A limpet the size of your palm. Not the small, pebble-like limpets that cling to the rocks in rock pools – the ones you can flick off with your finger. A limpet with a shell as wide as your hand, as thick as a coin, as strong as a stone. That was the giant tidepool limpet, and it was the rock ghost of the tidal pools. Size and strength made it special. A 10-centimetre limpet is a formidable creature. Its shell is thick and conical, designed to deflect the force of the waves. Its foot is a powerful muscle that can grip the rock with a force of hundreds of pounds. Once a giant limpet clamped down, you could not move it. You would break the rock before you broke the limpet's seal. It lived in the mid to low intertidal zone – the places where the water never fully drains, where the waves crash and the spray flies. It grazed on the film of algae that grew on the rocks, scraping the surface with its rasping radula (a tongue-like organ covered in tiny teeth). It grazed. It held on. It survived. The giant tidepool limpet was a grazer, keeping the rock surface clean of algae. Its grazing created space for other organisms – barnacles, mussels, seaweeds – to settle. It was a keystone species of the tidal pool, the one that shaped the community. Limpets reproduce by releasing eggs and sperm into the water. The larvae drift in the plankton for weeks before settling on a rock and growing into tiny limpets. That strategy works when the adults are abundant and the water is clean. It fails when the limpets are overharvested and the water is polluted. Overharvesting and introduced predators destroyed it. Māori harvested limpets for food – they were a common shellfish, easy to collect at low tide. The giant limpet, being larger, would have been a prized catch. For centuries, the harvest was sustainable. But when Europeans arrived, they harvested on an industrial scale – for food, for bait, for lime. At the same time, rats arrived. Kiore (Pacific rats) and ship rats are voracious predators of intertidal life. They patrol the rocks at low tide, flipping limpets, eating the soft bodies inside. A giant limpet, with its thick shell, might have been safe from a rat's teeth – but not from a rat's persistence. Rats could wait for the limpet to loosen its grip, then pry it off. By the 1890s, it was gone. The last specimens were probably collected by a naturalist who had no idea he was holding the final individual. He dried the shell, labelled it, put it in a drawer. And the tidal pools fell silent. The smaller limpets survived. The cellular limpet, the ribbed limpet, the serpent's shell limpet – they are still common on our rocky shores. They are smaller, faster, more adaptable. They are the survivors, the ones that kept their heads down. But the giant tidepool limpet is extinct. A few shells in a museum drawer, a few fragments in a midden, and the memory of a limpet that used to cling to the rocks like a living stone. The rock ghost has faded. The rocks are quieter than they used to be.