New Zealand has a rich and varied shellfish fauna, although most of the species lack the brilliance of colouring and the polish of those from the tropical Pacific.
This country is but a remnant of a once continental land mass. Today over 1,200 miles of deep ocean separate it from Australia, the nearest existing continental mass. Conditions of more or less isolation from other lands have pertained during most of the Tertiary, that is, for a period of 40 million years or more. Fluctuations in climate have undoubtedly resulted not only in many extinctions but also in adaptations to changing conditions, without the stabilising influence, to any great extent, of the advent of new stock from outside areas. One looks in vain for the colourful cones and highly enamelled cowries of the tropical Pacific, yet both occurred here in the Oligocene and Miocene when the climate was considerably warmer than that of today. Nevertheless, despite these several adverse factors, New Zealand has developed a shellfish fauna almost unique in respect to the very high percentage of truly endemic species. Including land and freshwater forms, our shellfish fauna now numbers over 2,200 different species and subspecies belonging to 646 recognised genera.