Define Class Turbellaria - Flatworms ?

Members of these two Classes are known as the flukes. Flukes are parasitic flatworms that inhabit tropical areas like Southeast Asia and North Africa. Flukes may live part of their lives in one or more hosts such as humans, livestock, or even snails, and part of their lives in the open, usually a water body.

The parasitic lifestyle is reflected in the types of structures that these animals have, as well as in the types of structures they lack. A parasite that lives in the digestive tract of another animal doesn't necessarily need eyes or other sensory organs to help it locate prey or avoid predators. If an animal lives in a nutrient-rich environment such as the gut of its host, it may not need a mouth and digestive tract of its own; on the other hand, it may require a protective cuticle to avoid being digested. Many parasitic species have special adaptations, such as hooks and suckers to help in anchoring themselves in the gut of the host. Since flukes parasitize several intermediate hosts, of which one is usually a free-living snail, flukes must produce tremendous numbers of offspring to reproduce successfully.