The developing embryo absorbs calcium from the calcified egg shells to form the first whorl called a protoconch (Tompa, 1976). Take notice of the spirals on the shell in the photo below. These are the whorls. Interestingly, nature has provided a way to further the calcium uptake by the newly born snails. The juvenile snails, after having hatched from their egg, will consume what is left of their calcified egg shell to maximize their calcium uptake (Tompa, 1976).

The shell is composed primarily of calcium carbonate, CaCO3 (Tompa, 1976). The adult Mesodon zaletus shell consists of 5.5 to 6 whorls (Dourson, 2006). The shell is lined with transverse striations that lie perpendicular to the whorls (Dourson, 2006).

Photo courtesy of Bill Frank     

 Shells composed of calcium carbonate 

 At maturity, the shell diameter can reach sizes of up to 24-31 mm (Emberton, 1993).

The shell is imperforate (solid) and contains a parietal tooth on the inner wall (Dourson, 2006). Newly hatched snails have shells that do not exhibit the parietal tooth as evident in the adult (Emberton, 1993). Also, the shell is dextral, meaning that it has a right-handed whorl (Franzen, 1944).

Mesodon zaletus
moves with a foot, otherwise known as a muscular base
(Coppolino, 2009). The foot contracts in a wave-like motion in the direction in which the snail is moving (Coppolino, 2009). However, some limitations would arise in that the foot would possibly get stuck or friction could be too great for the snail to move a decent distance without some sort of lubrication. Fortunately, they have developed a means to overcome this obstacle. Glands within their muscular foot secrete mucous to reduce friction and aid in their movement (Coppolino, 2009). Think about it in this way; it is easy run and slide along a layer of ice in the winter with rubber soled shoes, but in the summer time the coefficient of friction is too great and rubber shoes on pavement sticks all too well, limiting your ability to slide across the surface. The mucosal lining increases their mobility along the ground, reducing the coefficient of friction much in the same way ice does to rubber soled shoes, allowing the snail to move more easily across the surface.


 A graphical review of the juvenile and adult: