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.
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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