Monoplacophorans (Class Monoplacophora)

Monoplacophorans have a single, flat, rounded bilateral shell that is often thin and fragile.

Monoplacophorans were thought to be extinct, but on May 6, 1952, ten living specimens were discovered. While trawling off the Pacific coast of Costa Rica, the Danish deep-sea "Galathea" expedition hauled these specimens to the ocean surface from a depth of 3590 meters. They were given the name Neopolina galathea and their discovery has been described as "the most dramatic one in the history of malacology." When Neopilina was discovered it became the only living representative of Monoplacophora and for this reason it is often referred to as a "living fossil."

Since the initial discovery of Neopilina in 1952, at least 30 species have been described. During a recent cruise in the north-eastern Tasman Sea, two new species were obtained in a single station on the West Norfolk Ridge (at 785-800 m), and a third on the Reinga Ridge (at 394-400 m), while a fourth was collected on the Chatham Rise (at 880-973 m).

This brings the total known from the New Zealand region to six species, the others being from the Three Kings Rise (at 1216-1385 m) and off Puysegur Point (at 896-1038 m). All have been described by Dr. Bruce Marshall. Although the group occurs in all major ocean basins, from the tropics to the Antarctic, they have gone undetected until relatively recently because of their rarity and deep water habitat. They are typically associated with ferromanganense deposits.