KEY CONCEPT More than 95 percent of all animal species are invertebrates.

1. KEY CONCEPTMore than 95 percent of all animal species are invertebrates.

2. Each animal phylum has a unique body plan. • Vertebrates have an internal segmented backbone. • Invertebrates do not have a backbone. • Invertebrates encompass most animal groups.

3. head tail fruit fly genes human HOX-B genes tail head • Hox genes tell embryonic cells which body part to become. • Differences in body plans result from differences in the expression of Hox genes. • Mutations in Hox genes led to the vast diversity of animal species.

4. Three criteria are used to categorize animals. body plan symmetry mouth gastrovascular cavity mesoglea brain muscle hearts blood vessels oral arms tentacles mouth digestive track segment nerve cord Animals are grouped using a variety of criteria. • tissue layers • developmental patterns

5. bilateral symmetry: body divides equally along one plane • There are two types of body plan symmetry. Animals with bilateral symmetry can be divided equally along only one plane, which splits an animal into mirror-image sides.

6. There are two types of body plan symmetry. • bilateral symmetry: body divides equally along one plane • radial symmetry: body arranged in circle around a central axis Animals with radial symmetry have body parts arranged in a circle around a central axis.

7. Bilateral animals have three distinct layers of tissue; radial animals have only two. • both animal types have ectoderm and endoderm • bilateral animals have mesoderm • Animals are divided into two major groups, the protostomes and the deuterostomes. • Protostomes form mouth-first, and anus second. • Deuterostomes first form the anus and then the mouth.

8. Protostomes and deuterostomes are the two major radiations on the animal phylogenetic tree. Annelida Porifera Cnidaria Platyhelminthes Echinodermata Mollusca Arthropoda Nematoda Chordata Segmented worms sea stars, sea urchins sponges clams, snails, octopuses flatworms lancelets, vertebrates crustaceans, insects, spiders roundworms jellyfish, coral, anemones RADIAL DUETEROSTOMES PROTOSTOMES NO TISSUES A comparison of structure and genetics reveals the evolutionary history of animals.

9. The current organization of the animal kingdom shows some unexpected relationships. • Technological advancementshelp to clarify evolutionaryrelationships.