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Fig. 26-3 Species: Panthera pardus Genus: Panthera Family: Felidae Order: Carnivora Class: Mammalia Phylum: Chordata Kingdom: Animalia Bacteria Domain: Eukarya Archaea Fig. 26-4 Order Family Genus Species Taxidea Taxidea taxus Lutra Mustelidae Panthera Felidae Carnivora Panthera pardus Lutra lutra Canis Canidae Canis latrans Canis lupus • Linnaean classification and phylogeny can differ from each other • Systematists have proposed the PhyloCode, which recognizes only groups that include a common ancestor and all its descendents • A phylogenetic tree represents a hypothesis about evolutionary relationships • Each branch point represents the divergence of two species • Sister taxa are groups that share an immediate common ancestor • A rooted tree includes a branch to represent the last common ancestor of all taxa in the tree • A polytomy is a branch from which more than two groups emerge Fig. 26-5 Branch point (node) Taxon A Taxon B Taxon C ANCESTRAL LINEAGE Taxon D Taxon E Taxon F Common ancestor of taxa A–F Polytomy Sister taxa Applying Phylogenies • Phylogeny provides important information about similar characteristics in closely related species • A phylogeny was used to identify the species of whale from which “whale meat” originated Fig. 26-6 RESULTS Minke (Antarctica) Minke (Australia) Unknown #1a, 2, 3, 4, 5, 6, 7, 8 Minke (North Atlantic) Unknown #9 Humpback (North Atlantic) Humpback (North Pacific) Unknown #1b Gray Blue (North Atlantic) Blue (North Pacific) Unknown #10, 11, 12 Unknown #13 Fin (Mediterranean) Fin (Iceland) • Phylogenies of anthrax bacteria helped researchers identify the source of a particular strain of anthrax Fig. 26-UN1 (a) A B D B D C C C B D A A (b) (c) Sorting Homology from Analogy • When constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy • Homology is similarity due to shared ancestry • Analogy is similarity due to convergent evolution Fig. 26-7 Evaluating Molecular Homologies • Systematists use computer programs and mathematical tools when analyzing comparable DNA segments from different organisms Fig. 26-8 1 Deletion 2 Insertion 3 4 • It is also important to distinguish homology from analogy in molecular similarities • Mathematical tools help to identify molecular homoplasies, or coincidences • Molecular systematics uses DNA and other molecular data to determine evolutionary relationships Fig. 26-9 Amino acids specified by each codon sequence on mRNA Ala: Alanine Cys: Cysteine Asp: Aspartic acid Glu: Glutamic acid Phe: Phenylalanine Gly: Glycine His: Histidine Ile: Isoleucine Lys: Lysine Leu: Leucine Met: Methionine Asn: Asparagine Pro: Proline Gln: Glutamine Arg: Arginine Ser: Serine Thr: Threonine Val: Valine Trp: Tryptophane Tyr: Tyrosisne A = adenine G = guanine C = cytosine T = thymine U = uracil Mus musculus lactate dehydrogenase C (Ldhc), mRNA • • • • • • • • • • • • • • • • • • • • • • 1 atcctggttt cttacctgtg ctgcggagtc agcagtaagg ctcaacatgt ccaccgtcaa 61 ggagcagctg attcagaacc tagttccgga agataaactt tcccggtgta agattactgt 121 ggtcggagtt ggaaatgtgg gcatggcgtg tgctattagt attttactga agggtttggc 181 tgatgaactt gcccttgttg acgctgatac gaacaaactg aggggagagg cactggatct 241 tctgcacggc agtcttttcc ttagcactcc aaaaatcgtc tttggaaaag attacaatgt 301 atctgccaac tccaaactgg ttattatcac agctggtgca agaatggtgt ctggagaaac 361 tcgccttgac ctgctccaac gtaatgtcgc tatcatgaaa gccattgttc cgggcattgt 421 ccaaaacagt ccggactgta aaataattat cgtcactaac ccagtggata ttttgacata 481 cgtggtttgg aagataagcg gcttccctgt aggccgtgtg atcggaagtg gctgtaacct 541 agactcagca cgttttcgtt acctgattgg ggagaagctg ggtgtcaacc ctacaagctg 601 ccacggctgg gttcttggag aacatgggga ctccagtgtg cccatatgga gtggtgtaaa 661 cgttgctggc gtaactctga agtcactgaa cccagcaata ggaactgact cagataagga 721 acactggaaa aatgttcaca agcaggtggt ggaaggcggc tatgaggtcc ttaacatgaa 781 gggctatacc tcttgggcta tcgggctgtc tgtgactgat ctggcgcgat ccatcttgaa 841 gaatcttaag agagtgcatc ctgttaccac gctggttaag ggcttccatg ggataaagga 901 agaggtcttc ctcagtatcc cttgtgtctt gggacaaagt ggtatcacag actttgtgaa 961 agtcaacatg accgctgagg aggagggtct cctcaagaag agtgcggaca cactctggaa 1021 tatgcagaag gatctgcagt tataaactcg ccaccttcga ccgtgtgaca gatgcctgat 1081 cacatcactg atcacggcag tcccactgaa agtgtttcca catcataaca aagttcaata 1141 aaattttgga aacctgttaa gatcaatctc aaggctagaa agattaatgc caaaggcatc 1201 tccctccccc