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CHAPTER 30: ANIMALS: PART I LECTURE OUTLINE 30.1 Evolutionary Trends Among Animals Animals are extremely diverse, but in general they are heterotrophic, typically have the power of movement or locomotion by means of muscle fibers, are multicellular, have a life cycle in which the adult is typically diploid, and undergo sexual reproduction and produce an embryo that goes through development stages. All but one of the 30 animal phyla is invertebrates. Only one phylum contains vertebrates. Level of Organization Three levels of organization exist in the animal kingdom: the cellular, tissue, and organ levels. Type of Body Plan Two body plans are observed in the animal kingdom: the sac plan and the tube-within-atube plan. Type of Symmetry Animals can be asymmetrical, radially symmetrical, or bilaterally symmetrical. Type of Body Cavity The body cavity that contains internal organs is often called a coelom. Animals can be acoelomate, have a pseudocoelom, or have a true coelom. Segmentation Segmentation is the repetition of body parts along the length of the body. Animals can be nonsegmented or segmented. Jointed Appendages In arthropods, jointed appendages provide a means of locomotion. 30.2 Introducing the Invertebrates Sponges: Multicellular Sponges are aquatic. They are multicellular but lack organized tissues. They are filter feeders. Sponges can reproduce both asexually and sexually. Cnidarians: True Tissues Cnidarians are multicellular, tubular, or bell-shaped animals that reside mainly in shallow coastal waters. They are radially symmetrical. Examples include sea anemone, cup coral, Portuguese man-of-war, and jellyfish. They have specialized stinging cells called cnidocytes. Hydra Hydra is a freshwater cnidarian. It has a sac body plan. It has two tissue layers: ectoderm and endoderm. Flatworms: Bilateral Symmetry Flatworms have bilateral symmetry. They also have three germ layers. They are acoelomates. Planarians Freshwater planarians are small, literally flat, worms. They have an excretory and a nervous system. Parasitic Flatworms The parasitic flatworms include the tapeworms and the flukes. Tapeworms Tapeworms are endoparasites of various vertebrates, including humans. They attach to the intestinal wall of the host and feed. Flukes Flukes are all endoparasites of various vertebrates. They are usually named for the type of vertebrate organ they inhabit. Roundworms: Pseudocoelomates Roundworms have a tube-within-a-tube body plan and a body cavity. The body cavity is a pseudocoelom. They have a hydrostatic skeleton and are nonsegmented. Ascaris A female Ascaris is very reproductively prolific. They are most commonly parasites of humans and pigs. Other Roundworms Trichinosis is a fairly serious infection cause by eating pork that is not fully cooked that contains encysted larvae of the round worm Trichinella spiralis. Elephantiasis is caused by a roundworm called the filarial worm. Pinworm and hookworm infections are more common in the United States. 30.3 Molluscs: Coelomates The mollusks and all the other species we will study are coelomates. They have bilateral symmetry, three germ layers, the organ level of organization, and a tube-within-a-tube body plan. Unique Characteristics of Molluscs All molluscs have a body composed of at least three parts: the visceral mass, the foot, and the mantle. Gastropods Gastropods include nudibranchs, conchs, and snails. The foot is ventrally flattened. Cephalopods Cephalopods include octopuses, squid, and nautiluses. The foot has evolved into tentacles about the head. Bivalves Bivalves include clams, mussels, oysters, and scallops. Their shells have two parts. The Visceral Mass The clam has an open circulatory system and a heart. It also has a nervous system and a digestive system. Comparison Refer to Table 30.2 for a comparison of a clam, squid, and land snail. 30.4 Annelids: Segmented Worms Annelids are segmented. Internally, the segments are partitioned by septa. They have a hydroskeleton, a closed circulatory system, a ventral solid nerve cord, and nephridium. Polychaetes Most annelids are marine organisms. They have many setae or bristles that anchor the worm or help it move. Oligochaetes The oligochaetes, which include earthworms, have few setae per segment. Segmentation Segmentation is evidenced by body rings, coelom divided by septa, setae on most segments, ganglia and lateral nerves in each segment, nephridia in most segments, and branch blood vessels in each segment. Reproduction Earthworms are hermaphroditic. Comparison with Clam Worm The comparison of the marine clam worm with the terrestrial earthworm highlights the manner in which earthworms are adapted to life on land. Leeches Leeches have no setae and each body ring has several transverse grooves. Among their modifications are two suckers. 30.5 Arthropods: Jointed Appendages Arthropods are extremely diverse. Over one million species have been discovered and described. Arthropods have jointed appendages and an exoskeleton made of chitin. They are segmented and have a well-developed nervous system that includes a brain and a ventral solid nerve cord. Crustaceans Crustaceans include barnacles, shrimps, lobsters, and crabs. They are named for their hard shells. Internal Organs In the crayfish, the digestive system includes a stomach. The coelom is reduced to a space around the reproductive system. They have an open circulatory system. The nervous system is very similar to that of an earthworm. Insects Insects are very numerous and diverse. Insects have a body that is divided into a head, a thorax, and an abdomen. The head bears sensory antennae, a pair of compound eyes, and several simple eyes. The mouthparts are adapted for the type of food. Wings may be present. Internal Organs In the grasshopper, there is an excretory system, a respiratory system, and a circulatory system. Reproduction and Development Metamorphosis is a change in form and physiology that occurs as an immature stage, called a larva, becomes an adult. Comparison with Crayfish A comparison of a grasshopper with a crayfish reveals the adaptations to a terrestrial environment. Arachnids The arachnids include scorpions, spiders, ticks, and mites. They have six pairs of appendages.