Discus whitneyi - (Newcomb, 1864)
Forest Disc Snail
Other English Common Names: Forest Disc
Taxonomic Status: Accepted
Related ITIS Name(s): Discus whitneyi (Newcomb, 1864) (TSN 567505)
Unique Identifier: ELEMENT_GLOBAL.2.119891
Element Code: IMGAS54050
Informal Taxonomy: Animals, Invertebrates - Mollusks - Terrestrial Snails
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Gastropoda Stylommatophora Discidae Discus
Check this box to expand all report sections:
Concept Reference
Concept Reference: Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.
Concept Reference Code: B98TUR01EHUS
Name Used in Concept Reference: Discus whitneyi
Taxonomic Comments: This species was formerly listed as Discus cronkhitei, which was in wide use for over a century but was described a year later (Roth, 1987). There is some question as to whether this species will ultimately be shown to be a Western Hemisphere member of Discus ruderatus of northern Eurasian forests (Kerney and Cameron, 1979).
Conservation Status

NatureServe Status

Global Status: G5
Global Status Last Reviewed: 01Aug2017
Global Status Last Changed: 08Oct2002
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N5 (08Oct2002)
Nation: Canada
National Status: N5 (01Aug2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alaska (SNR), Arizona (SNR), Arkansas (SX), California (SNR), Connecticut (SNR), Delaware (SNR), Idaho (S4), Illinois (SNR), Indiana (SNR), Iowa (SNR), Kansas (SX), Kentucky (S3), Maine (SNR), Maryland (SNR), Massachusetts (SNR), Michigan (SNR), Minnesota (SNR), Missouri (SX), Montana (S5), Nebraska (SX), New Jersey (SNR), New Mexico (SNR), New York (SNR), North Carolina (S1S2), North Dakota (SNR), Ohio (SNR), Oklahoma (SX), Pennsylvania (S3S4), South Dakota (SNR), Texas (SX), Utah (S5), Vermont (SNR), Virginia (S3), Washington (S5), West Virginia (S2), Wisconsin (S3), Wyoming (SNR)
Canada Alberta (S5), British Columbia (S5), Labrador (S5), Manitoba (S4), New Brunswick (S5), Newfoundland Island (S5), Northwest Territories (S4), Nova Scotia (SU), Prince Edward Island (SU), Quebec (SNR), Saskatchewan (S4), Yukon Territory (S4)

Other Statuses

NatureServe Global Conservation Status Factors

Number of Occurrences: > 300
Number of Occurrences Comments: Forsyth (2005) documented it in the Upper Fraser Basin of central British Columbia where it is widespread and common, much like the rest of British Columbia, except along the coast. Most recently, it was discovered in the Ktunaxa Traditional Territory in southeastern British Columbia (which extends from near Canada - U.S. border north to about 50 km north of Cranbrook) (Ovaska and Sopuck, 2009). In Alberta it is distributed in the southern 2/3 of province from Fairview and reported in all natural regions except the Canadian Shield (Lepitzki, 2001). It occurs in eastern Maine (5 of 101 sites) where it is rare when found in upland sites and is very uncommon except for a few areas immediately adjacent to the coast (Nekola, 2008). In New York, Hotopp and Pearce (2007) report it from most counties except northeastern New York. Baxter (1987) cites occurrences in Alaska in the North Gulf Coast and southwestern Alaska, with potential occurrences elsewhere; including Attu (Aleutian Islands) (Roth and Lindberg, 1981). In Arizona, it was documented in Arch Canyon in Organ Pipe Cactus National Monument, just north of the Mexican border (Dillon, 1980).

Other NatureServe Conservation Status Information

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AK, ARextirpated, AZ, CA, CT, DE, IA, ID, IL, IN, KSextirpated, KY, MA, MD, ME, MI, MN, MOextirpated, MT, NC, ND, NEextirpated, NJ, NM, NY, OH, OKextirpated, PA, SD, TXextirpated, UT, VA, VT, WA, WI, WV, WY
Canada AB, BC, LB, MB, NB, NF, NS, NT, PE, QC, SK, YT

Range Map
No map available.

