Which of the following organisms is an ectoparasite?

An ectoparasite is a type of parasite that lives on the outside of the host's body, feeding on blood or other bodily fluids. Among the options provided, the flea is the only organism that fits this description and is an ectoparasite. Fleas are tiny insects that live on the skin of animals, such as dogs and cats, and feed on their blood. They can cause itching, irritation, and even transmit diseases to their hosts. In contrast, the liver fluke and roundworm are internal parasites that live inside the body of their host, while the cattle egret is a bird that does not feed on the bodily fluids of other animals and is not a parasite. Therefore, the answer to the question is Flea.