tttttttgag acagggtctc actttatagc cttagctgac ctcaaacgga 1261 aatctgctag cctcccagtg tattaaaggc aaccaccacc aggcccagct Cladistics • Cladistics groups organisms by common descent • A clade is a group of species that includes an ancestral species and all its descendants • Clades can be nested in larger clades, but not all groupings of organisms qualify as clades • A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants Fig. 26-10 A A A B B C C C D D D E E F F F G G G B Group I (a) Monophyletic group (clade) Group II (b) Paraphyletic group E Group III (c) Polyphyletic group • A shared ancestral character is a character that originated in an ancestor of the taxon • A shared derived character is an evolutionary novelty unique to a particular clade • A character can be both ancestral and derived, depending on the context Inferring Phylogenies Using Derived Characters • When inferring evolutionary relationships, it is useful to know in which clade a shared derived character first appeared Fig. 26-11 TAXA Tuna Leopard Lancelet (outgroup) Vertebral column (backbone) 0 1 1 1 1 1 Hinged jaws 0 0 1 1 1 1 Lamprey Tuna Vertebral column Salamander Hinged jaws Four walking legs 0 0 0 1 1 1 Turtle Four walking legs Amniotic (shelled) egg 0 0 0 0 1 1 Hair 0 0 0 0 0 1 Amniotic egg (a) Character table Leopard Hair (b) Phylogenetic tree • An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied • Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared ancestral characteristics Phylogenetic Trees with Proportional Branch Lengths • In some trees, the length of a branch can reflect the number of genetic changes that have taken place in a particular DNA sequence in that lineage Fig. 26-12 Drosophila Lancelet Zebrafish Frog Chicken Human Mouse • In other trees, branch length can represent chronological time, and branching points can be determined from the fossil record Fig. 26-13 Drosophila Lancelet Zebrafish Frog Chicken Human Mouse PALEOZOIC 542 MESOZOIC 251 Millions of years ago CENOZOIC 65.5 Present • Maximum parsimony assumes that the tree that requires the fewest evolutionary events (appearances of shared derived characters) is the most likely • The principle of maximum likelihood states that, given certain rules about how DNA changes over time, a tree can be found that reflects the most likely sequence of evolutionary events Fig. 26-14 Human Mushroom Tulip 0 30% 40% 0 40% Human Mushroom 0 Tulip (a) Percentage differences between sequences 15% 5% 5% 15% 15% 10% 20% 25% Tree 1: More likely Tree 2: Less likely (b) Comparison of possible trees • Computer programs are used to search for trees that are parsimonious and likely Fig. 26-15-1 Species I Species III Species II Three phylogenetic hypotheses: I I III II III II III II I Fig. 26-15-2 Site 1 2 3 4 Species I C T A T Species II C T T C Species III A G A C Ancestral sequence A G T T 1/C I 1/C II I III III II 1/C II III 1/C I 1/C Fig. 26-15-3 Site 1 2 3 4 Species I C T A T Species II C T T C Species III A G A C Ancestral sequence A G T T 1/C I 1/C II I III III II 1/C II III I 1/C 3/A 2/T I 2/T 3/A 3/A 4/C II II 2/T 4/C III 2/T 4/C III 3/A 4/C I III II 4/C 1/C I 2/T 3/A Fig. 26-15-4 Site 1 2 3 4 Species I C T A T Species II C T T C Species III A G A C Ancestral sequence A G T T 1/C I 1/C II I III III II 1/C II III I 1/C 3/A 2/T I 2/T 3/A 3/A 4/C 3/A 4/C III II 2/T 4/C II III 6 events I III II 4/C 1/C I 2/T 3/A 2/T 4/C I I III II III II III II I 7 events 7 events Phylogenetic Trees as Hypotheses • The best hypotheses for phylogenetic trees fit the most data: morphological, molecular, and fossil • Phylogenetic bracketing allows us to predict features of an ancestor from features of its descendents Fig. 26-16 Lizards and snakes Crocodilians Common ancestor of crocodilians, dinosaurs, and birds Ornithischian dinosaurs Saurischian dinosaurs Birds • This has been applied to infer features of dinosaurs from their descendents: birds and crocodiles Animation: The Geologic Record Fig. 26-17 Front limb Hind limb Eggs (a) Fossil remains of Oviraptor and eggs (b) Artist’s reconstruction of the dinosaur’s posture Gene Duplications and Gene Families • Gene duplication increases the number of genes in the genome, providing more opportunities for evolutionary changes • Like homologous genes, duplicated genes can be traced to a common ancestor • Orthologous genes