Powelliphanta

Powelliphanta
Apical view of a shell of Powelliphanta hochstetteri hochstetteri
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
(unranked):	clade Heterobranchia clade Euthyneura clade Panpulmonata clade Eupulmonata clade Stylommatophora informal group Sigmurethra
Superfamily:	Rhytidoidea
Family:	Rhytididae
Genus:	Powelliphanta O'Connor, 1945[1]
Species
See text.

Powelliphanta, common name the amber snails, is a genus of large, air-breathing, carnivorous land snails, terrestrial pulmonate gastropod molluscs in the family Rhytididae. As a group their survival status is endangered.

Taxonomy

The generic name was given in honour of New Zealand's malacologist Arthur William Baden Powell, and derived from the genus's similarity to Paryphanta.^[1]

Powelliphanta was originally described by A. C. O'Connor in 1945 as a subgenus of Paryphanta.^[1]

There are 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.

Distribution

These large snails are endemic to New Zealand, in small areas of the North and South Islands, with the greatest diversity of species in the mountains of northwest Nelson in the South Island.

Habitat

These snails live mostly in tiny pockets of moist native bush and large native forests.

Shell description

These gastropods are large, with shells up to 9 cm across (Powelliphanta superba prouseorum).

Their striking delicately patterned shells 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 happens often in museum shells of this genus which are stored dry; when they dry too much, the shell shatters explosively into fairly small pieces.

Life habits

Species in the genus Powelliphanta are carnivorous and eat mostly earthworms or slugs. They are nocturnal. They need moist surroundings and thus they live buried under leaf mould and logs.

They can live for 20 years or more and are slow to mature, reaching sexual maturity around 5 years of age. They are hermaphrodites, having both male and female characteristics. They lay 5 to 10 large eggs a year.

Powelliphanta uses a rudimentary radula to devour its prey. The radula is like a belt of teeth, which scrapes chunks of flesh into the oesophagus. Far from being ingested whole, its prey are subjected to prolonged radulation.

Fossil record

Their origin goes back 200 million years to the continent Gondwana. Through their isolation in New Zealand, they have evolved a unique set of characteristics^{[citation needed]}.

Cultural relevance

An unspecified species of Powelliphanta recently appeared on a New Zealand 40-cent postage stamp.

Conservation status

The IUCN Red List states for Powelliphanta marchantii a lower risk, near threatened. But most of these snails are under serious threat or even in danger of extinction. They have no defence against introduced predators, such as common brushtail possums, (Trichosurus vulpecula), and rats. Possums have been shown to eat up to 60 snails in one night.^[2] Controlling predatory mammals is now critical to the survival of Powelliphanta, and many recovery plans are being undertaken by the Department of Conservation. After aerial application of 1080 poison, Powelliphanta "Anatoki Range" numbers increased threefold at sites in Kahurangi National Park, with large numbers of juveniles present. Prior to the 1080, there were 54 snails found on 500sq grid. One year after the 1080 drop, 147 snails were found on the same plot.^[3] Between 1994 and 2010, a series of three aerial 1080 operations over 3430ha of the Ruahine Forest Park has resulted in significant increases in Powelliphanta marchanti.^[4] The introduced hedgehog are also a threat to Powelliphanta species.^[5]

The subspecies Powelliphanta gilliesi brunnea and Powelliphanta traversi otakia are the most threatened.

Species

Species within the genus Powelliphanta include:

References

This article incorporates public domain text from New Zealand from the O'Connor reference.^[1]

• Department of Conservation information.
• K. Walker (2003). "Recovery plans for Powelliphanta land snails 2003–2013 (Threatened Species Recovery Plan 49)" (PDF). Department of Conservation, Wellington, New Zealand. Retrieved 2007-09-05. 

Further reading

• Department of Conservation. (2000) "Recovery plans for Powelliphanta land snails 2002–2012". Department of Conservation, Wellington, New Zealand.
• Walker K. J. (2003) "Recovery plans for Powelliphanta land snails 2003–2013". Threatened Species Recovery Plan 49. Wellington, New Zealand Department of Conservation. x +208 p. + 64 pl. pages 1-12, 13-140, 141-196, 197-208.
• Meads M. J., Walker K. J. & Elliot G. P. (1984) "Status, conservation, and management of the land snails of the genus Powelliphanta (Mollusca: Pulmonata)". New Zealand Journal of Zoology 11: 277–306.

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