toheroa Amphidesma ventricosum, the most famous of the edible bivalves of New Zealand. It is a large clam (record length over 30 cm/1', usual size half of that) with relatively thin and brittle shells, yellowish or grey. It is a relatively agile bivalve, capable of moving sideways through the sand and a strong burrower; its long twin siphons allow it to live about 25 cm (10") below the surface of the sand.
The toheroa occurs only in certain localities on the west coast of the North Island and in Foveaux Strait. Although it has, in the past, been locally very abundant, toheroa populations have been severely declining for the last 30 years and harvesting is now subject to strict controls; the variable ‘close season’ sometimes extends right through the year. Toheroa continues to defy the efforts of scientists to cultivate it and establish this unique bivalve as a form of aquaculture.