Chapter Summary

Animals: Descendants of a Common Ancestor

► All members of the kingdom Animalia are believed to have a common ancestor, which was a colonial flagellated protist.

► The specialization of cells by function made possible the complex, multicellular body plan of animals.

► Animals are multicellular heterotrophs. They take in complex organic molecules, expending energy to do so.

► Morphological, developmental, and molecular data all support similar animal phylogenies.

► The two major animal lineages—protostomes and deuteros-tomes—are believed to have diverged early in animal evolution; they differ in several components of their early development. Review Figure 32.1

Body Plans Are Basic Structural Designs

► Most animals have either radial or bilateral symmetry. Radially symmetrical animals move slowly or not at all. Bilateral symmetry is strongly correlated with more rapid movement and the concentration of sense organs at the anterior end of the animal. Review Figure 32.2

► The body cavity of an animal is strongly correlated with its ability to move. On the basis of their body cavities, animals are classified as acoelomates, pseudocoelomates, or coelomates.

Review Figure 32.3

Sponges: Loosely Organized Animals

► Sponges (phylum Porifera) are simple animals that lack cell layers and true organs, but have several different cell types.

► Sponges feed by means of choanocytes, feeding cells that draw water through the sponge body and filter out food particles. Review Figure 32.4

► Sponges come in a variety of sizes and shapes that are adapted to different movement patterns of water.

Cnidarians:Two Cell Layers and Blind Guts

► Cnidarians (phylum Cnidaria) are radially symmetrical and diploblastic, but with their nematocyst-studded tentacles, they can capture prey larger and more complex than themselves. Review Figure 32.7

► Most cnidarian life cycles have a sessile polyp stage and a free-swimming, sexual, medusa stage, but some species lack one of the stages. Review Figures 32.8, 32.10, 32.11

See Web/CD Tutorial 32.1

Ctenophores: Complete Guts and Tentacles

► Ctenophores (phylum Ctenophora) are diploblastic marine carnivores with a complete gut and simple life cycles. Review Figure 32.12

The Evolution of Bilaterally Symmetrical Animals

► All bilaterally symmetrical animals probably share a common ancestor.

► Protostomes and deuterostomes are each monophyletic lineages that have been evolving separately since the Cambrian period. Their members are structurally more complex than cnidarians and ctenophores.

► Protostomes have a ventral nervous system, paired nerve cords, and larvae with compound cilia.

► Deuterostomes have a dorsal nervous system and larvae with a single cilium per cell.

► The protostomes split into two major groups: lophotro-chozoans and ecdysozoans. Review Figure 32.14

Simple Lophotrochozoans

► Flatworms (phylum Platyhelminthes) are acoelomate, lack organs for oxygen transport, have only one entrance to the gut, and move by beating their cilia. Many species are parasitic. Review Figures 32.15, 32.16

► Although they are no larger than many ciliated protists, rotifers (phylum Rotifera) have highly developed internal organs. Review Figure 32.17

Lophophorates: An Ancient Body Plan

► The lophotrochozoan lineage split into two branches, whose descendants became the modern lophophorates and the spi-ralians.

► The lophophore dominates the anatomy of many lophophor-ate animals. Review Figure 32.18

► Ectoprocts are colonial lophophorates that can move their lophophores. Review Figure 32.19

► Brachiopods, which superficially resemble bivalve mollusks, were much more abundant in the past than they are today.

Spiralians: Spiral Cleavage and Wormlike Body Plans

► The spiralian lineage gave rise to many phyla, most of whose members are wormlike.

► Ribbon worms (phylum Nemertea) have a complete digestive tract and capture prey with an eversible proboscis. Review Figure 32.21

► Annelids (phylum Annelida) are a diverse group of segmented worms that live in marine, freshwater, and terrestrial environments. Review Figures 32.22

► Mollusks (phylum Mollusca) have a body plan with three basic components: foot, mantle, and visceral mass. Review Figure 32.25

► The molluscan body plan has been modified to yield a diverse array of animals that superficially appear very different from one another.

See Web/CD Activities 32.1 and 32.3 for a concept review of this chapter

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