They also concluded that banana slugs are able to endure longer periods of intense weather as compared to the Arion ater slug. They attribute this to the large surface area to volume ratio which causes less evaporative stress. The banana slug is a mollusk, which came from the sea. Their stages of evolution can be seen in other various species of land and sea mollusks. The tremendous adaptation variation in slug traits such as size and color, make their fossils challenging to classify.
Divergent evolution is evident in the variation between internal and external shells.
Other's, like the banana slug, conceal remnants of their shell within their small bodies. Land snails have limited themselves to conditions of high moisture, the need for protection from light and heat, but have moved away from their dependency on calcium rich soils due to the shedding of their external shell. In retrospect, they also lost their prized protective barrier, allowing predators easy access to a terrestrial treat. In return, banana slugs are able to live in a wider range of environments. The Cambrian Period of the geological time scale is the first division of the Paleozoic era in which the ancestral wormlike mollusca existed.