Which of the following structures is absent in worms?

Worms, particularly terrestrial ones like earthworms, do not possess eyes and ears as found in many other animals. Instead, they have light-sensitive cells that allow them to detect changes in light, which helps them navigate their environment. Their sensory perception is primarily based on touch and chemical signals rather than vision or sound. This adaptation suits their burrowing lifestyle, where they mainly interact with soil rather than needing formal eyes or ears for communication or navigation.

In contrast, other structures mentioned, such as skin and muscles, are essential for the worm’s movement and bodily functions. Worms have a layer of skin that acts as a protective barrier and contains muscles that help facilitate their locomotion through the soil. The presence of nerves and blood vessels is crucial for their physiological processes, enabling them to respond to stimuli and transport nutrients. Lastly, while worms do not have lungs or a heart as mammals do, they use their skin for gas exchange and have a simplified circulatory system that pumps blood through vessels, indicating that having lungs and a heart is indeed absent in worms.