Chapter 32

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Chapter 32. An Introduction to Animal Diversity. Overview: Welcome to Your Kingdom. The animal kingdom extends far beyond humans and other animals we may encounter 1.3 million living species of animals have been identified.
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Chapter 32An Introduction to Animal DiversityOverview: Welcome to Your Kingdom
  • The animal kingdom extends far beyond humans and other animals we may encounter
  • 1.3 million living species of animals have been identified
  • Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
  • There are exceptions to nearly every criterion for distinguishing animals from other life-forms
  • Several characteristics, taken together, sufficiently define the group
  • Nutritional Mode
  • Animals are heterotrophs that ingest their food
  • Cell Structure and Specialization
  • Animals are multicellular eukaryotes
  • Their cells lack cell walls
  • Their bodies are held together by structural proteins such as collagen
  • Nervous tissue and muscle tissue are unique to animals
  • 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 rapid cell division called cleavage
  • Cleavage leads to formation of a blastula
  • The blastula undergoes gastrulation, forming a gastrulawith different layers of embryonic tissues
  • Fig. 32-2-3Embryonic Development in AnimalsBlastocoelEndodermCleavageCleavageBlastulaEctodermArchenteronEight-cell stageMORULAZygoteGastrulationGastrulaBlastocoelBlastoporeCross sectionof blastulaMany animals have at least one larval stage
  • A larvais sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis
  • All animals, and only animals, have Hox genes that regulate the development of body form
  • Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology
  • Concept 32.2: The history of animals spans more than half a billion years
  • The animal kingdom includes a great diversity of living species and an even greater diversity of extinct ones
  • The common ancestor of living animals may have lived between 675 and 875 million years ago
  • This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals
  • Fig. 32-3IndividualchoanoflagellateChoanoflagellatesOTHEREUKARYOTESSpongesAnimalsCollar cell(choanocyte)Other animalsNeoproterozoic Era (1 Billion–524 Million Years Ago)
  • Early members of the animal fossil record include the Ediacaran biota,which dates from 565 to 550 million years ago
  • radial symetrymany body segmentsPaleozoic Era (542–251 Million Years Ago)
  • The Cambrian explosion(535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals
  • There are several hypotheses regarding the cause of the Cambrian explosion
  • New predator-prey relationships
  • A rise in atmospheric oxygen
  • Hox gene evolution
  • Animal diversity continued to increase
  • mass extinctions
  • vertebrates appeared 460 mya (fishes)
  • made the transition to land circa 360 mya
  • Mesozoic Era (251–65.5 Million Years Ago)
  • Coral reefs emerged, becoming important marine ecological niches for other organisms
  • During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates
  • The first mammals emerged
  • Cenozoic Era (65.5 Million Years Ago to the Present)
  • The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals
  • These extinctions included the large, nonflying dinosaurs and the marine reptiles
  • Modern mammal orders and insects diversified during the Cenozoic
  • Concept 32.3: Animals can be characterized by “body plans”
  • Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits
  • A grade is a group whose members share key biological features
  • A grade is not necessarily a clade, or group that share a same ancestral species
  • Symmetry
  • Animals can be categorized according to the symmetry of their bodies, or lack of it
  • Some animals have radial symmetry
  • Two-sided symmetry is called bilateral symmetry
  • radial symmetrybilateral symmetryBilatera Symmetry
  • A dorsal(top) side and a ventral(bottom) side
  • A right and left side
  • Anterior(head) and posterior(tail) ends
  • Cephalization, the development of a head
  • 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
  • During development, three germ layers give rise to the tissues and organs of the animal embryo
  • Ectodermis the germ layer covering the embryo’s surface
  • Endodermis the innermost germ layer and lines the developing digestive tube, called the archenteron
  • Diploblastic animals have ectoderm and endoderm
  • Triploblastic animals also have an intervening mesodermlayer; these include all bilaterians
  • Body Cavities
  • Most triploblastic animals possess a body cavity
  • A true body cavity is called a coelomand is derived from mesoderm
  • Coelomatesare animals that possess a true coelom
  • coelombody covering (from ectoderm)tissue layer lining coelom and suspendinginternal organs (from mesoderm)digestive tract (from endoderm)A pseudocoelom is a body cavity derived from the mesoderm and endoderm
  • Triploblastic animals that possess a pseudocoelom are called pseudocoelomates
  • body covering (from ectoderm)coelomMuscle layer (from mesoderm)digestive tract (from endoderm)Triploblastic animals that lack a body cavity are called acoelomatesbody covering (from ectoderm)tissue filled region (from mesoderm)wall of digestive cavity (from endoderm)Protostome and Deuterostome Development
  • Based on early development, many animals can be categorized as having protostome developmentor deuterostome development
  • Cleavage
  • In protostome development, cleavage is spiraland determinate
  • In deuterostome development, cleavage is radialand indeterminate
  • With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo
  • Indeterminate cleavage makes possible identical twins, and embryonic stem cells
  • Eight-cell stagemollusca, annelids, arthropodsEight-cell stageechinoderms, chordatesSpiral and determinateRadial and indeterminateCoelom Formation
  • In protostome development, the splitting of solid masses of mesoderm forms the coelom
  • In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom
  • Eight-cell stagemollusca, annelids, arthropodsEight-cell stageechinoderms, chordatesmesodermArchenteroncoelomectodermmesodermcoelomblastoporeFig. 32-9cProtostome development(examples: molluscs,annelids)Deuterostome development(examples: echinoderms,chordates)(c) Fate of the blastoporeAnusMouthKeyEctodermDigestive tubeMesodermEndodermAnusMouthMouth develops from blastopore.Anus develops from blastopore.Concept 32.4: New views of animal phylogeny are emerging from molecular data
  • Zoologists recognize about three dozen animal phyla
  • Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well
  • Fig. 32-10“Porifera”CnidariaANCESTRALCOLONIALFLAGELLATEMetazoaCtenophoraEumetazoaEctoproctaBrachiopodaDeuterostomiaOne hypothesis is based on themorphological and developmentalcomparisonEchinodermataChordataBilateriaPlatyhelminthesRotiferaProtostomiaMolluscaAnnelidaArthropodaNematodaFig. 32-11Silicea“Porifera”CalcareaANCESTRALCOLONIALFLAGELLATEMetazoaCtenophoraCnidariaEumetazoaAcoelaAnother hyopothesis views animal phelogeny based on molecular dataEchinodermataDeuterostomiaChordataBilateriaPlatyhelminthesRotiferaEctoproctaLophotrochozoaBrachiopodaMolluscaAnnelidaNematodaEcdysozoaArthropodaPoints of Agreement
  • All animals share a common ancestor
  • Sponges are basal animals
  • Eumetazoa is a clade of animals (eumetazoans) with true tissues
  • Most animal phyla belong to the clade Bilateria, and are called bilaterians
  • Chordates and some other phyla belong to the clade Deuterostomia
  • Progress in Resolving Bilaterian Relationships
  • The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes
  • In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa
  • Ecdysozoansshed their exoskeletons through a process called ecdysis
  • nematodes andarthropodesSome lophotrochozoanshave a feeding structure called a lophophore
  • Other phyla go through a distinct developmental stage called the trochophore larva
  • Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history
  • apical tuft of cilialophos= crestpherein= to carryplathyhelminthesrotifersmolluscsannelidsTrochophorelarvamouthanusThe End
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