O'ahu tree snail

Oʻahu tree snail
Achatinella bulimoides
Achatinella lila
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
(unranked): clade Heterobranchia

clade Euthyneura
clade Panpulmonata
clade Eupulmonata
clade Stylommatophora
clade Orthurethra

Superfamily: Achatinelloidea
Family: Achatinellidae
Subfamily: Achatinellinae
Genus: Achatinella
Swainson, 1828
Diversity
41 species,[1]

9 extant species remained in 2014[2]

Oʻahu tree snails, genus Achatinella, are a large genus of colorful, tropical, tree-living, air-breathing, land snails, arboreal pulmonate gastropod mollusks in the family Achatinellidae.

This genus of tree snails live in Hawaii, and all are endangered species. They were once abundant. They were mentioned in Hawaiian folklore and songs, and their shells were used in lei and other ornaments.

Many of these arboreal snails are sinistral or left-handed in their spiral shell coiling, whereas most gastropod shells are dextral. (See the section on chirality in the article gastropod shell.)

Distribution

There are 41 species[1] of Oʻahu tree snail endemic to Hawaiian island of O`ahu. All are endangered, there being only about hundred individuals of each species left.

Conservation status

All 41 species are listed under United States federal legislation as endangered. The IUCN lists a number of these species as extinction and the remainder as critically endangered. In many cases the introduced and highly predatory snail Euglandina rosea has been involved in the extinctions and declines of the native tree snails.[3]

O'ahu tree snail shells collected ca. 1933 at an elevation of 1500 feet on Waialae Ridge in Waialae Country Club, Honolulu, Hawaii.

Shell description

Oʻahu tree snails are diverse in patterns, colors, and shapes, but all average about 0.75 in (1.9 cm) in length. Most have smooth glossy, and oblong or ovate shells which show a variety of colors, including yellow, orange, red, brown, green, gray, black, and white.

There are three recognized subgenera within the genus Achatinella.[4] Subgenera are distinguished according to shells characteristics only.

Genus Achatinella Swainson, 1828: The dextral or sinistral shell is imperforate or minutely perforate, oblong, ovate or globose-conic; smooth or longitudinally corrugated, with only weak traces of spiral sculpture. Shell color is in spiral bands or streaks in the direction of the growth lines. The lip is simple or thickened within and sometimes slightly expanding. The columella bears a strong callous fold. Type species of the genus Achatinella is Achatinella apexfulva (Dixon).[4]

Subgenus Bulimella Pfeiffer, 1854: Shell shape is oblong-conic or ovate. The spire is obtuse, rounded or convexly-conic near the apex. The outer lip is thickened by a strong callous rib within the aperture (except in Achatinella abbreviata and Achatinella lila). Type species of the subgenus Bulimella is Achatinella byronii Newcomb.[4]

Subgenus Achatinellastrum Pfeiffer, 1854: The shell is imperforate, ovate-conic or oblong-conic and smooth. The embryonic whorls are not flattened. The outer lip is thin or only slightly thickened within the apex but not expanded. These are the most generally distributed of the Achatinella species and show a prolific area of intergrading color patterns. Type species of the subgenus Achatinellastrum is Achatinella stewartii (Green, 1827).[4]

Ecology

Habitat

These snails live in trees. Currently they are only found in mountainous dry to moist forests and shrublands above 1,300 ft (400 m).

Feeding

These tree snails are nocturnal, and feed by grazing fungus which grows on the surface of native plant leaves.

Although these tree snails are occasionally found on introduced plants, it is unknown whether or not the fungus which grows on these plants can provide long-term support for healthy breeding populations of these snails.

In captivity Achatinella feed on fungus growing on leaves of Metrosideros polymorpha. They also feed on cornstarch, which can be spread in terraria with water and on cultures of sooty mold grown on laboratory agar. In captivity, cuttlebone is used as a source for calcium.[4]

Life cycle

Adult snails are hermaphroditic (having both male and female reproductive organs) and can live for many years. These are live bearing snails (give birth to live snails instead of laying eggs).

Predation and other threats

Because growth rate and fertility are very low, these snails are especially vulnerable to loss of individuals through human collection, through predation, or because of other disturbances.

The most serious threats to the survival of Oʻahu tree snails are predation by the introduced carnivorous snail Euglandina rosea, predation by rats (Rattus exulans, Rattus norvegicus, Rattus rattus),[1] and loss of habitat due to the spread of non-native vegetation into higher elevation forests.

Jackson's chameleon Trioceros jacksonii, that was introduced to Hawaii in early 1970s, is a serious threat to Achatinella, because it directly prey on them and on other snails too.[1][2] Other predators of Achatinella include the land planarian Platydemus manokwari.[1]

Predators of Achatinella:

Species

There are 40 species in the genus Achatinella:[4]

subgenus Achatinella
subgenus Bulimella
subgenus Achatinellastrum

References

This article incorporates public domain text (a public domain work of the United States Government) from reference.[4] [5] [6] [7]

  1. 1 2 3 4 5 Holland B. S., Montgomery S. L. & Costello V. (2010). "A reptilian smoking gun: first record of invasive Jackson’s chameleon (Chamaeleo jacksonii) predation on native Hawaiian species". Biodiversity and Conservation 19(5): 1437-1441. doi:10.1007/s10531-009-9773-5.
  2. 1 2 Chiaverano L. M. & Holland B. S. (2014). "Impact of an invasive predatory lizard on the endangered Hawaiian tree snail Achatinella mustelina: a threat assessment". Endangered Species Research 24: 115-123, doi:10.3354/esr00589.
  3. ↑ Régnier, Benoît and Bouchet (2009). Not Knowing, Not Recording, Not Listing: Numerous Unnoticed Mollusk Extinctions. Conservation Biology 23(5): 1214–1221
  4. 1 2 3 4 5 6 7 U.S. Fish and Wildlife Service. (1992) Endangered Species Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella. U.S. Fish and Wildlife Service, Portland, Oregon, 64 pp. + 64 pp. of appendices + 5 figures. PDF
  5. ↑ Holland, B.S. & M.G. Hadfield. 2007. Molecular systematics of the endangered O‘ahu tree snail Achatinella mustelina (Mighels 1845): Synonymization of subspecies and estimation of gene flow between chiral morphs. Pacific Science, 61(1): 53-66.
  6. ↑ Holland, B.S. & M.G. Hadfield. 2004. Origin and diversification of the endemic Hawaiian tree snails (Achatinellinae: Achatinellidae) based on molecular evidence. Molecular Phylogenetics and Evolution. 32(2): 588-600.
  7. ↑ Holland, B.S. & M.G. Hadfield. 2002. Islands within an island: phylogeography and conservation genetics of the endangered Hawaiian tree snail Achatinella mustelina. Molecular Ecology 11: 365-375.

Further reading

External links

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