Types of Flatworms

As their name suggests, flatworms are a member of the worm species, are flat and have no skeleton. Very simple creatures, they utilize tiny hair-like features called cilia to move, have two small brains made only of nerves and have only one digestive tract opening, meaning they take in food and excrete waste through the same opening. Flatworms reproduce by splitting themselves in two, with both halves creating a new flatworm. There are more than 20,000 species of flatworms, which can be separated into three different types.

Planaria

• Also known as Dugesia, planaria live in freshwater. They are scavengers and often feed on protists (unicellular, water-dwelling organisms that cannot be classified a plant, animal or fungus). Like all flatworms they are hermaphrodites, meaning they contain both male and female reproductive entities and can reproduce on their own. Planaria can also regenerate parts if necessary.

Tapeworms

• Perhaps the most recognizable flatworm, tapeworms are parasitic, most notoriously living in animal and human digestive tracts. Tapeworms are made of many body segments called proglottids. Each segment contains reproductive organs, allowing the tapeworm to grow very long; some tapeworms can grow up to 40 feet in length. They attach themselves to the host's intestines through suckers on their heads, allowing them to survive by stealing nutrients.

Flukes

• Flukes have a more complex life cycle than other flatworms. Their life cycle usually consists of more than one host. For example, schistosoma are flukes that live in the blood stream. They spend part of their life in snails, and then infect humans when they enter the water. Their larvae then make a home in the human's blood vessels. To complete the cycle, these flukes are passed through human feces back into the water where another snail is then infected.

Roundworms

• Although not technically a type of flatworm, roundworms are usually associated with flatworms because of their many similarities. Like tapeworms and flukes, roundworms are parasitic and are commonly found in humans and dogs. However, unlike flatworms, roundworms have a complete digestive tract, meaning that they take in food and excrete waste from two separate openings.