What is unique about the body structure of ants?

The uniqueness of an ant's body structure lies in its segmentation into three distinct parts: the head, thorax, and abdomen. This segmentation is a characteristic feature of all insects, but in ants, it plays a crucial role in their physiology and behavior. The head houses critical sensory organs such as antennae and mouthparts, the thorax is responsible for locomotion with its three pairs of legs, and the abdomen contains vital organs and may also house the reproductive system. This compartmentalization allows for specialized functions and adaptability, making ants highly effective in their ecological roles.

The other options present characteristics that do not apply to the general body structure of ants, thereby reinforcing why the segmented body is the defining characteristic of their anatomical makeup. Specifically, ants have legs, their antennae are typically bent or elbowed rather than straight, and they undergo complete metamorphosis rather than incomplete, which further showcases the distinct traits of this remarkable group of insects.