Oahu 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 or left-handed in their spiral shell coiling, whereas most gastropod shells are dextral. (See the section on chirality in the article gastropod shell.)
There are 40 species of O?ahu tree snail endemic to Hawaiian island of O`ahu. All are engendered, there being only about hundred individuals of each species left.
All 40 species are listed under United States federal legislation as endangered. The IUCN lists a number of these species as extinct and the remainder as critically endangered.
O?ahu 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.
 Subnenera 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).
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.
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).
These snails live in trees. Currently they are only found in mountainous dry to moist forests and shrublands above 1,300 ft (400 m).
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.
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 O?ahu tree snails are predation by the introduced carnivorous snail Euglandina rosea, predation by rats, and loss of habitat due to the spread of non-native vegetation into higher elevation forests.
There are 40 species in the genus Achatinella:
- Achatinella apexfulva (Dixon, 1789)
- Achatinella cestus Newcomb, 1853
- Achatinella concavospira Pfeiffer, 1859
- Achatinella decora (F?russac, 1821) - extinct
- Achatinella leucorraphe (Gulick, 1873)
- Achatinell a lorata F?russac, 1824
- Achatinella mustelina Mighels, 1845
- Achatinella swiftii Newcomb, 1853
- Achatinella turgida Newcomb, 1853
- Achatinella valida Pfeiffer, 1855 - extinct
- Achatinella vittata Reeve, 1850
- Achatinella abbreviata Reeve, 1850 - extinct
- Achatinella bulimoides Swainson, 1828
- Achatinella byronii (Wood, 1828)
- Achatinella decipiens Newcomb, 1854
- Achatinella fuscobasis (E. A. Smith, 1873)
- Achatinella lila Pilsbry, 1914
- Achatinella pulcherrima Swainson, 1828
- Achatinella pupukanioe Pilsbry & Cooke, 1914
- Achatinella sowerbyana Pfeiffer, 1855
- Achatinella taeniolata Pfeiffer, 1846
- Achatinella viridans Mighels, 1845
- Achatinella elegans Newcomb, 1853 - extinct
- Achatinella bellula E. A. Smith, 1873
- Achatinella buddii Newcomb, 1853 - extinct
- Achatinella casta Newcomb, 1853 - extinct
- Achatinella caesia Gulick, 1858 - extinct
- Achatinella curta Newcomb, 1853
- Achatinella dimorpha Gulick, 1858 - extinct
- Achatinella fulgens Newcomb, 1853
- Achatinella juddii Baldwin, 1895 - extinct
- Achatinella juncea Gulick, 1856 - extinct
- Achatinella lehuiensis E. A. Smith, 1873 - extinct
- Achatinella livida Swainson, 1828 - extinct
- Achatinella papyracea Gulick, 1856 - extinct
- Achatinella phaeozona Gulick, 1856
- Achatinella spaldingi Pilsbry & Cooke, 1914 - extinct
- Achatinella stewartii (Green, 1827)
- Achatinella thaanumi Pilsbry & Cooke, 1914 - extinct
- Achatinella vulpina (F?russac, 1824)