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Unit 4, Part 1: Animal Diversity CHAPTER 30: ANIMALS: PART I 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. Anatomical Data Refer to Figure 30.2. Type of Symmetry Animals can be asymmetrical, radially symmetrical, or bilaterally symmetrical. Embryonic Development Sponges have the cellular level of organization. True tissues appear in the other animals as they undergo embryological development. Some animals have two germ layers (ectoderm and endoderm), while some have three (ectoderm, endoderm, and mesoderm). Animals with three germ layers are either protostomes or deuterostomes. 30.2 Introducing the Invertebrates Sponges Sponges are aquatic. They are multicellular but lack organized tissues. They are filter feeders. Sponges can reproduce both asexually and sexually. Cnidarians Cnidarians are multicellular, tubular, or bell-shaped animals that reside mainly in shallow coastal waters. They are radially symmetrical and have true tissues. Cnidarian Diversity Examples of cnidarians include sea anemone, coral, hydrozoans, and jellyfish. Hydra Hydra is a freshwater cnidarian. It has a sac body plan. It has two tissue layers: ectoderm and endoderm. 30.3 The Trochozoa The trochozoa are bilaterally symmetrical at least in some stage of their development. As embryos, they have three germ layers, and as adults, they have the organ level of organization. Trochozoans are protostomes and include the trochophores, which either have a trochophore larva today or an ancestor with one in the past. Flatworms Flatworms have bilateral symmetry. They also have three germ layers. They are acoelomates. Free-Living Flatworms 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 1 Flukes are all endoparasites of various vertebrates. They are usually named for the type of vertebrate organ they inhabit. Rotifers Rotifers are related to the flatworms and both are trochozoans. Rotifers have a crown of cilia, known as the corona, on their heads. Molluscs Molluscs include chitons, limpets, slugs, snails, abalones, conchs, nudibranchs, clams, scallops, squid, and octopuses. They have a true coelom, bilateral symmetry, three germ layers, the organ level of organization, and a complete digestive tract. 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 a funnel or siphon 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. Annelids Annelids are segmented, have a hydrostatic skeleton, and specialization of the digestive tract. Polychaetes Marine annelids are the Polychaeta, which refers to the presence of many setae. Setae are 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. 30.4 The Ecdysozoa The ecdysozoans are protostomes, as are the trochozoa. The term ecdysis means molting, and both roundworms and arthropods, which belong to this group, periodically shed their outer covering. Roundworms 2 Roundworms are nonsegmented worms that are prevalent in almost any environment. They possess a pseudocoelom. 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. Arthropods 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. They have a variety of respiratory organs and have reduced competition through metamorphosis. 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. CHAPTER 31: ANIMALS: PART II 31.1 Echinoderms Chordates are most closely related to the echinoderms as witnessed by their similar embryological development. Characteristics of Echinoderms Echinoderms are all marine animals. They have an endoskeleton and are often radially, not bilaterally, symmetrical. Echinoderm Diversity Echinoderms include sea lilies, feather stars, brittle stars, and sea cucumbers. Sea Stars 3 Sea stars have a five-rayed body with an oral and an aboral side. Locomotion depends on a water vascular system. They do not have a respiratory, excretory, or circulatory system. Sea stars reproduce both asexually and sexually. 31.2 Chordates To be classified as a chordate, an animal must have, at some time during its life history, a dorsal supporting rod called a notochord, a dorsal tubular nerve cord, pharyngeal pouches, and a postanal tail. Evolutionary Trends among the Chordates Several characteristics, including vertebrate, jaws, lungs, jointed appendages, a land existence, and reproduction suitable for land, distinguish each group of animals from the preceding one. Nonvertebrate Chordates In nonvertebrate chordates the notochord never becomes a vertebral column. Tunicates and lancelets are nonvertebrate chordates. 