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You won’t find a radula on the human body, but it is a common anatomical feature of animal species in the phylum mollusca . Biologists describe it as a scratchy dental tape that replaces the mammalian tongue. Oysters, clams, and other bivalves are the only molluscs that do not have this organ.
Structure and function of mollusks
Mollusks are a very diverse phylum and some are almost microscopic. The colossal squid is the largest mollusk, weighing over 500 kilos and can be bigger than a school bus.
The main distinguishing feature of these animals is a hard outer shell that covers the upper part of the body and encloses the internal organs. For their part, the heads of the mollusks are another world and can have multiple variations. Some heads, for example, may be diversified with mobile appendages used to distinguish their environment or to catch some type of food. Mollusks usually have a muscular foot that is used for walking; however, in many species this foot has evolved and been modified to be used for other purposes.
Two unique features of mollusks are the mantle and the radula. Here is a summary of each one.
Between the shell and the body is a layer of tissue called the mantle. The mantle produces calcium carbonate, which is responsible for forming the shell. In turn, this shell forms a cavity between the mantle and the body called the mantle cavity. The mantle cavity draws in water that it feeds with a method called filtration.
At the front of the mouth, on the head, is the radula. This organ, which is made up of teeth made of a polysaccharide (chitin), allows the mollusk to feed. Herbivorous molluscs use the radula to scrape food such as algae from rocks. Other mollusks, such as predators, use the radula to pierce the shells of their prey.
Characteristics and uses of the radula
As we already mentioned, the radula is an anatomical structure found in mollusks and used for feeding. However, that is only one of its features; here we mention others:
Hardness
Although the radula serves a function similar to that of the tongue in many other animals, there are some fundamental differences. Unlike the soft, fleshy organ in the human mouth, the radula is made of a hard material called chitin.
According to Tulane University’s Department of Biology, at the molecular level chitin is made up of a nitrogen group attached to a cellulose polymer. This is the same material that we find in the hard exoskeletons of various creatures, as well as in the cells of fungal species.
Resembling a mouth full of teeth
Radulas are often compared to chainsaws, as they are covered in hundreds of tiny teeth arranged in rows. In fact, this organ, which is smaller, can house up to 25,000 teeth, in the case of herbivorous mollusks.
Inside the radula there is a cartilage that fulfills a structural objective, allowing to improve the friction between the surfaces. The length of the radula varies according to the species. Some measure less than a millimeter, while those of the largest species are much longer.
Form meets function
The radula of each species of mollusk varies, since it has adapted to the specific feeding needs of each one. Some examples are:
- Some plant-eating species, such as chitons, can collect small algae that are attached to rocks in the water thanks to their radula, which is flat and also wrapped in tiny teeth.
- The radulas of carnivorous moon snails are designed to pierce the hard shells of clams and other prey.
- Other mollusks use their radula to break down their food into smaller, easier-to-digest pieces, including squid and larger mollusks.
A curious fact about the radulas is that when they wear out, they can be replaced by other tissue that, in fact, is constantly growing and forming inside the body of the mollusk.
It could be a lethal injection
Although most mollusks use their radula for grating, chewing, or boring, some species have developed more twisted applications for their particular dental organ.
Cone snails ( conidae ) are carnivorous snails. Your radula is equipped with only one tooth at a time and stores spare teeth in a retention bag so that the single tooth can be replaced immediately after each use. The radula device works like a barbed harpoon that injects venom into the snail’s prey. This venom is a paralyzing toxin made from the amino acids in the snail’s own body.
