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Mollusks have teeth too

By Staff | Dec 11, 2009

One of the remarkable features in mollusks is their teeth, or radula (plural radulae). The radula consists of a thin, flexible ribbon, onto which a number of teeth are attached and aligned in transversal rows. During their food-gathering activities, mollusks are able to bend the radula around a central bolster and move it back-an-forth like an electric belt sander, releasing food particles for swallowing and digestion.

Generally speaking, the number and shape of radular teeth are contingent on the type of feeding performed by that particular mollusk. Plant-eaters usually have many teeth per row, with the teeth in any given row being similar to each other; the opposite is usually true for predators and scavengers, which tend to have fewer teeth per row, with the teeth in any given row being very different from each other.

It sounds simple, but there is huge variety of teeth shapes, number, and arrangements in mollusks. With exception of bivalves, which lost their radula in the course of their evolution, all classes of mollusks have a radula, with gastropods exhibiting the larger degree of radular diversification of all Mollusca.

Plant-eating land snails have radulae that resemble cheese graters, with a large number of very small teeth per row. Some murexes and rock snails can drill slowly through the shells of their prey, in some cases with help from chemical substances. Cone snails have highly modified, harpoon-like teeth that are hollow and capable of delivering potent toxin “cocktails” to immobilize and kill their prey.

Many volutes (including the junonia) have radulae with only one tooth per row (“unisserial” radulae). A couple of volute species have radular teeth that resemble the hands with very long fingernails of Edward Scissorhands, the main character played by Johnny Depp in Tim Burton 1990’s tragic-comic movie of the same name. Unlike Edward, however, who suffered from having overdeveloped, dangerous fingernails and could not find use for them, our volutes rely on the long cusps on their radular teeth to slash their prey, most likely the soft tissues of sea anemones and their relatives.

Last but not least, chitons have iron oxides in their radular teeth. These dark metallic minerals not only provide strength to the chitons’ teeth, but, are in some cases magnetized, acting as compasses to help orient the animals back to their home spots on the rocks after a foray for food.