually dominating the life cycle • After a sperm fertilizes an egg – The zygote undergoes cleavage, leading to the formation of a blastula • The blastula undergoes gastrulation – Resulting in the formation of embryonic tissue layers and a gastrula Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Early embryonic development in animals 1 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 2 Only one cleavage stage–the eight-cell embryo–is shown here. 3 In most animals, cleavage results in the formation of a multicellular stage called a blastula. The blastula of many animals is a hollow ball of cells. Blastocoel Cleavage Cleavage 6 The endoderm of the archenteron develops into the tissue lining the animal’s digestive tract. Zygote Eight-cell stage Blastula Cross section of blastula Blastocoel Endoderm 5 The blind pouch formed by gastrulation, called the archenteron, opens to the outside via the blastopore. Ectoderm Gastrula Gastrulation Blastopore Figure 32.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer). Digestive cavity Somatic cells Reproductive cells Colonial protist, an aggregate of identical cells Hollow sphere of unspecialized cells (shown in cross section) Beginning of cell specialization Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Infolding Gastrula-like “protoanimal” Protostome and Deuterostome Development • Based on certain features seen in early development – Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cleavage • In protostome development – Cleavage is spiral and determinate • In deuterostome development – Cleavage is radial and indeterminate Protostome development (examples: molluscs, annelids, arthropods) Eight-cell stage Spiral and determinate Deuterostome development (examples: echinoderms, chordates) Eight-cell stage Radial and indeterminate Figure 32.9a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) Cleavage. In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage. Coelom Formation • In protostome development – The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development • In deuterostome development – Formation of the body cavity is described as enterocoelous development Coelom Archenteron Coelom Mesoderm Blastopore Mesoderm Blastopore Enterocoelous: Schizocoelous: solid folds of archenteron masses of mesoderm form coelom split and form coelom Figure 32.9b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development). Fate of the Blastopore • In protostome development – The blastopore becomes the mouth • In deuterostome development – The blastopore becomes the anus Mouth Anus Digestive tube Mouth Figure 32.9c Mouth develops from blastopore Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anus Anus develops from blastopore • Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree • Zoologists currently recognize about 35 animal phyla • The current debate in animal systematics – Has led to the development of two phylogenetic hypotheses, but others exist as well Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Arthropoda Nematoda Rotifera Annelida Mollusca Nemertea Platyhelminthes Ectoprocta Phoronida Brachiopoda Chordata Echinodermata Cnidaria Ctenophora Silicarea Calcarea • One hypothesis of animal phylogeny based mainly on molecular data “Radiata” “Porifera” Deuterostomia Lophotrochozoa Bilateria Eumetazoa Metazoa Figure 32.11 Ancestral colonial flagellate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecdysozoa “Radiata” Deuterostomia Metazoa Figure 32.10 Ancestral colonial flagellate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nematoda Nemertea Rotifera Arthropoda Annelida Protostomia Bilateria Eumetazoa Mollusca Platyhelminthes Chordata Echinodermata Brachiopoda Ectoprocta Phoronida Ctenophora Cnidaria Porifera • One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons