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Chapter 18 The Evolution of Animal Diversity What Am I? ◦ Of some 1.5 million species of organisms known to science Over two-thirds are animals ◦ Humans have a long history of studying animal diversity But classifying an animal isn’t always easy ◦ Imagine you were the first person to encounter the animal pictured here With all of its varying characteristics, what would you think it is? ◦ Biologists often encounter classification problems When evolution creates organisms with similar characteristics A Tasmanian tiger, 1928 What is an animal? ◦ Animals are eukaryotic, multicellular heterotrophs That ingest their food Figure 18.1A ANIMAL EVOLUTION AND DIVERSITY ◦ Animal development ◦ May include a blastula, gastrula, and larval stage Key Haploid (n) Sperm Diploid (2n) 2 1 Meiosis Adult 8 Egg Zygote (fertilized egg) 3 Eight-cell stage Metamorphosis 4 Blastula (cross section) Digestive tract Ectoderm Larva 7 Endoderm Figure 18.1B Internal sac 5 Early gastrula (cross section) 6 Future Later gastrula mesoderm (cross section) The ancestor of animals was probably a colonial, flagellated protist ◦ Cells in these protists Gradually became more specialized and layered Somatic cells Digestive cavity Reproductive cells 1 Colonial protist, an aggregate of identical cells Figure 18.2A 2 Hollow sphere of unspecialized cells (shown in cross section) 3 Beginning of cell specialization (cross section) 4 Infolding (cross section) 5 Gastrula-like “proto-animal” (cross section) ◦ Animal diversity exploded during the Cambrian period Figure 18.2B Animals can be characterized by basic features of their “body plan” ◦ Animal body plans may vary in symmetry Top Dorsal surface Anterior end Posterior end Ventral surface Figure 18.3A Bottom Tissue-filled region (from mesoderm) Vary in body cavity Body covering (from ectoderm) Digestive tract (from endoderm) Body covering (from ectoderm) Muscle layer (from mesoderm) Digestive tract (from endoderm) Pseudocoelom Coelom Figure 18.3B–D Digestive tract (from endoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Development as either protostomes or deuterostomes Together these animals show bilateral symmetry and three germ layers Distinction between each is found in embryonic development Deuterostomes Figure 18.4 Eumetazoans True tissues Ancestral colonial protist Nematodes Arthropods Annelids Protostomes Bilaterians Bilateral symmetry Radial symmetry No true tissues Molluscs Flatworms Chordates Echinoderms Cnidarians Sponges The body plans of animals can be used to build phylogenetic trees ◦ One hypothesis of animal phylogeny is based on morphological comparisons Invertebrates Sponges have a relatively simple, porous body ◦ Sponges, phylum Porifera Are the simplest animals and have no true tissues Figure 18.5A–C INVERTEBRATES ◦ Flagellated choanocytes Filter food from the water passing through the porous body Pores Choanocyte Amoebocyte Skeletal fiber Central cavity Figure 18.5D Choanocyte in contact with an amoebocyte Water flow Flagella Cnidarians are radial animals with tentacles and stinging cells ◦ Cnidarians, phylum Cnidaria Have true tissues and radial symmetry ◦ Their two body forms are Polyps, such as hydra Medusae, the jellies Figure 18.6A–C ◦ They have a gastrovascular cavity And cnidocytes on tentacles that sting prey Capsule (nematocyst) Coiled thread Tentacle “Trigger” Discharge of thread Prey Cnidocyte Figure 18.6D Flatworms are the simplest bilateral animals ◦ Flatworms, phylum Platyhelminthes Are bilateral animals with no body cavity ◦ A planarian has a gastrovascular cavity And a simple nervous system Gastrovascular cavity Nerve cords Planaria Mouth Eyespots Nervous tissue clusters Figure 18.7A Bilateral symmetry ◦ Flukes and tapeworms Are parasitic flatworms with complex life cycles Figure 18.7B Colorized SEM 80 Units with reproductive structures Hooks Sucker Scolex (anterior end) Nematodes have a pseudocoelom and a complete digestive tract ◦ Nematodes, phylum Nematoda Have a pseudocoelom and a complete digestive tract Are covered by a protective cuticle ◦ Many nematodes are