In other species, a process of incomplete metamorphosis occurs in which the young somewhat resemble the adults and go through a series of stages separated by molts (shedding of the skin) until they reach the final adult form. For these animals, the young and the adult have different diets and sometimes habitats. Other animals, such as some insects and amphibians, undergo complete metamorphosis in which individuals enter one or more larval stages. In many animals, such as mammals, the young resemble the adult. During development, animal cells specialize and form tissues, determining their future morphology and physiology. Many of the events in development are shared in groups of related animal species, and these events are one of the main ways scientists classify high-level groups of animals. The body plan refers to the shape of an animal.Īfter fertilization of the egg and sperm, a developmental sequence ensues as cells divide and differentiate. After fertilization, the offspring pass through a series of developmental stages that establish a determined body plan, unlike plants, for example, in which the exact shape of the body is indeterminate. Most animals reproduce sexually, that is they engage in the process of meiosis to produce haploid cells from diploid ones. Animals may be carnivores, herbivores, omnivores, or parasites. This form of obtaining energy distinguishes them from autotrophic organisms, such as most plants, which make their own nutrients through photosynthesis and from fungi that digest their food externally.Īlthough some animals look so simple, like a sponge, others are very complex, like an elephant, and they all share the characteristics described above. All animals are heterotrophic, ingesting living or dead organic matter. Animals require a source of food to grow and develop. Most animals are motile, at least during certain life stages. Most animals undergo sexual reproduction, while many also have mechanisms of asexual reproduction. Some exceptions exist: For example, in bees, wasps, and ants, the male is haploid because it develops from an unfertilized egg. Most animals have diploid body ( somatic) cells and a small number of haploid reproductive ( gamete) cells produced through meiosis. Epithelial tissue covers the internal and external surfaces of organs inside the animal body and the external surface of the body of the organism. Connective tissue is comprised of cells separated by extracellular material made of organic and inorganic materials, such as the protein and mineral deposits of bone. Examples of connective tissues include blood and bone. Animals also have specialized connective tissues that provide many functions, including transport and structural support. Muscle tissue contracts to cause all types of body movement from locomotion of the organism to movements within the body itself. Nervous tissue contains neurons, or nerve cells, which transmit nerve impulses. There are four main types of animal tissues: nervous, muscle, connective, and epithelial. A tissue is a collection of similar cells that had a common embryonic origin. All animals are eukaryotic, multicellular organisms, and almost all animals have specialized tissues. Invertebrates include a huge diversity of animals, millions of species in about 32 phyla, which we can just begin to touch on here.Įven though members of the animal kingdom are incredibly diverse, animals share common features that distinguish them from organisms in other kingdoms. Although in general we are most familiar with vertebrate animals, the vast majority of animal species, about 95 percent, are invertebrates. The kingdom of animals is informally divided into invertebrate animals, those without a cranium, and vertebrate animals, those with a cranium. Describe the derived features that distinguish primates from other animals.Name and describe the distinguishing features of the three main groups of mammals.Describe the derived characteristics in birds that facilitate flight.Explain the main characteristics of amphibians, reptiles, and birds.Describe the difference between jawless and jawed fishes.Describe the structure and distinguishing characteristics of the animal phyla.Describe the organizational features of cnidarians.Describe the organizational features of the simplest animals, the sponges.Compare and contrast the embryonic development of protostomes and deuterostomes.Explain the processes of animal reproduction and embryonic development.List the features that distinguish the animal kingdom from other kingdoms.By the end of this section, you will be able to:
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