This photograph shows three medium-sized shallow-water snails, along with three tiny deep-sea snails (at upper left).

This photograph shows a tiny deep-sea snail compared with a US quarter.

This giant deep-sea isopod is an example of an animal that has evolved to a much larger size in deeper water. These isopods are distant relatives of the tiny "pill bugs" found in many gardens. They are also related to small shallow-water isopods that live in tide pools.
(Original NOAA image here).

This drawing illustrates how large animals, such as elephants, may become smaller after being isolated on islands, whereas relatively small animals, such as shrews, sometimes evolve into larger species.

This drawing illustrates how the "island rule" applies to deep-sea snails. Large shallow-water snails tend to evolve into smaller species in deep water, while tiny snails often grow larger.