1. 27-1 Flatworms

2. Acoelomate Animal lacking a coelom, or body cavity

3. Coelom Fluid-filled body cavity lined with mesoderm

4. Pharynx Muscular tube at the end of the gastrovascular cavity, or throat, that connects the mouth with the rest of the digestive tract and serves as a passageway for air and food.

5. Flame Cell Specialized cell that filters and removes excess water from the body of a flatworm.

6. Ganglion Group of nerve cells

7. Eyespot Group of cells that can detect changes in the amount of light in the environment.

8. Hermaphrodite Individual that has both male and female reproductive organs

9. Fission Form of asexual reproduction in which an organism splits into two, and each half grows new parts to become a complete organism.

10. Scolex Head of an adult tapeworm; can contain suckers or hooks.

11. Proglottid One of the segments that make up most of a tapeworm’s body.

12. testis Male reproductive organ that produces sperm.

13. Key Concept Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization

14. Key Concept Turbellarians are free-living flatworms. Most live in marine or fresh water.

15. Key concept Flukes are parasitic flatworms. Most flukes infect the internal organs of their host.

16. Key Concept Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts.