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Phylum Cnidaria: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes Two layers of cells that form TISSUES - cells that act as a functional unit Gastrovascular cavity that allows for extracellular digestion - large food particles broken down so that the gastrodermis can do intracellular digestion. Simple nerve net forms nervous system - no brain 1. Phylum Platyhelminthes: Flatworms are acoelomates with gastrovascular cavities • There are about 20,000 species of flatworms living in marine, freshwater, and damp terrestrial habitats. – They also include many parasitic species, such as the flukes and tapeworms. • Flatworms and other bilaterians are triploblastic, with a middle embryonic tissue layer, mesoderm, which contributes to more complex organs and organs systems and to true muscle tissue. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Two way gut ventral nerve cords Cephalization - brain, eye spot at head gastrovascular cavity acoelomate 5. Phylum Mollusca: Mollusks have a muscular foot, a visceral mass, and a mantle • The phylum Mollusca includes 150,000 known species of diverse forms, including snails and slugs, oysters and clams, and octopuses and squids. • Most mollusks are marine, though some inhabit fresh water, and some snails and slugs live on land. • Mollusks are soft-bodied animals, but most are protected by a hard shell of calcium carbonate. – Slugs, squids, and octopuses have reduced or lost their shells completely during their evolution. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Mantle secretes the shell Radula is used for rasping food off of surfaces, but can be modified to bore holes or tear apart tough animal tissue Has trochophore larvae a type of ciliated larvae They lack true segmentation Gastropoda is the largest molluscan class During embryonic development it undergoes torsion which results in its asymmetrical shape bivalves Annelids have a true coelom - which allows for easier fluid movement between organs They have body segmentation - each segment can become specialized closed circulatory system with hearts- blood with hemoglobin excretory tubes called metanephridia collects wastes from the blood through a funnel called a nephrostome and dumps it outside through nephridia pores. Phylum Nematoda: Roundworms are nonsegmented pseudocoelomates covered by tough cuticles complete digestive tract BLASTULA invagination GASTRULA Forms mouth in protostomes NEURULA Arthropods are segmented coelomates with exoskeletons and jointed appendages The diversity and success of arthropods is largely due to three features: body segmentation, a hard exoskeleton, and jointed appendages. Crustaceans Spiders have cheicerae - piercing mouth parts a pair of appendages called pedipalps used for sensing or feeding four pairs of walking legs book lungs used for gas exchange Insecta is the largest class 3 body parts with 3 pairs of legs two pair of wings nitrogenous waste excreted through Malpighian tubules gas exchange through tracheal tubes mandibles (jaws) Echinoderms Coelomates Echinoderms have water entering into a madreporite down a water vascular system that operates tube feet Deuterostomes Radial Symmetry They are capable of everting their stomach through their mouth - either dumping the contents or digesting something outside of its body • The phylum Chordata includes three subphyla, the vertebrates and two phyla of invertebrates, the urochordates and the cephalochordates. Fig. 34.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 1. Four anatomical features characterize the phylum Chordata • Although chordates vary widely in appearance, all share the presence of four anatomical structures at some point in their lifetime. – These chordate characteristics are a notochord; a dorsal, hollow nerve cord; pharyngeal slits; and a muscular, postanal tail. Fig. 34.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Ectoderm will invaginate to form the spinal cord and brain Cells from the neural crest may form bone and cartilage of the skull Notochord will evolve into the vertebrae of the backbone SuperClass Agnatha Brain and cranium evolved notochord will evolve into vertebrae of backbone Jawless fish - mud suckers, suspension feeders or parasitic no paired fins include lamprey and hagfish Jaws and paired fins were major evolutionary breakthroughs Jaws evolved from a pair of gill support bars A jawed fish can exploit food supplies that were unavailable to earlier agnathans The Devonian period (about 360 to 400 million years ago) has been called the “age of fishes”. Chondircthyes Sharks and rays have cartilaginous endoskeleton Jaws gill slits paired fins The intestine of shark is a spiral valve, a corkscrew-shaped ridge that increases surface area and prolongs the passage of food along the short digestive tract. The lateral line system, a row of microscopic organs sensitive to pressure changes, can detect low frequency vibrations •The ancestors of Chondrichthyes had bony skeletons. •The cartilaginous skeleton evolved secondarily. Osteichthyes Bony or calcified endoskeleton with skull (During the development of most vertebrates, the skeleton is first cartilaginous and then becomes ossified as hard calcium phosphate matrix replaces the rubbery matrix of cartilage) operculum covers the gills swim bladder controls the bouyancy swim bladder evolved from balloonlike lungs that may have been used to breath air when dissolved oxygen levels were low in stagnant shallow waters ray finned fish, lobe finned fish, lung fish •Traditionally, all bony fishes were combined into a single class, Osteichthyes, but most systematists now recognize three extant classes: the ray-finned fishes, the lobe-finned fishes, and the lungfishes. Amphibians adaptations for terrestrial living included hard endoskeleton for support a three chambered heart for more efficient circulation lungs for breathing air legs for movement on land They are not true terrestrial organisms because: the sideward limbs (not under body) did not support their weight their skin dried out and their gametes and eggs dried out The amnion provides a protective fluid environment for the embryo to develop in Reptiles can lay eggs in very dry environments Aves probably arose from a reptile An ancestral amniote gave rise to Reptiles, Aves and Mammals Reptiles are true terrestrial organisms because they have: scales on their skin to prevent dessication internal fertilization leathery or hard shell to prevent the eggs from drying out amniotic eggs Low pressure to body High Mammalian Characteristics • Evolved from therapsids • Hair (made of keratin) • Mammary Gland • Endothermic (active) • diaphragm • 4 chambered heart/high metabolism • most placental Evolutionary Trends from Ape To Humans • Jaw became shorter and teeth smaller • Point of attachment of the vertebra to the cranium shifted from the rear to the bottom-for bipedal walking • Braincase became larger • Feet Flattened and arch developed • Big toe moved in line • Reduced Size Differences Between the Sexes. In hominoids, a size difference between females and males is a major feature of sexual dimorphism. Evolutionary Trends from Ape To Humans • Eyebrow ridges and other keels on the skull were reduced • Nose becomes more prominent • Arms become shorter