Ecology & Life History
Habitat Type: Terrestrial
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Palustrine Habitat(s): Riparian
Terrestrial Habitat(s): Desert, Grassland/herbaceous, Shrubland/chaparral, Urban/edificarian
Special Habitat Factors: Burrowing in or using soil
Habitat Comments: In Arizona, this species has been found in shrubland desert canyons usually in deep loosely packed humus (Dillon 1980). In Kentucky, this species is found in low damp soils around open grassy places, roadsides, and edges of wetlands; also frequent in urban areas (Dourson 2010).
Economic Attributes Not yet assessed
Management Summary Not yet assessed
Population/Occurrence Delineation
Group Name: Terrestrial Snails

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Separation Barriers: Barriers include barriers to dispersal such as the presence of permanent water bodies greater than 30 m in width, permanently frozen areas (e.g. mountaintop glaciers) which generally lack land snails (Frest and Johannes, 1995), or dry, xeric areas with less than six inches precipitation annually, as moisture is required for respiration and often hatching of eggs. For the various slugs and slug-like species (families Arionidae, Philomycidae, Limacidae, Milacidae, Testacellidae, Veronicellidae), absence of suitable moisture, except for the most ubiquitous of species such as Deroceras reticulatum (Müller, 1774), can serve as a barrier to movement (Frest and Johannes, 1995). Members of these groups tend to have greater difficulty crossing areas of little moisture than other pulmonates. For tree snails (family Bulimulidae [= Orthalicidae]), lack of appropriate arboreal habitat (e.g. distance of greater than 500 m) also serves as a separation barrier.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 1 km
Alternate Separation Procedure: None
Separation Justification: Burch and Pearce (1990) suggest refuges may be the most important factor limiting terrestrial snail abundance, although the greatest richness of species among carbonate cliff habitats (one of the most diverse in North America) is associated with calcareous, as opposed to acidic, substrates (Nekola, 1999; Nekola and Smith, 1999). The panmictic unit (a local population in which matings are random) is small relative to those of other animal groups because terrestrial snails tend to be more sedentary. Baker (1958) claimed, "long-distance dispersal of terrestrial gastropods is undoubtedly passive" although short distance dispersal is active involving slow, short distance migration under favorable conditions. Long-distance passive migration is not considered when assigning separation distances, as otherwise separation distances for many animals and plants would be made impracticably large. Passive migration of snails on terrestrial mammals, birds, or insects may occur over longer distances may occur across barriers. Passive migration also may occur by wind or by rafting on floating objects (Vagvolgyi, 1975). A third form of passive migration may occur through human activity such as transport as food, with consumed goods, or for biological control of other organisms.

Terrestrial gastropods do not move much usually only to find food or reproduce. Olfaction is the primary sensory behavior utilized to find and move toward a food item (on the scale of cm to m) although Atkinson (2003) found that Anguispira alternata was capable of switching foraging behavior when snails encountered a physical barrier to movement. Fisher et al (1980) reported maximum movement rate of Rumina decollata (Linnaeus, 1758), an introduced pest species in California spreading relatively rapidly (for a snail), to be 20 m in three months (= 6.67 m/month) in an irrigated orchard. Tupen and Roth (2001) reported the movement rate for the same species in an un-irrigated native scrub on San Nicolas Island to be 0.4 km in 12 years (= 33.33 m/month). South (1965) found in dispersal studies of the slug, Deroceras reticulatum, that slugs traveled a mean distance of 1.13 m in seven days indicating this species disperses little throughout its life. Giokas and Mylonas (2004) found mean dispersal and minimal movement distances were very small (16.2 and 5.4 m, respectively) for Albinaria coerulea, with few individuals dispersing longer distances. Even the most extreme dispersal distances, such as 500 m for the giant African land snail Achatina fulica (Tomiyama and Nakane, 1993), do not approach the scale of km. Viable land snail populations generally occupy small areas. Frest and Johannes (1995) report the largest Oreohelix colony they observed was one mile (1.67 km) long and 0.25 miles (0.41 km) wide while the smallest was six feet (183 cm) long and two feet (61 cm) wide.

As a whole, pulmonates (previously Subclass Pulmonata) are better dispersers than prosobranchs (previously Subclass Prosobranchia) possibly due to their hermaphroditic reproduction increasing the chance of new colonization (Pilsbry, 1948). When compared with prosobranch families, pulmonates generally reproduce at smaller sizes and sooner, produce greater numbers of eggs/young, have larger clutch sizes, greater growth rates, and shorter life cycles (Brown, 1991). Further, prosobranchs' requirement of constant moisture for oxygen exchange limits their ability to colonize drier habitats. Suitable habitat for pulmonate groups tends to be more varied and less restrictive than for prosobranch groups. All of these factors contribute to pulmonates greater dispersal capability over prosobranchs, as evidenced by the wider and more varied distribution of pulmonates over prosobranchs. Despite this, separation distance for both groups is set at the minimum one km as most movements are well within this suggested minimum separation distance.

