Shells are often battered and broken by the time they are washed up on the beach for us to find. Have you noticed, though, that on many intact shells there is a perfectly round hole, almost as if someone took a drill to it and tossed it back on the beach?
Many times, a snail drilled that hole in the shell. Snails have a tongue-like structure, called a radula, covered in tiny chitinous teeth. Some snails use the radula to bore right through the shells of other mollusks.
Predatory snails hold their prey with their foot while the radula goes to work drilling through the shell. A gland near the radula secretes chemicals that weaken the prey’s calcareous shell, making it easier to drill. Once the hole is drilled, and the mollusk killed, the snail can pry open the shell and feast upon the meaty insides.
Although some shells might seem fragile, drilling through them with a radula can really do a number on the tiny teeth of a snail. Thankfully, the teeth on the radula are continually replaced as they are worn down so the snail can continue to drill.
One of these little snails is causing a pretty big stir. The oyster drill, as its name suggests, preys upon oysters, causing millions of dollars in damage.
The radula is a structure unique to the Phylum Mollusca, and is found among all mollusks except for bivalves. Depending on the species, the radula is adapted for different types of feeding. Not all of them are as exciting as drilling through other shells. Some merely scrape algae from rocks or other hard surfaces.
Next time, we will explore the great molluskan harpooners, the Cone Shells.
Bet you never thought snails could be so vicious!