Achatinella is a tropical genus of colorful land snails in the monotypic Achatinellidae subfamily Achatinellinae. Species are arboreal pulmonate gastropod mollusks with some species called Oʻahu tree snails or kāhuli in the Hawaiian language. Achatinella species are all endemic to the island of Oahu in Hawaii, and all remaining extant species are endangered. They were once abundant and were mentioned extensively in Hawaiian folklore and songs, and their shells were used in lei and other ornaments. Many of the species are sinistral or left-handed chirality in their spiral shell coiling, whereas most gastropod shells are dextral, with a right handed spiral. Distribution There were 41 species of Achatinella endemic to the Hawaiian island of Oʻahu, though only 13 species survive. Some species have less than 50 remaining individuals, and others have +300; many species fall in between. Conservation status All 13 species are listed under United States federal legislation as endangered. The IUCN lists a number of Achatinella species as extinct and the remainder as critically endangered. The main cause of decline has been attributed to over collection. In addition, invasive species such as rats, Jackson's chameleons, and the highly predatory snail Euglandina rosea have been involved in the extinctions and declines of the native tree snails. Shell description Achatinella species shells are diverse in patterns, colors, and shapes, but all average about 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. 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). 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