Flatworms are dorsoventrally flattened acoelomates with bilateral symmetry
Simplest animals to be triblastic (ecto, endo, & mesoderm)
How Many Species?
3 major classes and 25,000 species.
Structure & Function
Modern cephalization sometimes called a head
Ganglia are groups of nerve cells that form around the head region.
Flatworms have tissues, organs, and organ systems.
Flume cells however are used to regulate osmotic balance (removes excess water)
Pharynx - Food tube that serves as the only opening for the digestive system. Sucks food in.
3 Interesting Facts
1. They are estimated to live in 200 million humans around the world . 2. Tapeworms can be in sizes longer than a school bus. 3. Flatworms can stick its pharynx into their prey, like a vacuum cleaner hose, and suck out the prey's insides.
Prostheceraeus vittatus
Pseudoceros ferrugineus
Habitat
The free-living ones belong to the class Turbellaria and live in freshwater, ponds, lakes, streams and springs. Some of them are found in shores in tropical and subtropical regions.