“What would I give if I could live out of these waters?”

As evolution transitioned water-dwelling snails to a life on land, these creatures developed several adaptations to survive in a drier habitat.  Terrestrial snails like Zonitoides limatulus have several features that allow them to enjoy a life above the sea. (The little mermaid would be envious of this.  But unlike Ariel, Z. limatulus has no intention of returning to underwater living.)  First of all, the tough calcium carbonate-based shell of a land snail helps to protect it against dryness and predation (Nordseick, 2011). Most of the snail's internal organs are contained within its shell, with only necessary organs located externally, such as the foot, mouth, and breathing and sensory organs (Hickman et al., 2009). A snail's mucus-like slime is also a very helpful defense against evaporation, and also helps with locomotion.  An interesting feature of snail slime is that it is hygroscopic, meaning that it attracts water molecules to it rather than releasing moisture (Nordseick, 2011). A snail’s behavior is also an aid to its survival; if its surroundings are too dry, it will seek to find shelter somewhere more suitable. (Nordseick, 2011).  The muscular foot of a snail aids with this, allowing for transportation on dry land(Nordseick, 2011).

“What would I pay to spend a day warm on the sand?"

Terrestrial snails no longer have a use for a comb gill, or ctenidium (Nordseick, 2011) Instead, they have adapted a mantle, complete with lungs,Photo courtesy of for the ability to obtain oxygen from the air(Nordseick, 2011)This, however, poses the problem of losing internal moisture through exhalation.  Evolution has helped them to adapt to this with the development of a pneumostome, which is a respiratory pore (Hickman et al., 2009)Land snails have the ability to open and close this hole with a ring of muscle, and can control the flow of air into the mantle cavity.  The lining of the mantle is composed of a thicker tissue to help avoid drying out (Nordseick, 2011). 

I would try to explain to you the evolutionary science behind the mermaid Ariel’s marine to terrestrial transition, but that’s a website for a different day.

It is interesting, though, that the scallop shells that Ariel dons on her bosom are also of the phylum Mollusca, belonging to the class Bivalvia.  Her friend Sebastian, also pictured below, is a crustacean of the phylum Arthropoda (Hickman et al., 2009).

                            Photo courtesy of

“Out of the sea, wish I could be part of that world!”

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 Lyrics courtesy of Alan Menken and Howard Ashman.