Powelliphanta

Powelliphanta is a genus of large, air-breathing land snails, pulmonate gastropods in the family Rhytididae, found only in New Zealand. They are carnivorous, eating invertebrates, mostly native earthworms. Often restricted to very small areas of moist forest, they are prey to introduced mammalian predators, and many species are threatened or endangered. Powelliphanta was originally described by A. C. O'Connor in 1945 as a subgenus of the kauri snails, Paryphanta. They were named 'in recognition of the great service rendered to the study of the family by Mr A. W. B. Powell', and from their similarity to Paryphanta. In 1977 Climo raised Powelliphanta to genus rank, retaining just two species in Paryphanta. There are at least 21 species and 51 subspecies within the genus. The relationship between the species is complex, and it has been suggested that the group Powelliphanta gilliesi-traversi-hochstetteri-rossiana-lignaria-superba forms a ring species. In November 2003 a subspecies, thought to be extinct, was rediscovered alive on the West Coast; it had last been documented on the basis of shell fragments in 1934. Powelliphanta are endemic to New Zealand, ranging in the North Island from Lake Waikaremoana to the Kapiti Coast, and in the South Island from the Marlborough Sounds to Fiordland and Southland. Their greatest diversity is in the mountains of northwest Nelson and north Westland. Some species have an extremely restricted distribution, such as Powelliphanta gilliesi brunnea, which is only found in a 1 ha remnant of coastal forest. These snails live mostly in moist native forest. Some live in lowland forest, such as P. traversi traversi, which is nationally endangered and has its own 10 ha reserve of kahikatea forest and raupo swamp near Levin. Other species live in upland forest, or even under tussock grasses above the treeline. Several species only inhabit forests on limestone soils; they require calcium to build their shells and eggs, and this is obtained from eating invertebrates (including other snails) which have taken up calcium from the limestone environment. Powelliphanta require a moist environment because, unlike other land snails, they cannot seal off their shells with a protective mucous membrane. The largest species, Powelliphanta superba prouseorum, has a shell up to 9 cm across and can weigh 90 g. The striking delicately patterned shells of Powelliphanta come in an array of shades, from brown or red to yellow or black. The structure of these shells is very delicate, with a very thin layer of calcium carbonate, covered by a thicker chitinous outer layer. These snails need moist surroundings, otherwise the outer layer (periostracum) dries, shrinks and cracks; this sometimes happens in museum shells of this genus which have been stored dry. Powelliphanta are carnivorous, eating mostly earthworms or slugs. They are nocturnal, and during the day live buried under leaf litter and logs. Powelliphanta uses a rudimentary radula to devour their prey: a tongue-like belt of teeth, which scrapes chunks of flesh into the oesophagus. Far from being swallowed whole, prey are subjected to prolonged radulation.