Here's an illustrative recipe from "Tahitian Cooking".

The turbot snails are available around here++in pet stores for something like eight bucks a pop! They might be available in a Chinese seafood market for a reasonable price. I'll check the next time I'm up that way.

The snail of the ma'oa may be extracted from the shell either by breaking the shells with a hammer or by boiling them for a few minutes if you wish to keep the shells intact. Wash the snails and remove the pocket of black matter. In the case of the pahua, a bivalve, the muscle adhering to the shell should be severed, the animal extracted from the shell, and the black matter removed. Soak in fresh water for a few hours. Mix with the taioro, then add the chopped onions and garlic plus seasoning. Serve at room temperature. [Note that there's no mention of actually cooking the stuff... S.C.]

From "Tahitian Cooking", Michel Swartvagher and Michel Folco. Le editions du pacifique, Papeete-Tahiti, 1980. Isbn 2-85700-062-6.