free-living And others are plant or animal parasites Muscle tissue Figure18.8A, B LM 350 Mouth Colorized SEM 400 Trichinella juvenile Diverse molluscs are variations on a common body plan ◦ All molluscs have a muscular foot and a mantle Which may secrete a shell that encloses the visceral mass ◦ Many mollusks ◦ Feed with a rasping radula Visceral mass Coelom Heart Kidney Mantle Reproductive organs Digestive tract Shell Digestive tract Mantle cavity Radula Anus Gill Mouth Foot Figure 18.9A Nerve cords Radula Mouth Gastropods ◦ Gastropods are the largest group of molluscs And include the snails and slugs Figure 18.9B, C Bivalves ◦ The bivalves have shells divided into two halves And include clams, oysters, mussels, and scallops Figure 18.9D Cephalopods ◦ Cephalopods are adapted to be agile predators And include squids, cuttlefish and octopuses Figure 18.9E, F Annelids are segmented worms ◦ The segmented bodies of phylum Annelida Give them added mobility for swimming and burrowing Earthworms and Their Relatives ◦ Earthworms Eat their way through soil Have a closed circulatory system Anus Circular muscle Epidermis Segment wall Longitudinal muscle Dorsal vessel Mucus-secreting organ Dorsal Coelom vessel Brain Segment wall (partition between segments) Excretory organ Bristles Intestine Excretory organ Digestive tract Nerve cord Bristles Ventral vessel Segment wall Blood vessels Mouth Figure 18.10A Nerve cord Pumping segmental vessels Giant Australian earthworm Polychaetes Form the largest group of annelids Search for prey on the seafloor or live in tubes and filter food particles Figure 18.10B, C Leeches ◦ Most leeches Are free-living carnivores, but some suck blood Figurer 18.10D Arthropods are segmented animals with jointed appendages and an exoskeleton ◦ The diversity and success of arthropods is largely related to their segmentation, exoskeleton, and jointed appendages Cephalothorax Abdomen Antennae (sensory reception) Thorax Head Swimming appendages Figure 18.11A Walking legs Pincer (defense) Mouthparts (feeding) Chelicerates ◦ Chelicerates include Colorized SEM 900 Horseshoe crabs Arachnids, such as spiders, scorpions, mites, and ticks A black widow spider (about 1 cm wide) A scorpion (about 8 cm long) Figure 18.11B, C A dust mite (about 420 µm long) Millipedes and Centipedes ◦ Millipedes and centipedes Are identified by the number of jointed legs per body segment Figure 18.11D Crustaceans ◦ The crustaceans Are nearly all aquatic Include crabs, shrimps, and barnacles Figure 18.11E Insects are the most diverse group of organisms ◦ Insects have a three-part body consisting of Head, thorax, and abdomen Three sets of legs Wings (most, but not all insects) ◦ Many insects undergo Incomplete or complete metamorphosis A. Order Orthoptera ◦ The order orthoptera includes Grasshoppers, crickets, katydids, and locusts Head Antenna Thorax Abdomen Forewing Eye Mouthparts Figure 18.12A Hindwing B. Order Odonata ◦ The order odonata includes ◦ Dragonflies and damselflies Figure 18.12B C. Order Hemiptera ◦ The order hemiptera includes Bedbugs, plant bugs, stinkbugs, and water striders Figure 18.12C D. Order Coleoptera ◦ The order coleoptera includes Beetles Figure 18.12D E. Order Lepidoptera ◦ The order lepidoptera includes ◦ Moths and butter flies Figure 18.12E F. Order Diptera ◦ The order Diptera includes Flies, fruit flies, houseflies, gnats, and mosquitoes Haltere Figure 18.12F G. Order Hymenoptera ◦ The order hymenoptera includes Ants, bees, and wasps Figure 18.12G Echinoderms have spiny skin, an endoskeleton, and a water vascular system for movement ◦ Echinoderms, phylum Echinodermata Includes organisms such as sea stars and sea urchins Are radially symmetrical as adults Tube foot Tube foot Figure 18.13B, C Spine ◦ The water vascular system Has suction cup–like tube feet used for respiration and locomotion Anus Spines Stomach Tube feet Canals Figure 18.13A Our own phylum, Chordata, is distinguished by four features: ◦ The simplest chordates are tunicates and lancelets Marine invertebrates that use their pharyngeal slits for suspension feeding Excurrent siphon Dorsal, hollow nerve