are found in a single copy in the genome and are homologous between species • They can diverge only after speciation occurs • Paralogous genes result from gene duplication, so are found in more than one copy in the genome • They can diverge within the clade that carries them and often evolve new functions Fig. 26-18 Ancestral gene Ancestral species Speciation with divergence of gene Species A Orthologous genes Species B (a) Orthologous genes Species A Gene duplication and divergence Paralogous genes Species A after many generations (b) Paralogous genes Molecular Clocks • A molecular clock uses constant rates of evolution in some genes to estimate the absolute time of evolutionary change • In orthologous genes, nucleotide substitutions are proportional to the time since they last shared a common ancestor • In paralogous genes, nucleotide substitutions are proportional to the time since the genes became duplicated • Molecular clocks are calibrated against branches whose dates are known from the fossil record Fig. 26-19 90 60 30 0 0 30 60 90 Divergence time (millions of years) 120 From Two Kingdoms to Three Domains • Early taxonomists classified all species as either plants or animals • Later, five kingdoms were recognized: Monera (prokaryotes), Protista, Plantae, Fungi, and Animalia • More recently, the three-domain system has been adopted: Bacteria, Archaea, and Eukarya • The three-domain system is supported by data from many sequenced genomes Animation: Classification Schemes Fig. 26-21 EUKARYA Dinoflagellates Forams Ciliates Diatoms Red algae Land plants Green algae Cellular slime molds Amoebas Euglena Trypanosomes Leishmania Animals Fungi Sulfolobus Green nonsulfur bacteria Thermophiles Halophiles (Mitochondrion) COMMON ANCESTOR OF ALL LIFE Methanobacterium ARCHAEA Spirochetes Chlamydia Green sulfur bacteria BACTERIA Cyanobacteria (Plastids, including chloroplasts) Fig. 26-UN2 Node Taxon A Taxon B Sister taxa Taxon C Taxon D Taxon E Most recent common ancestor Polytomy Taxon F Fig. 26-UN3 Monophyletic group A A A B B B C C C D D D E E E F F F G G G Paraphyletic group Polyphyletic group Fig. 26-UN4 Salamander Lizard Goat Human Fig. 26-UN5 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 gastrula with different layers of embryonic tissues Video: Sea Urchin Embryonic Development Fig. 32-2-3 Blastocoel Cleavage Endoderm Cleavage Blastula Ectoderm Zygote Eight-cell stage Gastrulation Blastocoel Cross section of blastula Gastrula Blastopore Archenteron • One important class of transcription factors is encoded by the so-called homeotic, or Hox, genes. Found in all animals, Hox genes act to "regionalize" the body along the embryo's anterior-toposterior (head-to-tail) axis. In a fruit fly, for example, Hox genes lay out the various main body segments—the head, thorax, and abdomen. Here we see a representation of a fruit fly embryo viewed from the side, with its anterior end to the left and with various Hox genes shown in different colors. Each Hox gene, such as the blue Ultrabithorax or Ubx gene, is expressed in different areas, or domains, along the anterior-to-posterior axis. The arced, colored bars give an idea of the full range, or domain, of each gene's expression. Synopsis of Drosophila development from egg to adult fly • • The upper diagrams show the fates of the different regions of the egg/early embryo and indicate (in white) the parts that fail to develop if the anterior, posterior, or terminal system is defective. The middle row shows schematically the appearance of a normal larva and of mutant larvae that are defective in a gene of the anterior system (for example, bicoid), of the posterior system (for example, nanos), or of the terminal system (for example, torso). The bottom row of drawings shows the appearances of larvae in which none or only one of the three gene systems is functional. The lettering beneath each larva specifies which systems are intact (A P T for a normal larva, -P T for a larva where the anterior system is defective but the posterior and terminal systems are intact, and so on). Inactivation of a particular gene system causes loss of the corresponding set of body structures; the body parts that form correspond to the gene systems that remain functional. Note that larvae with a defect in the anterior system can still form terminal structures at