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.