Archive for the ‘mollusk shells’ tag

Importance of Saliva   no comments

Posted at 5:12 pm in Teeth

In far from all cases are the teeth the best possible tools, and nature has not hesitated to substitute more perfect technical means for them. Many species of the prosobranchiate snails feed on mollusks which are rather large and enclosed in a hard shell. To make a hole in the shell with a radula would take weeks or even months, and the radula would wear out. Therefore, these snails use a specific saliva instead of teeth, which is a four-percent solution of sulphuric acid. Nor is this very strange, for if the glandular cells of man's stomach secrete hydrochloric acid, why should snails not make use of sulphuric acid?

The acid secreted by the snails is so strong that it hisses and effervesces when falling on marble. It dissolves the mollusk shells quite easily. When attacking their prey, the snails apply their saliva to the shell which loosens a small section of it. The preying snail then bores a hole with its radula, inserts its proboscis and is then able to enjoy eating the defenceless victim.

It is not always enough to crush food for it to pass easily into the gullet. This is why the 'preparatory shop' contains the large and small salivary glands for both the mechanical and chemical processing of food. Saliva performs many important functions, but the most important seems to be to wet each lump of food which otherwise would not pass into the oesophagus. Anyone who had a chance to observe the European pond tortoises was easily convinced of the importance of saliva. The pond tortoises have no salivary glands. They eat their prey in water, amply washing down each mouthful. But on land they are helpless since completely dry food sticks in their throats.

The saliva of most animals contains substances (enzymes) which are the first to act chemically on the food being taken in. Nature subsequently developed these properties, making saliva somewhat poisonous. This is necessary as numerous microorganisms, most of them harmful to the organism, may lodge in the moist membrane of the mouth and the remains of food stuck between the teeth.

Written by rickweak on January 4th, 2010

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