Lord Howe flax snail

The Lord Howe flax snail or the Lord Howe placostylus, scientific name Placostylus bivaricosus, is a species of large air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Bothriembryontidae.

Lord Howe flax snail

Critically Endangered  (IUCN 2.3)[1][1]
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Gastropoda
(unranked):
clade Heterobranchia clade Euthyneura
clade Panpulmonata
clade Eupulmonata
clade Stylommatophora
informal group Sigmurethra
Superfamily:
Orthalicoidea
Family:
Bothriembryontidae
Subfamily:
Placostylinae
Genus:
Placostylus
Species:
P. bivaricosus
Binomial name
Placostylus bivaricosus
(Gaskoin, 1855)
P. bivaricosus is endemic to Lord Howe Island

This large snail is found only on Lord Howe Island off the east coast of Australia. Its conservation status has declined from common to endangered since rats were accidentally introduced to this World Heritage island in 1918.

Subspecies

Subspecies of Placostylus bivaricosus include:

  • Placostylus bivaricosus bivaricosus (Gaskoin, 1855)[2]
  • Placostylus bivaricosus etheridgei (Hedley, 1891)[2] - extinct[3]
  • Placostylus bivaricosus cuniculinsulae (Cox, 1872)[2]
  • Placostylus bivaricosus solidus (Brazier in Etheridge, 1889)[4][2]

Description

The genus Placostylus is a group of large ground dwelling gastropods with a disjunct distribution in the South west Pacific from the Solomon Islands, Fiji, and New Caledonia, to Lord Howe Island and the northern extremity of New Zealand. The Lord Howe flax snail has a brown, pointed shell up to 7 cm long and 2 cm in diameter.

Conservation

Species decline

Historical accounts and fossil evidence indicate that the Lord Howe Island flax snail was formerly widespread and abundant on the island. The decline was first noted in the 1940s and the species is now listed as critically endangered.

The black rat is considered to be the major predator of this species and likely to be a significant threat to its survival. European blackbirds and song thrushes (self-introduced around 1950) are also thought to be predators of the snail.

Habitat clearing and modification and habitat disturbance, possibly herbicides and pesticides also add to the species decline.

Recovery

In 2001, a recovery plan was completed to protect and recover the Lord Howe Island flax snail in the wild. Actions include habitat and population surveys, community awareness raising and a captive-breeding program.

The Lord Howe Island Board, responsible for implementation of the recovery plan, has since constructed a rodent and bird proof enclosure for the project and the first generation of captive bred Lord Howe Island land snails has hatched.

Over a period of two years, schoolchildren will closely monitor the captive snail population and their eggs, and will then measure growth rates and survival rates of the juvenile snails.

Rodent control or eradication on the island is crucial for the long-term survival of this snail in the wild.

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References
  1. Ponder, W.F. (1996). "Placostylus bivaricosus". IUCN Red List of Threatened Species. 1996: e.T17447A7077965. doi:10.2305/IUCN.UK.1996.RLTS.T17447A7077965.en.
  2. Ponder W. F., Colgan D. J., Gleeson D. M. & Sherley G. H. (2003). "Relationships of Placostylus from Lord Howe Island: an investigation using the mitochondrial cytochrome c oxidase 1 gene". Molluscan Research 23(2): 159-178. doi:10.1071/MR03001, PDF.
  3. Ponder W. F. (1996). "Placostylus bivaricosus ssp. etheridgei". In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.3. www.iucnredlist.org. Downloaded on 29 September 2010.
  4. Etheridge, R. (31 December 1889). "The general zoology of Lord Howe Island; containing also an account of the collections made by the Australian Museum Collecting Party, Aug.–Sept., 1887" (PDF). Australian Museum Memoir. 2 (1): 1–42. doi:10.3853/j.0067-1967.2.1889.479. Retrieved 23 January 2019.
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