cord Post-anal tail Head Pharyngeal slits Mouth Notochord Mouth Muscle segments Notochord Pharynx Pharyngeal slits Digestive tract Water exit Adult (about 3 cm high) Figure 18.14A, B Larva Segmental Anus muscles Dorsal, hollow nerve cord Post-anal tail Derived characters define the major clades of chordates Chordates Craniates Vertebrates Jawed vertebrates Mammals Reptiles Amphibians Lobe-fins Ray-finned fishes Tetrapods Amniotes Sharks, rays Lampreys Hagfishes Lancelets A chordate phylogenetic tree Is based on a sequence of derived characters Tunicates ◦ Amniotic egg Legs Lobed fins Lungs or lung derivatives Jaws Vertebral column Head Figure 18.15 Brain Ancestral chordate VERTEBRATES Milk ◦ Most chordates are vertebrates With a head and a backbone made of vertebrae Lampreys are vertebrates that lack hinged jaws ◦ Lampreys lack hinged jaws and paired fins Figure 18.16A ◦ Most vertebrates have hinged jaws Which may have evolved from skeletal supports of the gill slits Gill slits Skeletal rods Skull Mouth Figure 18.16B Jawed vertebrates with gills and paired fins include sharks, ray-finned fishes, and lobe-fins ◦ Three lineages of jawed vertebrates with gills and paired fins Are commonly called fishes Chondrichthyans ◦ Chondrichthyans Have a flexible skeleton made of cartilage Include sharks and rays Figure 18.17A Ray-finned Fishes (e.g. Atlantic herring, Ocean sunfish) ◦ The ray-finned fishes have A skeleton reinforced with a hard matrix of calcium phosphate Operculi that move water over the gills Bony skeleton A buoyant swim Dorsal fin Gills bladder Operculum Pectoral fin Heart Rainbow trout, a ray-fin Figure 18.17B Anal fin Swim bladder Pelvic fin Lobe-fins (e.g. coelacanths, lungfish) ◦ The lobe-fin fishes Have muscular fins supported by bones Figure 18.17C Amphibians were the first tetrapods—ver tebrates with two pairs of limbs ◦ Amphibians Were the first tetrapods with limbs allowing movement on land Bones supporting gills Figure 18.18A Tetrapod limb skeleton Include frogs, toads, salamanders, and caecilians Figure 18.18B–D Most amphibian embryos and larvae still must develop in water Reptiles are amniotes—tetrapods with a terrestrially adapted egg ◦ Terrestrial adaptations of reptiles include Waterproof scales A shelled, amniotic egg Figure 18.19A, B ◦ Living reptiles other than birds are ectothermic ◦ Dinosaurs, the most diverse reptiles to inhabit land Included some of the largest animals ever to inhabit land May have been endothermic, producing their own body heat Figure 18.19C Birds are feathered reptiles with adaptations for flight ◦ Birds evolved from A lineage of small, two-legged dinosaurs called theropods Wing claw (like dinosaur) Figure 18.20A Teeth (like dinosaur) Long tail with many vertebrae Feathers (like dinosaur) ◦ Birds are reptiles that have Wings, feathers, endothermic metabolism, and many other adaptations related to flight Figure 18.20B ◦ Flight ability is typical of birds But there are a few flightless species Figure 18.20C Mammals are amniotes that have hair and produce milk ◦ Mammals are endothermic amniotes with Hair, which insulates their bodies Mammary glands, which produce milk Mammals ◦ Monotremes lay eggs Figure 18.21A •Monotremes lay eggs ◦ The embryos of marsupials and eutherians are nurtured by the placenta within the uterus ◦ Marsupial offspring complete development attached to the mother’s nipple, usually inside a pouch Figure 18.21B ◦ Eutherians, placental mammals Complete development before birth Figure 18.21C ANIMAL PHYLOGENY AND DIVERSITY REVISITED An animal phylogenetic tree is a work in progress ◦ Molecular-based phylogenetic trees Deuterostomes Arthropods Nematodes Annelids Molluscs Flatworms Chordates Echinoderms Cnidarians Sponges Distinguish two protostome clades: the lophotrochozoans and the ecdysozoans Ecdysozoans Lophotrochozoans Bilaterians Radial symmetry Bilateral symmetry Eumetazoans No true tissues True tissues Figure 18.22 Ancestral colonial protist Humans threaten animal diversity by introducing non-native species ◦ Introduced species Are threatening Australia’s native animals Figure 18.23A-D CONNECTION