their anterior end, but these are of the type normally found at the rear end of the body rather than the front of the head. (Slightly modified from D. St. Johnston and C. NüssleinVolhard, Cell 68:201–219, 1992.) • • Edward B.Lewis at the California Institute of Technology in Pasadena was interested in questions concerning certain developmental changes in the Drosophila fly and how the genes causing them cooperate during body segmentation. The answers he got, laid the foundation of one of the most surprising discoveries in developmental biology - the same type of genes which controls the early embryonic development of Drosophila also controls the early embryogenesis of a lot of higher organisms, including man. This means that the genetic control mechanisms have been preserved roughly unchanged through 650 million years of evolution! A starting point for Lewis in his research on the genetic basis for so-called homeotic transformations during early embryonic development was his work with the now famous Drosophila-mutant with four wings instead of two. Homeotic genes control specialization of the segments. In the mutantcase inactivity of the first gene in a complex of homeotic genes (the bithorax complex) caused other homeotic genes to duplicate the segment with two wings. Lewis' pioneering work on the bithorax genes led to his discovery of the colinearity principle. According to this principle there is a co-linearity in time and space between the order of the genes in the bithorax complex and their effect regions in the segments. This discovery has had a very large influence on later developmental research. • a | The panel on the left shows a stage 13 Drosophila melanogaster embryo that has been coloured in the schematic to indicate the approximate domains of transcription expression for all Hox genes except proboscipedia (pb)85. The segments are labelled (Md, mandibular; Mx, maxillary; Lb, labial; T1–T3, thoracic segments; A1–A9, abdominal segments). The panel on the right shows a mouse (Mus musculus) embryo, at embryonic day 12.5, with approximate Hox expression domains depicted on the head–tail axis of the embryo. The positions of hindbrain RHOMBOMERES R1, R4 and R7 are labelled. In both diagrams the colours that denote the expression patterns of the Hox transcripts are colour-coded to the genes in the Hox cluster diagrams shown in b. Anterior is to the left, dorsal is at the top. b | A schematic of the Hox gene clusters (not to scale) in the genomes of Caenorhabditis elegans, D. melanogaster and M. musculus. Genes are coloured to differentiate between Hox family members, and genes that are orthologous between clusters and species are labelled in the same colour. In some cases, orthologous relationships are not clear (for example, lin-39 in C. elegans). Genes are shown in the order in which they are found on the chromosomes but, for clarity, some non-Hox genes that are located within the clusters of nematode and fly genomes have been excluded. The positions of three non-Hox homeodomain genes, zen, bcd and ftz, are shown in the fly Hox cluster (grey boxes). Gene abbreviations: ceh-13, C. elegans homeobox 13; lin-39, abnormal cell lineage; mab-5, male abnormal 5; egl-5, egg-laying defective 5; php-3, posterior Hox gene paralogue 3; nob-1, knob-like posterior; lab, labial; pb, proboscipedia; zen, zerknullt; bcd, bicoid; Dfd, Deformed; Scr, Sex combs reduced; ftz, fushi tarazu; Antp, Antennapedia; Ubx, Ultrabithorax; abd-A, abdominal-A; Abd-B, Abdominal-B. c | A compilation of in vivo DNA binding sequences arranged by the structural type of homeodomain that is encoded by the Hox genes. The three classes are Labial, Central, and Abdominal-B. The listed DNA binding sequences that are bound by Hox monomers and Pre-B-cell homeobox/CEH20 (PBC)–Hox heterodimers are those that are required for the function of one or more Hox-response elements in developing mouse36, 92, 101, 102, 103, 104, 105, 106, fly28, 36, 44, 45, 46, 51, 52, 53, 54, 95, 100, 107, 108, 109, 110, 111 or nematode29, 112. As no known HOX1-monomer-binding (mouse) or LAB-monomer-binding (fly) sites have been found to be functional in vivo, only PBC–LAB-heterodimer-binding sites are shown. Consensus logos were generated using all verified Hox-binding sites with WEBLOGO113. 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. 