Chapter 44

Summary		Questions		Media Resources
44.1 Animals are multicellular heterotrophs without cell walls.
• Animals are heterotrophic, multicellular, and usually have the ability to move. Almost all animals reproduce sexually. Animal cells lack rigid cell walls and digest their food internally. • The kingdom Animalia is divided into two subkingdoms: Parazoa, which includes only the asymmetrical phylum Porifera, and Eumetazoa, characterized by body symmetry.		1. What are the characteristics that distinguish animals from other living organisms? 2. What are the two subkingdoms of animals? How do they differ in terms of symmetry and body organization?		•Symmetry in Nature •Posterior to Anterior •Sagittal Plane •Frontal to Coronal Plane •Transverse/Cross-sectional Planes •Characteristics of Invertebrates •Activity: Invertebrates •Animal Kingdom Phylogeny •Bilaterally Symmetrical Animals
44.2 The simplest animals are not bilaterally symmetrical.
• The sponges (phylum Porifera) are characterized by specialized, flagellated cells called choanocytes. They do not possess tissues or organs, and most species lack symmetry in their body organization. • Cnidarians (phylum Cnidaria) are predominantly marine animals with unique stinging cells called cnidocytes, each of which contains a specialized harpoonlike apparatus, or nematocyst.		3. From what kind of ancestor did sponges probably evolve? 4. What are the specialized cells used by a sponge to capture food? 5. What are the two ways sponges reproduce? What do larval sponges look like? 6. What is a planula?		•Sponges •Radial Phyla • Cnidarian Body Plan
44.3 Acoelomates are solid worms that lack a body cavity.
• Acoelomates lack an internal cavity, except for the digestive system, and are the simplest animals that have organs. • The most prominent phylum of acoelomates, Platyhelminthes, includes the free-living flatworms and the parasitic flukes and tapeworms. • Ribbon worms (phylum Nemertea) are similar to free-living flatworms, but have a complete digestive system and a circulatory system in which the blood flows in vessels.		7. What body plan do members of the phylum Platyhelminthes possess? Are these animals parasitic or free-living? How do they move from place to place? 8. How are tapeworms different from flukes? How do tapeworms reproduce?		•Bilateral Acoelomates •Parasitic Flatworms
44.4 Pseudocoelomates have a simple body cavity.
• Pseudocoelomates, exemplified by the nematodes (phylum Nematoda), have a body cavity that develops between the mesoderm and the endoderm. • Rotifers (phylum Rotifera), or wheel animals, are very small freshwater pseudocoelomates.		9. Why are nematodes structurally unique in the animal world? 10. How do rotifers capture food?		•Pseudocoelomates
44.5 The coming revolution in animal taxonomy will likely alter traditional phylogenies.
• Molecular data are suggesting animal phylogenies that are in considerable disagreement with traditional phylogenies.		11.  With what group are myzostomids most closely allied?

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