Monoplacophora
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Monoplacophora is a class of Mollusks thought to be extinct until 1952, when a living animal was dredged up from deep marine sediments. They have a flat, rounded shell and resemble chitons (Class Polyplacophora) or more precisely, limpets (Class Gastropoda). Their body segments exhibit a primitive serial repetition with similar organs in several segments. This form resembles the antomy of worms of Phylum Annelida, suggesting a link between mollusks and annelids.
Neopilina galatheae was the first known living specimen. It is classified in order Tryblidiia and family Neopilinidae. Previous specimens dated from the Paleozoic. These mollusks are about 0.5 to 3.0 cm in length. There are about a dozen known species.