32-3 Individual choanoflagellate Choanoflagellates OTHER EUKARYOTES Sponges Animals Collar cell (choanocyte) Other animals 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 monophyletic group Fig. 32-6 100 µm RESULTS Site of gastrulation Site of gastrulation Symmetry • Animals can be categorized according to the symmetry of their bodies, or lack of it • Some animals have radial symmetry Fig. 32-7 (a) Radial symmetry (b) Bilateral symmetry 精子和卵子各帶一半染色體進行受精作用 II. Animal Development A. Fertilization B. Cleavage C. Gastrulation D. Neurulation E. Extraembryonic Membranes F. Human Development Cleavage Figure 2-11: Events during the first week of human development. 1, Oocyte immediately after ovulation. 2, Fertilization, approximately 12 to 24 hours after ovulation. 3, Stage of the male and female pronuclei. 4, Spindle of the .rst mitotic division. 5, Twocell stage (approximately 30 hours of age). 6, Morula containing 12 to 16 blastomeres (approximately 3 days of age). 7, Advanced morula stage reaching the uterine lumen (approximately 4 days of age). 8, Early blastocyst stage (approximately 4.5 days of age). The zona pellucida has disappeared. 9, Early phase of implantation (blastocyst approximately 6 days of age). The ovary shows stages of transformation between a primary follicle and a preovulatory follicle as well as a corpus luteum. The uterine endometrium is shown in the progestational stage. Amnion becomes filled with amniotic fluid Yolk sac becomes part of the gut, earliest blood cells Allantois constructs umbilical cord linking embryo to placenta and part of urinary bladder Chorion helps form placenta and is the outermost membrane which encloses the embryonic body Gastrulation Ectoderm: Epidermis Epithelia of oral and nasal cavities Nervous system Lens and cornea Inner ear Mesoderm: Dermis Muscle Skeleton (bone and cartilage and muscle) Circularatory system Organs of urogenital system Kidneys Outer (body cavity) layers of digestive and respiratory tracts Endoderm Epithelium of digestive and respiratory tracts Liver Pancreas Specialisation of endoderm • • • • • • • Forms all body parts except: • Nervous • Skin • Epidermal derivatives • Epithelial and glandula derivates of mucosa 1st evidence of mesodermal differentiation is appearance of notochord Aggregates form either side of notochord e.g. somites Around those are the intermediate mesoderm and lateral mesoderm Each somite has 3 functional parts: • Sclerotome - forms vertebrae and ribs • Dermatome - forms dermis of skin in dorsal part of body • Myotome - forms skeletal muscles of neck, body trunk, limbs Intermediate mesoderm - forms gonads, kidneys and adrenal cortex Lateral mesoderm: • Somatic - forms dermis of skin in ventral body region and limb buds • Splanchic - forms cardiovascular system, organs and most connective tissue Specialisation of the Mesoderm • • The ectoderm germ layer forms a variety of structures in the body. By far the most complicated and interesting structure formed from the ectoderm is the nervous system. From the established ectoderm layer of the gastrula, neural tissue is derived by a series of tissue inductions, movements, and differentiations. There are a huge number of proteins, genes, and other factors which take part in this complex process. New differentiation factors are discovered each day. This site will only cover a few primary factors. The general differentiation of the neural tissue starts with the notochord. The notochord (derived from the mesoderm) is the primary inducer of the neural plate. Two signaling molecules, noggin and chordin, which are released by the notochord, induce the overlying ectoderm to thinken into the neural plate. The two molecules both function by blocking the action of bone morphogenic protein-4 (BMP-4). BMP-4 is also critical in mesodermic and hematopoietic development. It inhibits ectoderm from differentiating to neural plate tissue. This in vivo action has been reproduced in in vitro experiments. Under these conditions, the neural plate develops forebrain characteristics. Neural ectoderm induced in the presence of Fibroblast Growth Factor-8 (FGF-8) will develop more caudal features of the spinal chord. FGF's also play a role in liver development. Along the length of the neural tube, neuroepithelial cells proliferate. Within this neuroepithelium