Neohelix alleni is in the Subclass Pulmonata of Class Gastropoda (a more detailed description of its classification can be found on the Classification page).  As a terrestrial pulmonate snail, adaptations have evolved to allow snails to migrate from water to land.  A crucial adaptation is the loss of gills and formation of an air-breathing lung from the vascularized mantle (Hickman et al., 2012).  The pneumostome is the opening to the respiratory system (Hickman et al., 2012).  

     Like all gastropods, N. alleni undergoes the process of torsion which is the 180 degree twisting of visceral mass (Gillis, 2012).  This twisting of the internal body brings the mantle cavity and the anus to an anterior position above the head (Gillis, 2012).  In the diagram below, the anus can be seen in an anterior position within the shell. 


     Torsion can cause fouling problems, since the snail excretes waste products near its mouth where it intakes food with the numerous chitinous teeth found on its radula, which is a structure designed for scraping and tearing (Gillis, 2012).  However, torsion can offer the possible advantage of allowing the snail to completely withdraw its head into its shell (Hickman et al., 2012).  

Another important adaptation that can be contributed to the successfulness of land snails is the specialization, specifically of their sensory organs, becoming localized in their heads.  This is the evolutionary process known as cephalization (Hickman et al., 2012).  Like most mollusks, Neohelix alleni have a well developed sensory and nervous system, which consists of nerve cords that connect several pairs of ganglia (Gillis, 2012).  In the diagram further above on the anatomy of a snail, eyes and cerebral ganglia can be seen in the head portion of the snail.  Unique to the subclass Pulmonata, is the location of the eyes on the tips of its posterior pair of retractable tentacles (Hickman et al., 2012).  This can also be seen on the diagram above.

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