31.3 Vertebrates Vertebrates have a strong, jointed endoskeleton. The embryonic notochord is generally replaced by a vertebral column. A high degree of cephalization is accompanied by sense organs. Vertebrates have efficient respiration and excretion, and a closed circulatory system. Fishes: First Jaws, Then Lungs The first vertebrates were jawless fishes. Today there are three living groups of fishes: jawless fishes, cartilaginous fishes, and bony fishes. The latter two groups have jaws. Jawless Fishes Jawless fishes have smooth, scaleless skin and no jaws or paired fins. These include the hagfishes and lampreys. Cartilaginous Fishes Cartilaginous fishes include the sharks and the skates. They have skeletons of cartilage instead of bone. Bony Fishes Bony fishes are by far the most numerous and diverse of all the vertebrates. Bony fishes are divided into ray-finned and lobe-finned fishes. Amphibians: Jointed Appendages Amphibians live both on land and in the water. These include frogs, toads, newts, and salamanders. Amphibians usually have four limbs, eyelids, ears, and a voice-producing larynx. Adult amphibians usually have small lungs. Reptiles: Amniotic Egg The reptiles include the dinosaurs, now extinct, turtles, alligators, snakes, and lizards. Reptiles are adapted for life on land. Fertilization is internal and the female lays leathery, flexible, shelled eggs. Feathered Reptiles Birds lay a hard-shelled amniotic egg. They have scales on their legs and feathers. Diversity of Birds The majority of birds are able to fly. Some are flightless. Anatomy and Physiology of Birds Nearly every anatomical feature of a bird can be related to its ability to fly. Birds are endothermic and contain a four-chambered heart. Mammals: Hair and Mammary Glands Mammals evolved from the reptiles. The chief characteristics are body hair and milkproducing mammary glands. Monotremes 4 Monotremes are mammals that have a cloaca as a common chamber for feces, excretory wastes, and sex cells. They lay hard-shelled amniotic eggs. Marsupials The young of marsupials begin their development inside the female’s body, but they are born in a very immature condition. Newborns crawl up into a pouch on their mother’s abdomen, attach to the nipples of mammary glands, and continue to develop. Placental Mammals The vast majority of living mammals are placental mammals. The extraembryonic membranes have been modified for internal development within the uterus of the female. The mammalian brain is well-developed and enlarged due to the expansion of the cerebral hemispheres. Mammals also have differentiated teeth. Primates Primates are members of the order Primates. They are adapted to an arboreal life (living in trees). Primate limbs are mobile, and the hands and feet both have five digits each. The evolutionary trend among primates is toward a larger and more complex brain. 31.4 Human Evolution All primates share one common ancestor and the other types of primates diverged from the human line of descent over time. Humans are most closely related to African apes. Evolution of Humanlike Hominins To be a hominin, a fossil must have an anatomy suitable for standing erect and walking on two feet. Australopithecines Australopithecines is the possible direct hominid ancestors for humans. There were robust and gracile forms. Evolution of Early Homo Early Homo species all have a brain size that is 600 cc or greater, their jaw and teeth resemble those of humans, and tool use is in evidence. Homo habilis and Homo rudolfensis H. habilis used tools. The speech centers of the brain are enlarged. Homo ergaster and Homo erectus Compared to H. habilis, H. ergaster had a larger brain and a flatter face. These were the first to use fire, and both types used more advanced tools. Homo floresiensis It appears that this type coexisted with modern Homo sapiens. Evolution of Modern Humans The multiregional continuity hypothesis proposes that modern humans arose from archaic humans in essentially the same manner but in different locations. The out-of-Africa hypothesis proposes that modern humans evolved only in Africa and then migrated to Europe and Asia. Neandertals The Neandertal brain was slightly larger than that of Homo sapiens. They had massive brow ridges and wide, flat noses. Evidence suggests that Neandertals were culturally advanced. Cro-Magnon Cro-Magnons are the oldest fossils to be designated Homo sapiens. They had a thoroughly modern appearance. They were the first to have language. 5