A parasite that is flat and segmented, living in the small and large intestine is called ____.

The correct answer is tapeworm, which is a type of flatworm that is characterized by its flat, segmented body. Tapeworms inhabit the intestines of their host, often the small and large intestines of various animals, including dogs and cats. The segments, called proglottids, are part of the tapeworm's structure and can break off and pass out in the host's feces, allowing for the spread of the parasite.

In understanding why this option is accurate, it is important to distinguish it from the other types of worms. Roundworms, for example, are cylindrical, not flat, and have a different body structure and habitat. Flatworm could be somewhat misleading since it broadly refers to a category that includes tapeworms, but it does not specify that we are talking about the segmented type that is typically found in the intestines. Threadworms are also not segmented and have a different life cycle and bodily structure.

Thus, identifying the specific characteristics of tapeworms makes this choice the most precise and accurate in the context of the question regarding the type of parasite that is flat, segmented, and lives in the intestines.