Hawaiia minuscula (Minute Gem)



Since Hawaiia minuscula is a terrestrial snail, it has acquired several adaptations in its body structure in order live on land and avoid water loss. For that reason, these land dwellers possess few openings to the exterior. The less openings for water to exit the body, the smaller chance for the snail dry out (Solem, 1978). Land snails have made several important adaptations in order to maintain the proper amount of moisture their body needs.

Many other subclasses of gastropods live in marine and freshwater environments and possess gills, an operculum, or perform gas exchange across the body surface (Írstan, 2006). However, the subclass pulmonata (terrestrial snails) have developed an evolved lung. The lung opens to the outside by a small opening called the pneumostome (breathing-pore), which is located on the mantle and is able to open and close(Írstan, 2006). Additionally, land snails have adapted to build replaceable sheets of (calcified) mucus on their bodies to retard water loss (Solem, 1978). Fig. 1

Another way pulmonates reduce water loss is by the process of torsion. Torsion is defined as a 180 degree twisting of the visceral mass (Solem, 1978). This twisting brings the anus to the anterior portion of the body (above the head). Therefore, water is not wasted in flushing out the cavity and snails are able to avoid predation and/or drying out (Solem, 1978). However, due to the placement of the anus near the respiratory pore, these snails tend to foul themselves with their own waste (Solem, 1978).

Terrestrial snails also produce a large internal cavity behind the pneumostome by closing off the mantle (Solem, 1978). After the mantle is sealed, the reservoir of water can be carried throughout the snail body to hydrate the snail when it needs it (Solem, 1978). This method of closing off the mantle behind the pneumostome allows land snails greater levels of freedom and mobility because they are able to stay hydrated longer (Solem, 1978).


Figure 1.  Illustration of torsion and how it develops in a snail species.


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