Hawaiʻi’s terrestrial snails are an astonishing example of radiation. Of the over 700 species documented, 98% are endemic to Hawaiʻi. A DLNR 2015 SWAP factsheet for landsnails is here: https://dlnr.hawaii.gov/wildlife/files/2019/02/SWAP-2015-Stylommatophora-Snails-Final.pdf. A snip from the factsheet is below.
For an overview and comparison of total numbers of Gastropods in Hawaiʻi, the numbers below are an extract from the 2003 Bishop Museum species summary publication by Eldredge and Evenhuis: http://hbs.bishopmuseum.org/pubs-online/pdf/op76.pdf.
The number of terrestrial and freshwater gastropods were given as 831 (759 endemic, and 63 non-idigenous) and 37+ (7 endemic and 22 non-indigenous), respectively(sources were listed as Cowie et al 1995, Cowie 1997, and Cowie, pers. Comm). New species are still being discovered! A July 2020 paper by Yeung et al. describes a new species of land snail. The study can be found here: https://zookeys.pensoft.net/article/50669/.
Tree snails in the genus Achatinella are one group of terrestrial snails in the family Achatinellidae and they have received the most attention and protection, likely because of the beauty of their shells. A description of this group is on the Quick Overview page here: https://hawaiibiodiversity.org/a-look-at-some-unique-and-amazing-places-plants-animals/. Additional information on this genus is shown in the excerpt below from the 2015 DLNR factsheet, with the full factsheet available here: https://dlnr.hawaii.gov/wildlife/files/2019/02/SWAP-2015-Oahu-tree-snails-Final.pdf.
Hawaiian snails were studied by several dedicated biologists early on in Hawaiʻi and they published the Manual of Conchology with volumes from 1885-1935. They can be accessed at: https://www.biodiversitylibrary.org/bibliography/6534#/summary.
The Bishop museum Malacology Dept. has a searchable Hawaiian Freshwater & Terrestrial Mollusk Checklist Database here: http://data.bishopmuseum.org/HBS/checklist/query.asp?grp=Mollusk
A detailed account of the Hawaiian land snail fauna and conservation issues is laid out in a 2018 paper by N. Yeung and K. Hayes at the Bishop museum titled Biodiversity and Extinction of Hawaiian Land Snails: How Many Are Left Now and What Must We Do To Conserve Them-A Reply to Solem available here: https://academic.oup.com/icb/article/58/6/1157/5032875.
Here is a short excerpt from the paper that summarizes the conservation challenges: “Solem proposed actions necessary for conservation in four phases: (1) use the extensive collections in natural history museums to develop a baseline of the identity, historical distribution, and abundance of species; (2) use these data to organize and carryout extensive field surveys to identify the remaining taxa and their habitats; (3) develop approaches to protect and expand suitable habitat by identifying immediate threats to the remaining taxa and their habitats; and(4) complete systematic revisions of all 10 families to serve as a basis for conservation and further research. To these we add a fifth phase, changing peoples’ perceptions and appreciation of invertebrates, which is critical for saving the lesser known and underappreciated faunas of Pacific Islands, and beyond”.
An earlier 2015 paper by C. Regnier et al. Extinction in a hyperdiverse endemic Hawaiian landsnail family and implications for the underestimation of invertebrate extinction encapsulates the dire nature of the conservation status of Hawaiʻi’s land snails, and in particular for this paper one family: “Of the 325 Amastridae species, 43 were originally described as fossil or subfossil and were assumed to be extinct. Of the remaining 282, we evaluated 88 as extinct and 15 as extant and determined that 179 species had insufficient evidence of extinction (though most are probably extinct).” The paper is available here: https://sciences.ucf.edu/biology/king/wp-content/uploads/sites/106/2011/08/cobi12565.pdf.
Estimates of Hawaiʻi’s land snail species numbers over time indicates the rarity of some species and how some species are being rediscovered. This is shown figure below which are from a Dr. Norine Yeung (Malacology Curator at Bishop Museum) presentation on November 13, 2019 for the University of Hawaiʻi Natural Resources and Environmental Management Research Seminar Series.
Dr. Yeung’s presentation also included numbers by family as shown in the figure below.
The DLNR Division of Forestry and Wildlife has a Snail Extinction Prevention (SEP) program. Their website is here: https://dlnr.hawaii.gov/ecosystems/hip/sep/.
An example of a study trying to determine some life history of one species, Demographic Studies on Hawaiʻi’s Endangered Tree Snails: Partulina proxima, by Hadfield and Miller in 1989 is here: https://pdfs.semanticscholar.org/1c1e/e4b45c08d761a05e8c7fa8dcbbd3eb278778.pdf. This species is in the same subfamily as the listed Achatinella species.