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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.