Do flatworms have a closed circulatory system?

Hint: Circulatory system is a system through which blood and lymph circulate throughout the body. It consists of the heart, blood, blood vessels, lymph, lymphatic vessels, lymphoid organs, and lymph nodes. The circulation system helps our body to circulate oxygenated blood, nutrients, and hormones to different parts of the body and helps in the removal of waste material produced like carbon dioxide.

Complete answer:
Flatworms don’t have a closed circulatory system, in fact, they don’t have any circulation system.
Platyhelminthes are also known as flatworms because of their appearance. They have a dorso-ventrally flattened body thus giving a flat image. Their bodies are much simpler in comparison with the human body so they don’t need any circulatory system for circulation.
Flatworms breathe through their moist body surface (skin) and diffusion of oxygen takes place directly. By this diffusion process, each cell can meet its oxygen requirements thus there is no need for the circulatory system to circulate oxygen and nutrients.

Note:
Circulatory system is of two types
OPEN TYPE- In this type of circulatory system blood is pumped out of the heart and cells are directly bathed in it.
CLOSED TYPE- In this type of circulatory system blood is circulated throughout the body with the help of blood vessels.
There are three different types of blood vessels-
Arteries- They carry oxygenated blood from the heart to different body parts.
Veins- They carry deoxygenated blood from body parts to the heart.
Capillaries- They are thin blood vessels that connect arteries and veins and carry oxygenated and deoxygenated blood.