1. Apply Concepts Design a “new” invertebrate
Apply Concepts Design a “new” invertebrate. Create and illustration on which you point out its body plan features. Then show its place on the cladogram of invertebrates and write a caption explaining how its features helped you decide where it belongs.

2. Ch 26 Animal Evolution and Diversity
26.1 Invertebrate Evolution and Diversity

3. Fossil evidence indicates that the first animals began evolving long before the Cambrian Explosion.

4. Origins of the Invertebrates
Roughly 3 billion years after the first prokaryotic cells evolved, all prokaryotes and eukaryotes were single-celled
Animals evolved from ancestors they shared with organisms called choanoflagellates
Single-celled eukaryotes that sometimes grow in colonies
Similar to sponges.

5. Traces of Early Animals
Oldest evidence of multicellular life comes from microscopic fossils that are roughly 600 million years old
First animals were tiny and soft-bodied, so few fossilized bodies exist.

6. Ediacaran Fauna Before the Cambrian Period
From the Ediacara Hills of Australia
Fossils 565 to about 544 million years old
Flat and lived on the bottom of shallow seas
Little evidence of cell, tissue, or organ specialization, and no organization into a front and back end.

7. Cambrian Explosion Cambrian Period began about 542 million years ago
Burgess Shale of Canada
Fossils show that over a period of 10–15 million years, animals evolved complex body plans, including specialized cells, tissues, and organs.

8. By the end of the Cambrian Period, all the basic body plans of modern phyla had been established
Later evolutionary changes, which produced the more familiar body structures of modern animals, involved variations on these basic body plans.

9. Invertebrates are the most abundant animals on Earth.

10. Sponges Phylum: Porifera Most ancient members of the kingdom Animalia
Multicellular, heterotrophic, lack cell walls, and contain a few specialized cells.

11. Cnidarians Phylum: Cnidaria
Includes jellyfishes, sea fans, sea anemones, hydras, and corals
Aquatic, soft-bodied, carnivorous, radially symmetrical animals with stinging tentacles arranged in circles around their mouths.

12. Arthropods Phylum: Arthropoda
Includes spiders, centipedes, insects, and crustaceans
Bodies divided into segments, a tough external skeleton called an exoskeleton, cephalization, and jointed appendages (legs and antennae)
Appeared in the sea about 600 million years ago.

13. Nematodes (Roundworms)
Phylum: Nematoda
Unsegmented worm with pseudocoeloms, specialized tissues and organ systems, and digestive tracts with two openings
More closely related to the arthropods than flatworms.

14. Flatworms Phylum: Platyhelminthes
Soft, unsegmented, flattened worms that have tissues and internal organ systems
Simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization
No coelms.

15. Annelids Phylum: Annelida
Includes earthworms, some marine worms, and leeches
Worms with segmented bodies and a true coelom.

16. Mollusks Phylum: Mollusca
Includes snails, slugs, clams, squids, and octopi
Soft-bodied animals that have an internal or external shell
Have true coeloms and complex organ systems
May have a trochophore
Immature free-swimming larva stage.

17. Echinoderms Phylum: Echinodermata
Includes sea stars, sea urchins, and sand dollars
Have spiny skin and an internal skeleton
Have a water vascular system that include suction- cuplike tube feet
Deuterostomes.