Monoplacophora is a class or, more likely, polyphyletic group of shelle mollusks (the name "Monoplacophora" means 'bearing one plate'). Previously, these organisms were known only from the fossil record, and thought to have become extinct in mid-Devonian times, until in April 1952 a living specimen was collected from deep marine sediments in the Middle America Trench off the Pacific coast of Costa Rica. In 1957 it was described and named Neopilina galatheae by its discoverer, Danish biologist Dr. Henning M. Lemche (1904-1977) . So far, more than two dozen living species of Monoplacophora have been discovered; the first to be photographed live was Vema hyalina, at a depth of 400 m off Catalina Island, California, in 1977. All the present species live deep down in the abyssal depths of ocean trenches. An attempt at a common name, gastroverm, has proved unsuccessful.