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Comparing Key Groups
Evolutionary trends toward • Greater size • Compartmentalization (division of labor among
cells, tissues, and organs)• Integration of specialized activities that keep the
organism alive
Body Organization
Cephalization • Sensory cells concentrated at the head
Segmentation• Repetition of body units, front-to-back
Key Concepts: INTRODUCING THE ANIMALS
Animals • Multicelled heterotrophs (ingest other organisms) • Grow and develop through a series of stages• Actively move about during all or part of life cycle
Cells of most animals form tissues and extracellular matrixes
Sponges (Phylum Porifera)
Sponges• No symmetry, tissues, or organs • Flattened cells line the body wall (many pores;
spikes of silica and/or proteins)• Filter feeders (flagellated collar cells absorb food;
amoeboid cells digest and distribute it)• Zygote develops into free-living larva
Cnidarians (Phylum Cnidaria)
Jellyfishes, corals, and sea anemones• Radial, tentacled carnivores• Gastrovascular cavity (respiration and digestion)• True epithelial tissues with a jellylike matrix in
between• Simple nervous system
Flatworms (Phylum Platyhelminthes)
Free-living turbellarians (planarians), parasitic tapeworms and flukes• Simplest animals with organ systems• Paired nerve cords
Annelids
Segmented worms (earthworms, polychaetes) and leeches• Closed circulatory system• Digestive and excretory systems• Nervous system, ganglia in each segment • Muscles and fluid in chambers act as a
hydrostatic skeleton
Mollusks (Phylum Mollusca)
Including gastropods (snails), bivalves (scallops), chitons, nudibranchs, cephalopods • 100,000 named species
Cephalopods
The fastest (squids), largest (giant squids), and smartest (octopuses) invertebrates
Have a mantle • Sheetlike part of the body mass, draped back on
itself
Roundworms (Phylum Nematoda)
More than 22,000 kinds of roundworms• Free-living decomposers or parasites• Some agricultural pests and human parasites• Cylindrical body with bilateral features• A complete gut• Organ systems in a false coelom
Key Concepts: BILATERAL INVERTEBRATES
Most animals show bilateral symmetry
Bilateral animals have tissues, organs, and organ systems
All adult tissues arise from two or three simple layers that form in early embryos
Arthropod Characteristics
Key arthropod adaptations• Hardened exoskeleton • Jointed appendages • Specialized and fused segments (wings)• Efficient respiratory and sensory structures (eyes,
antennae)
Chelicerates
Horseshoe crabs and arachnids (spiders, scorpions, ticks, and mites)• Predators, parasites, or scavengers
Echinoderms
Sea stars, sea urchins, sea cucumbers, etc.• Exoskeleton with spines, spicules, or plates of
calcium carbonate • Water-vascular system with tube feet• Adults are radial, but bilateral traits appear in
larval stages
Chordate Heritage
Four features define chordates • A notochord • A dorsal hollow nerve cord • A pharynx with gill slits• A tail extending past the anus
All features form in embryos• May or may not persist in adults
Craniates
Chordates with a braincase of cartilage or bone • Hagfish (jawless fish): Simplest modern craniate
Vertebrate Evolution
Key innovations laid the foundation for adaptive radiations of vertebrates• Vertebral column of cartilaginous or bony
segments • Jaws evolved in predatory fishes• Gills evolved in water, then lungs for dry land• Paired fins were a starting point for other limbs
Gill-Supporting Structures
Key Concepts: TRENDS AMONG VERTEBRATES
In some vertebrate lineages, a backbone replaced the notochord as the partner of muscles used in motion
Jaws evolved, sparking the evolution of novel sensory organs and brain expansions
On land, lungs replaced gills, and more efficient blood circulation enhanced gas exchange
Fleshy fins with skeletal supports evolved into limbs, now typical of vertebrates on land
Jawed Fishes and Tetrapods
Jawed fishes• Cartilaginous fishes (sharks and rays)• Bony fishes
Body plans adapted to life in water• Streamlined shape reduces drag • Swim bladder (in bony fishes) adjusts buoyancy
Bony Fishes
The most diverse vertebrates• Lungfishes • Lobe-finned fishes (coelacanth)• Ray-finned fishes
Amphibians
Frogs, toads, and salamanders• Carnivorous vertebrates• Adapted to life on land (lungs, 3-chambered
heart)• Nearly all return to the water to reproduce
Amniotes
First vertebrates able to complete their life cycle on dry land• Water-conserving skin and kidneys• Amniote eggs (four membranes)• Active life-styles
Dinosaur Extinctions
K-T asteroid impact hypothesis• A huge asteroid impact caused extinction of last
dinosaurs; spared earliest birds and mammals
Modern Reptiles
Major Groups• Turtles (shell attached to skeleton)• Lizards (the most diverse reptiles)• Snakes (limbless)• Crocodilians (closest relatives of birds)
Reptile Characteristics
General characteristics• Live on land or in water• Cold-blooded• Have a cloaca (opening for wastes and
reproduction) • Eggs are fertilized in the body, usually laid on
land
Fig. 24.16, p.396
cloaca
olfactory lobe(sense of smell)
hindbrain, midbrain,forebrain
spinalcord
vertebral column gonad
kidney (control of water,solute levels in internalenvironment)
unmatched rowsof teeth on upperand lower jaws
snout
stomachesophagus lung heart liver intestine
Adaptations for Flight and Migration
Feathers, lightweight bones, and highly efficient respiratory and circulatory systems
Mammals
Animals with hair, females that nourish young with milk from mammary glands, a single lower jawbone and four kinds of teeth
Modern Mammals
Three major lineages• Egg-laying mammals (monotremes)• Pouched mammals (marsupials)• Placental mammals, the most diverse and
widespread mammals
Primate Evolution
Key trends• Better daytime vision• Upright walking (bipedalism)• More refined hand movements• Smaller teeth• Bigger brains• Social complexity (extended parental care;
culture evolved in some lineages)
Early Humans
Humans (Homo) arose 2 million years ago• H. habilis was an early toolmaking species • H. erectus dispersed into Europe and Asia
Emergence of Modern Humans
Extinct Neandertals and modern humans are close relatives with distinct gene pools
Modern H. sapiens evolved 195,000 years ago