Polynesian tree snail (Samoana burchi)

Description

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Polynesian tree snail fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Polynesian tree snail description

Once thought to have become extinct in the 1980s, Samoana burchiwas rediscovered in 2007 living on a single island in the South Pacific ⁽³⁾. This elusive snail has a pale brown body and a conical shell that appears to have patches of brown, grey and cream. Interestingly, the shell itself may be unpigmented, with the coloured mantle underneath creating its mottled appearance ⁽⁴⁾.

Size

Shell height: 11 - 30 mm ⁽²⁾

Polynesian tree snail biology

Little has been documented on the basic biology of Samoana burchi, but snails of the Partulidae family usually live in trees, feed on a wide range of partially decayed and living plant matter, and live for a relatively long time ⁽²⁾. From birth, growth is rapid and the snail reaches adult size relatively quickly. The formation of a flared tip at the shell opening marks maturity ⁽²⁾.

Partulid snails such as Samoana burchi are hermaphroditic and may either breed with others or self-fertilise. The reproduction of these species is relatively slow and usually one to ten eggs are produced, although the young are born live as the eggshell is reabsorbed by the parent before birth ⁽²⁾.

Polynesian tree snail range

Samoana burchi is endemic to Tahiti, the largest of the Society Islands, in French Polynesia in the South Pacific. However, no live individuals were found during searches of the island in the 1980s, 1990s, or during an intensive survey from 2003 to 2005 ⁽³⁾.

Samoana burchi was therefore believed to be extinct until, in 2006, high altitude tree snail populations on Mt. Marau, previously thought to be Samoana attenuata,were proved to be Samoana burchi by molecular analysis ⁽³⁾.

Polynesian tree snail habitat

Having once inhabited moist lowland and high montane areas, Samoana burchiis now only known to survive in Tahitian montane forest areas above 1,000 metres ^{(3) (5)}. Like other tree snails of its genus, it is likely that it spends most of its time in trees, only moving within a range of a few metres throughout its entire life ⁽²⁾.

Polynesian tree snail status

Classified as Critically Endangered (CR) on the IUCN Red List ⁽¹⁾.

Polynesian tree snail threats

Samoana burchiis a member of the Partulidae, a family that was once abundant across French Polynesia and attracted the interest of evolutionary biologists due to its high diversity ⁽²⁾. Tragically this is no longer the case as many of the species within this family are now extinct, and those that remain, including Samoana burchi, face a similar fate ⁽⁶⁾.

In 1977, a carnivorous land snail, Euglandia rosea,was introduced to Tahiti in an attempt to control the giant African snail Achatina fulica, a species considered a pest to crops and gardens ⁽¹⁾(3) ⁽⁴⁾. Without adequate scientific field trials prior to its release, this carnivorous snail began preying upon all land snails endemic to French Polynesia, and fewer than 20 of the 70-plus Partulidae species are known to have survived ^{(2) (3) (6)}.

As well as predation by Euglandia rosea, other threats to Samoana burchi include habitat loss due to the installation of communications systems, forest clearance to improve tourist views ⁽¹⁾, and the replacement of native plants with non-native species that are unsuitable for partulid snails ⁽⁴⁾. In addition, Samoana burchi is under threat of extinction because of the low genetic diversity remaining in the few individuals that make up the surviving populations ⁽³⁾.

Polynesian tree snail conservation

Captive breeding colonies of Samoana species have so far been unsuccessful. The current conservation of Samoana burchi is therefore limited to its management and protection in the wild ⁽¹⁾.

In 2009, studies conducted on Tahiti and Moorea, a neighbouring island, showed that three partulid snails, Partula taeniata, Partula hyalina and Partula clara, have been able to survive long-term exposure to predation ⁽⁵⁾. A study into the possible genetic or ecological factors that have enabled the survival of these species could prove useful when developing a feasible long-term conservation plan for other partulid snails in the region ⁽⁵⁾. Such a plan could offer new hope for Samoana burchi populations that have been devastated by introduced predators.

Find out more

More information on partulid snails and their conservation:

• Zoological Society of London - International Partula Conservation Programme:
  http://www.zsl.org/conservation/regions/americas/snail-wars-in-the-pacific,45,AR.html

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Glossary

Carnivorous

Feeding on flesh.

Endemic

A species or taxonomic group that is only found in one particular country or geographic area.

Genetic diversity (Genetic variation)

The variety of genes within a particular species, population or breed causing differences in morphology, physiology and behaviour.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Hermaphroditic

Possessing both male and female sex organs.

Mantle

In molluscs, a fold of skin that encloses a space known as the mantle cavity, which contains the gills. The mantle is responsible for the secretion of the shell.

Montane

Of mountains, or growing in mountains.

Self-fertilisation

Fusion of male and female sex cells (gametes) from the same individual. In contrast, in cross-fertilisation, two different individuals are involved.

References

1. IUCN Red List (2010)  
   http://www.iucnredlist.org/
2. Cowie, R.H. (1992) Evolution and extinction of Partulidae, endemic Pacific Island land snails. Philosophical Transactions: Biological Sciences, 335(1274):  167-191.
3. Coote, T. (2007) Partulids on Tahiti: differential persistence of a minority of endemic taxa among relict populations. American Malacological Bulletin, 22: 83-87.
4. Goodacre, S.L. and Wade, C.M. (2001) Molecular evolutionary relationships between partulid land snails of the Pacific.Proceedings of the Royal Society B- Biological Sciences, 268(1462): 1-7.
5. Lee, T., Burch, J.B., Coote, T., Pearce-Kelly, P., Hickman, C., Meyer, J.Y. and Foighil, D.O.(2009) Moorean tree snail survival revisited: a multi-island genealogical perspective. BMC Evolutionary Biology, 9: 204.
6. Lee, T., Burch, J.B., Jung, Y., Coote, T., Pearce-Kelly, P. and Ó Foighil, D. (2007) Tahitian tree snail mitochondrial clades survived recent mass-extirpation. Current Biology, 17(13): 502-503.