-30~50m, Sakai, Minabe-cho, Wakayama Prefecture, Japan, 285,1mm., 1980/iii.
The « Giant Watering Pot » is a spectacular penicillid endemic to western Pacific waters of southern Japan. Like other penicillids it also after a certain early growth stops growing the true shell and instead develops a calcareous adventitious tube, although it is unusual in switching over to growing tube exceptionally late. In most watering pot clams the true shell is only 2~5mm. in length but in this species it regularly exceeds 20mm. and is splayed open to a lesser extent. This is similar to some fossil members of the superfamily and is evidence that it is a primitive member of this extraordinary group of bivalves, hence its current placement in the monotypic genus Nipponoclava. It is an filter-feeding species living buried in soft sandy to muddy bottoms of shallow to moderate depths around -5~70m. One of the largest members of the family, it is locally uncommon but due to its restricted range it is quite rare on the international shell trade market. Typical shell length around 250mm., very large specimens may exceed even 300mm.