27-1 Flatworms

Acoelomate

• Animal lacking a coelom, or body cavity

Coelom

• Fluid-filled body cavity lined with mesoderm

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.

Flame Cell

• Specialized cell that filters and removes excess water from the body of a flatworm.

Ganglion

• Group of nerve cells

Eyespot

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

Hermaphrodite

• Individual that has both male and female reproductive organs

Fission

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

Scolex

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

Proglottid

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

testis

• Male reproductive organ that produces sperm.

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

Key Concept

• Turbellarians are free-living flatworms. Most live in marine or fresh water.

Key concept

• Flukes are parasitic flatworms. Most flukes infect the internal organs of their host.

Key Concept

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