The Shape of Life . Platyhelminthes

Flatworms

There are more than 20,000 species of Platyhelminthes. They range from brilliantly colored creatures that swim in the ocean to parasitic flatworms that live inside the bodies of an estimated 200 million humans around the world.

Flatworms are bilaterally symmetrical with a defined head and tail region and a centralized nervous system containing a brain and nerve cords. Clusters of light-sensitive cells make up what are called eyespots. The head region of the flatworm also contains other paired sense organs, which are connected to the flatworm's simple brain.

Flatworms are hermaphroditic and capable of sexual and asexual reproduction. Their bodies have only a single opening, which serves as both a mouth and an anus.

	Learn more about Platyhelminthes in "The First Hunter"
	Website links about Platyhelminthes

The longest flatworm ever found, a tapeworm, was more than 90 feet long.


	Bilaterally symmetrical with a head and a tail
	Centralized nervous system
	Three tissue layers
	No body cavity, no circulatory system and no hard skeleton

Classification	Common Name
Artioposthia triangulata	terrestrial planarian
Triclad planarian	freshwater planarian
Diphyllobothrium latum	broad fish tapeworm
Pseudobiceros sp.	penis-fencing flatworm