Planaria
Planaria are several free living (non-parasitic). They are the simplest of all flat worms, and most live in fresh or salt water, while some do live in soil. They may be black, brown, grey, or white, and the can grow to be around 1/2 an inch. They travel with a gliding motion by their cilia, but can move with a rapid crawling motion also.
Planaria also have no circulatory system or respiratory system. Oxygen and Carbon Dioxide enters and leaves it's body, by diffusing through the body wall.
Planaria also have no circulatory system or respiratory system. Oxygen and Carbon Dioxide enters and leaves it's body, by diffusing through the body wall.