Biology 2 · ELI Explains Biology, Part 2 (book)
Animal Evolution and Diversity
On this page 2 sections
The college version
Animal Evolution and Diversity
IN THIS PART
Chapter 17 · What Makes an Animal an Animal?
Chapter 18 · Reading Animal Body Plans
Chapter 19 · Sponges
Chapter 20 · Cnidarians and Ctenophores
Chapter 21 · Flatworms, Nemerteans, and Rotifers
Chapter 22 · Mollusks
Chapter 23 · Annelids and Lophophorate Animals
Chapter 24 · Nematodes
Chapter 25 · Arthropods
Chapter 26 · Echinoderms and Hemichordates
Chapter 27 · Chordate Origins and Invertebrate Chordates
Chapter 28 · Vertebrate Foundations and Fishes
Chapter 29 · Amphibians
Chapter 30 · Reptile-Line Amniotes
Chapter 31 · Birds
Chapter 32 · Mammals
Chapter 33 · Comparative Vertebrate Anatomy and Physiology
Chapter 34 · Animal Reproduction and Life Cycles
Part II explores the extraordinary diversity of animals — from sponges to mammals. You will learn to read animal body plans like architectural blueprints, trace the major evolutionary innovations that produced today’s animal diversity, and understand how structure supports function in organisms ranging from microscopic rotifers to blue whales. By the end of Part II, you should be able to examine any animal and identify its body plan, infer its mode of life, and place it within the larger evolutionary story.
Major Learning Themes
• Animal body plans reflect evolutionary history and ecological function.
• Symmetry, tissues, body cavities, segmentation, and developmental patterns define major animal groups.
• Evolution modifies existing structures — every new adaptation is built on what came before.
• Animals are not a ladder of progress; each living group is adapted to its own way of life.
• Chordates and vertebrates represent one branch of animal diversity, not its endpoint.
ELI-10 Preview: Animals come in an astonishing variety of shapes and sizes, but underneath that variety are a few basic architectural plans — like different types of buildings constructed from the same materials. Learning to recognize these body plans — Does it have symmetry? How many tissue layers? A body cavity? A through-gut? Segments? — is the key to understanding animal diversity without drowning in names.
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