Conservation status: The entire genus Achatinella, consisting of 41 recognized species, is endemic to the island of O'ahu. Every member of the genus is listed as endangered (USFWS 1993b); however, the USFWS considers 16 of the 41 species to be extinct (USFWS 1993c).
The HBMP Natural Diversity Database contains records of 33 Achatinella species believed to be extant, although half (16) of these are known only from historical occurrences, meaning that they haven't been recorded within the last 15 years. The 17 other Achatinella species in the HBMP database are considered critically imperilled globally and very vulnerable to extinction range wide (G1). Most of the extant Achatinella species occur only in small numbers and have restricted ranges.
Achatinella spp.
Common name: Oahu Tree Snail, Pupu Kuahiwi,
Pupu Kanioe, Kahuli Federal status: Listed endangered (USFWS 1993b)
Heritage global rank: G1 or GH (HBMP 1994b)
Description: The shells of adult Achatinella are 17 to 24 millimeters in length with 5 to 7 whorls. The oblong to ovate shells have a somewhat glossy surface. Many shells are brightly colored with spiral bands or streaks running in the direction of the growth lines. Color varieties within a species can vary from tree to tree (USFWS 1993c).
Distribution: Achatinella species once occurred from near sea level along O‘ahu's windward coast to the uppermost reaches of the Ko‘olau Mountains. From there, snails were also distributed across the central plain of the island and through the Wai‘anae Mountains. However, since Polynesian and European settlement of O‘ahu, most forests below about 300 meters (1,000 feet) in elevation have been cleared for agricultural purposes. By 1900, the native vegetation and microclimates necessary to sustain Achatinella populations were absent from low elevation areas. Since the turn of the century, populations of Achatinella have been found only at elevations above approximately 300 meters (1,000 feet) in native Hawaiian shrublands and forests. Achatinella species seem to be most abundant in higher elevation ravines and upper ridges (USFWS 1993c).
The current range and abundance of Achatinella species is difficult to assess due to the continuing rapid reduction in their numbers, the lack of recent comprehensive surveys, and taxonomic difficulties at the species level. According to the USFWS (1993c), A. mustelina (shown in the figure above) is the most abundant of the Oahu Tree Snails. This species is restricted to the Wai‘anae Mountains. The next most abundant tree snail species, A. sowerbyana, is found in the northern Ko‘olau Mountains. With one exception, A. concavospira, the other extant Achatinella species are restricted to the Ko‘olau Mountains. Usually only two or three snails are found in a single bush or tree. For all Achatinella species, bushes or trees containing snails are often widely separated (USFWS 1993c).
Biology: Achatinella species are arboreal, spending almost their entire lives in trees and/or bushes where they feed on fungi scraped from the surfaces of leaves. The snails occur primarily on native vegetation, but are occasionally seen on alien plants. However, it is not known if alien plants can support healthy breeding populations of tree snails (USFWS 1993c). Achatinella species are also predominantly nocturnal, preferring cool and/or humid conditions when moving about. During the day, they usually seal themselves to leaves or trunks and remain motionless until nightfall (USFWS 1993c).
Individuals are hermaphroditic. A single embryo is usually present in the uterus of adults, and embryos are found at all times of the year. The young are born live and coexist with the adults (USFWS 1993c). Studies of A. mustelina revealed that adults reach sexual maturity at approximately 7 years of age and give birth to one to four young per year. Offspring are about 4.5 millimeters long at birth (Hadfield and Mountain 1980, Hadfield 1986, USFWS 1993c).
