Mollusks contain a variety of organisms including a few different classes such as Bivalvia, Cephalopoda, and Gastropoda (Gillis, 2012). Gastropoda, being the class of Millerelix gracilis, includes snails, whelks, abalone, conchs, slugs, and nudibranchs (Gillis, 2012).
Noticing that many of these organisms are marine/ fresh water species, it is important to note that the land snail at one point evolved from full water submersion to a high and dry lifestyle on land (The Living World of Molluscs, 2012). Therefore, some adaptations that were made include the loss or decrement of gills, acquisition of water retaining abilities, more complex sensory organs, and the ability to move (The Living World of Molluscs, 2012).
A major adaptation previously mentioned on this site is called torsion. Torsion is a process in development where the anus of the animal’s body is twisted from the back of the animal to the front, resulting in the anus being above the head region (Hickman et. al., 2012). This internal arrangement is important because without it, waste products would have passed over the gills (Hickman et. al., 2012). This concept is referred to as fouling (Hickman et. al., 2012).
There is an interesting hypothesis about how torsion became a developmental staple in gastropods (Chia and Pennington, 1985). It is, that torsion was initially a form of defense in early gastropod larval stages (Chia and Pennington, 1985). At some point in evolution, a mutation then occurred which sealed this activity as an actual developmental step (Chia and Pennington, 1985).

Millerelix  shell (Image by Dan  Johnson)

Returning to the loss of the gill, it is thought to be partially due to coiling (Hickman et. al., 2012). The evolution of the shell changed from being bilaterally symmetrical to being a slanting, upward spiral (Hickman et. al. 2012). In this process, the weight transfer from the shell, due to the tilted whorl, put more pressure on one side of the body and its organs (Hickman et. al., 2012). Over time, these organs lost function and presence in the body (Hickman et. al., 2012). Consequently, the mantle became the air-breathing organ (Hickman et., al 2012).  
By using the two pairs of tentacles, snails can sense and see their environment (The Living World of Molluscs, 2012). They have a nervous system consisting of nerve cords and nervous tissue with ganglia which assist in sensory and nervous functions (Gillis, 2012).
To remain moist, snails have adapted the ability to produce thick mucus (Hickman et. al., 2012). This coat of mucous protects and prevents the snail from drying (Hickman et. al., 2012). Snails tend to hide in cooler, darker, more moist places when weather becomes very hot and dry (The Living World of Molluscs, 2012).

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