Which of the following organisms has gills located internally?

The correct answer is the dragonfly, as this organism possesses internal gills that are located within its body. In the aquatic nymph stage, dragonflies have gills that help them extract oxygen from water, facilitating their underwater breathing and survival. These gills are not externally visible, distinguishing them from the gills of other organisms that may exhibit external structures for respiration.

In contrast, mayflies and stoneflies typically have their gills located externally on their bodies, often on the abdomen or thorax, which are readily visible when observing these insects. Snails, on the other hand, do have gill structures for respiration, but they are also adapted for life outside of water and generally possess a lung-like structure in terrestrial species. Thus, the internal gill structure is a key characteristic that identifies the dragonfly among the options provided.