The « Darwin's Piddock » is a spectacular South American pholadid with a very peculiar shape, ranging from southern Brazil to Argentina. A rock-burrowing bivalve, it repeatedly rotates its shells using a set of specially adapted muscles to mechanically grind a tubular burrow in soft rocks, which it then reside within for the rest of its life. It is a filter-feeder inhabiting very shallow to shallow waters down to about 15m deep, during feeding it extends its siphons out of the burrow but rest of the body remains protected by the rock. A rather rare species, perhaps owing to the fact that it is difficult to locate, and even more difficult to extract intact from its rocky burrow. Typical shell length around 30mm., very large specimens may exceed 40mm. The genus Nettastomella was erected by Carpenter in 1865 to house this eccentric species, but it is now deemed to be an unnecessary replacement name for genus Netastoma, its current genus.

Found at San Jorge Gulf, Caleta Olvia, Santa Cruz, Argentina