I grew up with a deep appreciation for the sea. Our family holidays always featured scrambling over the rocky shoreline hunting for interesting critters. As you can imagine, I always took the most commonplace species for granted, yet it appeared the humble limpet, that most boring of animals, holds a seriously surprising secret.
Limpets, for me at least, were the unlovable gastropod that were almost impossible to remove from the rocks unless you sneak up on them and catch them unawares. Once they detect your presence, they cling on pretty hard.
Most limpets (true limpets belong to the order Patellogastropoda, though some references more accurately describe this as a ‘clade’) are smallish animals, with conical, highly robust shells a few inches across. Moist species return to their home patch between their spells of grazing and create a small indentation, known as a ‘scar’, in their home rock, into which their shell adapts perfectly as the rock and shell slowly wear away to create a very predator-resistant seal.
The species I am most familiar with is Patella vulgata, a common species from my region, though there are species found on rocky shores worldwide. When I kept fish, I would often take a few of the animals as treats – as you can imagine, their muscular foot makes for good eating.
In some countries, such as Portugal, limpets are considered a delicacy and I must admit to enjoying them myself, but I digress.
Being grazing herbivores, limpets use a tongue-like structure known as a Radula to scrape away algae from rocky surfaces, or algal tissue from macroalgae, while a few outlying species target seagrass.
The radula of all gastropods (apart from bivalves) is quite a feat of engineering and is covered with microscopic teeth, arranged in various ways that reflect the species’ lifestyle. A quick web search will reveal an awful lot of complicated information about teeth direction, layers and so on. What amazes me though is the substance limpets use.
According to a paper from two years ago, (which I can’t believe I missed), the teeth of limpets are made from the strongest known biological material.
Material scientists have long known that spider silk is seriously impressive, with a tensile strength that exceeds that of steel and is comparable with some of the most up-to-date carbon fibers. Limpet teeth go further! This is achieved by the remarkable nano structure of limpet teeth which employs goethite nanofibers. Goethite is a mineral containing iron which when combined with the chitin (a very tough protein) in the limpet’s teeth gives these often-overlooked creatures a remarkable claim to fame.
The teeth of limpets exploit distinctive composite nanostructures consisting of high volume fractions of reinforcing goethite nanofibres within a softer protein phase to provide mechanical integrity when rasping over rock surfaces during feeding. The tensile strength of discrete volumes of limpet tooth material measured using in situ atomic force microscopy was found to range from 3.0 to 6.5 GPa and was independent of sample size.