|Apical view of a shell of Powelliphanta hochstetteri hochstetteri|
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.
Genus PARYPHANTA Albers, 1850.
Shell generally, similar to Paryphanta Albers, but with the last whorl pulled in closer to the preceding whorl, and with a colour pattern of concentric or radially arranged bands, usually of alternating and contrasting colours. More important is the paucity of lime compared with conchin in the shell.
Egg always with cuticle, pale buff when laid.
Distribution: North Island of New Zealand, in and south of the Ruahine Range (possibly once as far north as East Cape) and South Island.
Type: Helix hochstetteri Pfeiffer, Mal. Bl., viii, 146, 1862 (see PI. 6, Figs. 5–8).
Powelliphanta will include all New Zealand species previously included in Paryphanta except the type of that genus, P. busbyi (Gray, 1840) which is confined to the North Auckland Peninsula.
(For list, see Powell, 1938, pp. 140, 141.)
The sub-genus is named in recognition of the great service rendered to the study of the family by Mr A. W. B. Powell.
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[which?], thought to be extinct, was rediscovered alive on the West Coast; it had last been documented on the basis of shell fragments in 1934.
These snails live mostly in tiny pockets of moist native bush and large native forests.
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.
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.
An unspecified species of Powelliphanta recently appeared on a New Zealand 40-cent postage stamp.
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. 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. 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. The introduced hedgehog are also a threat to Powelliphanta species.
The subspecies Powelliphanta gilliesi brunnea and Powelliphanta traversi otakia are the most threatened.
Species within the genus Powelliphanta include:
This article incorporates public domain text from New Zealand from the O'Connor reference.
- O'Connor A. C. (June) 1945. Notes on the Eggs of New Zealand Paryphantidae, With Description of a New Subgenus. Transactions of the Royal Society of New Zealand, volume 5, 1945-46, pages 54-57.
- Department of Conservation YouTube video showing effects of possum predation on Powelliphanta: http://www.youtube.com/watch?v=Rm1Rjod-VU0&feature=player_embedded
- Department of Conservation website: http://www.doc.govt.nz/about-doc/news/media-releases/2009/kahurangi-national-park-anatoki-pest-control-reduces-pests-and-benefits-native-species/
- Department of Conservation website: http://www.doc.govt.nz/about-doc/news/media-releases/2010/giant-snails-the-winners/
- "Hedgehogs pose prickly problem for native fauna". Landcare Research media release. 17 September 2003. Retrieved 6 December 2011.
- 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.
- 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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