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Chapter 32 An Introduction to Animal Diversity PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What is an animal? • Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers. Several characteristics of animals sufficiently define the group: – Animals are heterotrophs that ingest their food – Animals are multicellular eukaryotes – The cell wall of animals LACKS a cell wall – Animal bodies are held together by structural proteins such as collagen – Nervous tissue and muscle tissue are unique to animals – Most animals reproduce sexually with the diploid stage usually dominating the life cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cleavage & Gastrulation in Animals • After a sperm fertilizes an egg the zygote undergoes cleavage, leading to the formation of a blastula – Cleavage is the process of cytokinesis in animal cells, characterized by pinching of the plasma membrane – and the succession of rapid cell divisions without growth during early embryonic development – CONVERTS ZYGOTE INTO A BALL OF CELLS – A blastula is a hollow ball of cells marking the end stage of cleavage during early embryonic development • 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). Hox Genes • All animals, and only animals have Hox genes that regulate the development of body form – Hox genes are special regulatory genes that control the transformation of a zygote to an animal of specific form • Hox genes are responsible for the development of “body parts” in animals – they specify the position of the body part on the developing embryo. • Mutations in hox genes result in the conversion of one body part to another. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Common Ancestor of Living Animals – The common ancestor of living animals was probably itself a colonial, flagellated protist 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 Figure 32.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Infolding Gastrula-like “protoanimal” Paleozoic Era (542–251 Million Years Ago) • The Cambrian explosion marks the earliest fossil appearance of many major groups of living animals Figure 32.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mesozoic Era (251–65.5 Million Years Ago) • During the Mesozoic era – Dinosaurs were the dominant terrestrial vertebrates – Coral reefs emerged, becoming important marine ecological niches for other organisms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cenozoic Era (65.5 Million Years Ago to the Present) • The beginning of this era – Followed mass extinctions of both terrestrial and marine animals • Modern mammal orders and insects – Diversified during the Cenozoic Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animal Body Plans • 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 – The set of morphological and developmental traits that define a grade are generally integrated into a functional whole referred to as a body plan Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body Symmetry in Animals • Animals can be categorized – According to the symmetry of their bodies, or lack of it – Radial v/s Bilateral Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Radial Symmetry • Some animals have radial symmetry – Like in a flower pot – these organisms are typically sessile in their environment (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 Bilateral Symmetry • 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 Bilateral Animals • Bilaterally symmetrical animals have – A dorsal (top) side and a ventral (bottom) side – A right and left side – Anterior (head) and posterior (tail) ends • Bilateral Symmetry facilitates cephalization, the development of a head – an evolutionary trend toward the concentration of sensory equipment on the anterior end (toward the head) – Bilateral organisms are typically motile in their environment 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 Germ Layer Formation during Gastrulation • Animal embryos form germ layers (embryonic tissues), including ectoderm, endoderm, and mesoderm – Ectoderm covers the surface of the embryo and gives rise to the outer covering of the animal – Endoderm is the innermost germ layer which lines the digestive tract and organs – Mesoderm lies between the endoderm and the ectoderm – it forms muscles and most other organs between the digestive tube and outer covering of the animal • Diploblastic animals have two germ layers • Triploblastic animals have three germ layers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body Cavities • In triploblastic animals a body cavity may be present or absent – A body cavity is a “tube-within-a-tube” body plan consisting of a fluid-filled space separating the digestive tract from the outer body wall. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Coelomates • A true body cavity is called a coelom and is derived from and completely lined with mesoderm – Annelids, Mollusks, Arthropods, Echinoderms, and Chordates 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) Pseudocoelomates • A pseudocoelom is a body cavity derived from the blastocoel, rather than from mesoderm – this body cavity is NOT completely lined with mesoderm – Nematodes & Rotifers Body covering (from ectoderm) Pseudocoelom (b) Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm. Digestive tract (from ectoderm) Figure 32.8b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Muscle layer (from mesoderm) Acoelomates • Organisms without body cavities are considered acoelomates – this is a “solid” body plan – Platyhelminthes (flatworms) 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) Feeding Systems in Coelomates and Acoelomates • Acoelomates, such as flatworms, have a gastrovascular cavity with only one opening – which serves as a dual role of mouth and anus. – This means that they lack a digestive tract altogether and absorb nutrients across their body surface. There is no specialization of compartments in this system. – Digestion is extracellular – meaning that the breakdown of food is outside the cells. • Coelomates, such as annelids, have a complete digestive tract that includes specialization along the tract. – This means that the digestive tube extends between two openings, the mouth and an anus. – Digestion is extracellular – meaning that the breakdown of food is outside the cells. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Embryonic Develop: Overview • Embryonic development consists of three stages: cleavage, gastrulation, and organogenisis. • Cleavage: rapid mitotic division of zygote occurring immediately after fertilization • Two Patterns: protostomes (spiral and determinate) and deuterostomes (radial and indeterminate) • In both groups, cleavage produces a fluidfilled ball of cells called a blastula. Cells of blastula are called blastomeres, and the fluid filled center is called the blastocoel. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Embryonic Develop: Overview • Gastrulation is a process that involves rearrangement of the blastula and begins with the formation of the blastopore (an opening into the blastula). – Blastopore becomes mouth in protostomes and anus in deuterostomes – Some cells on the surface of the embryo may migrate into the blastopore to form a new cavity called the archenteron or “primitive gut” – As a result of this cell movement, a threelayered embryo called a gastrula is formed Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Embryonic Develop: Overview • In most animals, the gastrula consists of three differentiated layers called the embryonic germ layers, each of which develops into all parts of the adult animal: – Endoderm – forms viscera including lungs, liver, and digestive organs – Ectoderm – becomes skin and nervous system – Mesoderm – gives rise to muscles, blood, and bones Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Embryonic Develop: Overview • Organogenesis is the process by which cells continue to differentiate, producing organs from the three embryonic germ layers – Once all organ systems have been developed, the embryo simply increases in size – http://bcs.whfreeman.com/thelifewire/content/chp20/2002001. html Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Order of Operations • As far as the AP Biology exam is concerned, the order of the stages and the various events is extremely important: • Zygote→Cleavage →Blastula →Gastrula →Organogenesis • You should know the order of the events and a description of each phase! Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Classifying Animals • Most animal phyla belong to the clade Bilateria • Vertebrates and some other phyla belong to the clade Deuterostomia • The morphology-based tree divides the bilaterians into two clades: deuterostomes and protostomes • In contrast, several recent molecular studies generally assign two sister taxa to the protostomes rather than one: the ecdysozoans and the lophotrochozoans Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecdysozoans • Ecdysozoans share a common characteristic – They shed their exoskeletons through a process called ecdysis Figure 32.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lophotrochozoans • Lophotrochozoans share a common characteristic called the lophophore, a feeding structure • Other phyla go through a distinct larval stage called a trochophore larva Apical tuft of cilia Mouth Figure 32.13a, b (a) An ectoproct, a lophophorate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anus (b) Structure of trochophore larva Morphological Phylogenetic Tree “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 Molecular Phylogenetic Tree 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