Snails

Snails are invertebrate terrestrial or aquatic animals that, in general, belong to the molluscan class Gastropoda that can often retract into their shells.  


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A garden snail crawling along a wet footpath. image: R.Conan-Davies

Snails are  most often considered as land or garden snails, and known scientifically as pulmonate ( Pulmo , meaning lungs or air breathing) gastropod molluscs.

Image of a garden snail

A typical garden snail. image: Jürgen Schoner wikipedia


The common name "snail" is applied to most of the members of the molluscan class Gastropoda that have a coiled shell that is large enough for the animal to retract completely into. 

When the word "snail" is used in this most general sense, it includes not just land snails but also thousands of species of sea snails and freshwater snails. 

Things like snails but may not be

Occasionally a few other molluscs that are not actually gastropods, such as the Monoplacophora, which superficially resemble small limpets, may also informally be referred to as "snails".

No shells or very small shells

Snail-like animals that naturally lack a shell, or have only an internal shell, are mostly called slugs, and land snails that have only a very small shell (that they cannot retract into) are often called semi-slugs.


Anatomy of a snail

Diagram of a land air breathing snail (Helix aspersa). image: A12 wikipedia



How snails move

Land snails move by gliding along on their muscular foot, which is lubricated with mucus and covered with epithelial cilia. 

 This motion is powered by succeeding waves of muscular contractions that move down the ventral of the foot. 

This muscular action is clearly visible when a snail is crawling on the glass of a window or aquarium. 

The contractions of the snail muscles are visible in this video. video: OceanSplash/youtube


 Snails move at a proverbially low speed (1 mm/s is a typical speed for adult Helix lucorum). 

What is that snail slime?

Snails secrete mucus externally to keep their soft bodies from drying out. They also secrete mucus from the foot to aid in locomotion by reducing friction, and to help reduce the risk of mechanical injury from sharp objects, meaning they can crawl over a sharp edge like a straight razor and not be injured.



Source: adapted from
 Snail. (2015, August 1). In Wikipedia, The Free Encyclopedia. Retrieved 04:25, August 6, 2015, from https://en.wikipedia.org/w/index.php?title=Snail&oldid=674081081

Land snail. (2015, June 15). In Wikipedia, The Free Encyclopedia. Retrieved 04:32, August 6, 2015, from https://en.wikipedia.org/w/index.php?title=Land_snail&oldid=667105250