exist multipotential stem cells of the nervous system. During the development of the embryo, these ES cells differentiate into a variety of cell lineages which eventually give rise to the multiple types of mature cells of the adult nervous system (see photo below). Many of these stem cells are only found in certain areas of the developing nervous system. As they begin to differentiate, certain cells must migrate from these primordial locations to the proper location of the adult cell. Of particular interest is the O-2A progenitor cell lineage because it gives rise to oligodendrocytes and type-2 astrocytes. Ectoderm Mesoderm Endoderm skin notochord lining of gut brain muscles lining of lungs spinal cord blood lining of bladder all other neurons bone liver sense receptors sex organs pancreas • The two lateral ends of the neural plate then fold up to meet at the midline of the gastrula to form the neural tube. (See photo above) A variety of genes give the tube a cranial/caudal polarity (see left photo) and guide the formation of the various structures of the nervous system. Another set of genes and signaling factors (most notably Slug and Sonic Hedgehog (Shh) ) establish the dorsal/lateral polarity also essential for proper formation of the nervous system. (See photo below) Module 1932: The Cell Differentiation and Development 1 Neurulation A: Embryonic disc accomplished gastrulation - ectoderm thickens B: Neural plate forms neural folds and neural groove C: Neural folds close D: Neural tube detached from surface ectoderm Critical Periods of Human Development Light blue bars indicate periods when organs are most sensitive to damage from alcohol, viral infection, etc. • Two-sided symmetry is called bilateral symmetry • Bilaterally symmetrical animals have: – – – – 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 • Ectoderm is the germ layer covering the embryo’s surface • Endoderm is 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 mesoderm layer; these include all bilaterians Body Cavities • Most triploblastic animals possess a body cavity • A true body cavity is called a coelom and is derived from mesoderm • Coelomates are animals that possess a true coelom Fig. 32-8 Coelom Digestive tract (from endoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) (a) Coelomate Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) (b) Pseudocoelomate Body covering (from ectoderm) Tissuefilled region (from mesoderm) Wall of digestive cavity (from endoderm) (c) Acoelomate Protostome and Deuterostome Development • Based on early development, many animals can be categorized as having protostome development or deuterostome development Cleavage • In protostome development, cleavage is spiral and determinate • In deuterostome development, cleavage is radial and 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 Fig. 32-9 Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderm, chordates) Eight-cell stage Eight-cell stage Spiral and determinate (a) Cleavage Radial and indeterminate (b) Coelom formation Key Coelom Ectoderm Mesoderm Endoderm Archenteron Coelom Mesoderm Blastopore Blastopore Solid masses of mesoderm split and form coelom. Mesoderm Folds of archenteron form coelom. Anus Mouth (c) Fate of the blastopore Digestive tube Mouth Mouth develops from blastopore. Anus Anus develops from blastopore. • One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons Fig. 32-10 “Porifera” Eumetazoa Metazoa ANCESTRAL COLONIAL FLAGELLATE Cnidaria Ctenophora Deuterostomia Ectoprocta Brachiopoda Echinodermata Bilateria Chordata Platyhelminthes Protostomia Rotifera Mollusca Annelida Arthropoda Nematoda • One hypothesis of animal phylogeny is based mainly on molecular data Metazoa Silicea Calcarea Ctenophora Eumetazoa ANCESTRAL COLONIAL FLAGELLATE “Porifera” Fig. 32-11 Cnidaria Acoela Bilateria Deuterostomia Echinodermata Chordata Platyhelminthes Lophotrochozoa Rotifera Ectoprocta Brachiopoda Mollusca Annelida Ecdysozoa Nematoda Arthropoda Fig. 32-13 Lophophore Apical tuft of cilia 100 µm Mouth (a) An ectoproct Anus (b) Structure of a trochophore larva Fig. 32-UN1 Common ancestor of all animals Metazoa Sponges (basal animals) Eumetazoa Ctenophora Cnidaria Acoela (basal bilaterians) Deuterostomia Bilateral summetry Three germ layers Lophotrochozoa Ecdysozoa Bilateria (most animals) True tissues