Date: 26May2004
Author: Cordeiro, J.
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
NatureServe Conservation Status Factors Edition Date: 15Feb2008
NatureServe Conservation Status Factors Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 06Mar2008
Element Ecology & Life History Author(s): Cordeiro, J.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

  • Baxter, R. 1987. Mollusks of Alaska: a listing of all mollusks, freshwater, terrestrial, and marine reported from the State of Alaska, with locations of the species types, maximum sizes and marine depths inhabited. Shells and Sea Life, Bayside, California. 163 pp.

  • Catling, P.M. and B. Kostiuk. 2018. Snails and Slugs of the Northwest Territories. Published Privately. 29 pp.

  • Dillon, R.T., Jr. 1980. Multivariate analysis of desert snail distribution in an Arizona canyon. Malacologia, 19(2): 201-207.

  • Dourson, D C. and West Virginia DNR. 2015. Land snails of West Virginia. Goatslug Publications, Bakersville, North Carolina. 412 pp.

  • Dourson, D.C. 2010. Kentucky's land snails and their ecological communities. Goatslug Publications, Bakersville, NC. 298 pp.

  • Forsyth, R. 2014. General Status rank assessment of the terrestrial molluscs of British Columbia. Prepared for Canadian Wildlife Service, Environment Canada. Gatineau, PQ.

  • Forsyth, R.G. 2005a. Terrestrial gastropods of the Upper Fraser Basin of British Columbia. Living Landscapes, Royal British Columbia Museum: Victoria, British Columbia. 26 pp.

  • Forsyth, Robert G. 2006. An annotated checklist (based mostly on literature records) and bibliography of the recent terrestrial mollusca of Alberta. Unpublished report.

  • General Status 2015, Environment Canada. 2015. Manitoba Mollusk species list and subnational ranks proposed by an expert.

  • Godin, B, and D. Davidge. 2013. Benthic Information System for the Yukon (BISY). Environment Canada, Whitehorse, Yukon. unpublished database.

  • Hotopp, K. and T.A. Pearce. 2007. Land snails in New York: statewide distribution and talus site faunas. Final Report for contract #NYHER 041129 submitted to New York State Biodiversity Research Institute, New York State Museum, Albany, New York. 91 pp.

  • Kerney, M.P. and R.A.D. Cameron. 1979. Field Guide to the Land Snails of the British Isles and Northwestern Europe. Collins Press, London, England.

  • Lepitzki, D.A.W. 2001. Gastropods: 2000 preliminary status ranks for Alberta. Unpublished report prepared for Alberta Sustainable Resource Development, Fish and Wildlife Division, Edmonton, Alberta. 126 pp.

  • Nekola, J.C. 2008. Land snail ecology and biogeography of eastern Maine. Final report submitted to: Maine Department of Inland Fisheries & Wildlife and the Aroostook Hills and Lowlands Inventory, January 27, 2008. 119 pp.

  • Ovaska, K. and L. Sopuck. 2009. Surveys for terrestrial gastropods at risk within Ktunaxa Traditional Territory. Report prepared for British Columbia Ministry of Environment, Victoria, British Columbia. 27 pp.

  • Pilsbry, H.A. 1948. Land Mollusca of North America (north of Mexico). Monograph of the Academy of Natural Sciences of Philadelphia, 2(2): 521-1113.

  • Roth, B. 1987. Identities of two Californian land mollusks described by Wesley Newcomb. Malacological Review, 20: 129-132.

  • Roth, B. and D.R. Lindberg. 1981. Terrestrial mollusks of Attu, Aleutian Islands, Alaska. Arctic, 34(1): 43-47.

  • Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.

  • Wildlife Management Information System (WMIS). 2006+. Geo-referenced wildlife datasets (1900 to present) from all projects conducted by Environment and Natural Resources, Government of the Northwest Territories, Canada.  Available at http://www.enr.gov.nt.ca/programs/wildlife-research/wildlife-management-information-services

Use Guidelines & Citation

Use Guidelines and Citation

The Small Print: Trademark, Copyright, Citation Guidelines, Restrictions on Use, and Information Disclaimer.

Note: All species and ecological community data presented in NatureServe Explorer at http://explorer.natureserve.org were updated to be current with NatureServe's central databases as of March 2019.
Note: This report was printed on

Trademark Notice: "NatureServe", NatureServe Explorer, The NatureServe logo, and all other names of NatureServe programs referenced herein are trademarks of NatureServe. Any other product or company names mentioned herein are the trademarks of their respective owners.

Copyright Notice: Copyright © 2019 NatureServe, 2511 Richmond (Jefferson Davis) Highway, Suite 930, Arlington, VA 22202, U.S.A. All Rights Reserved. Each document delivered from this server or web site may contain other proprietary notices and copyright information relating to that document. The following citation should be used in any published materials which reference the web site.

Citation for data on website including State Distribution, Watershed, and Reptile Range maps:
NatureServe. 2019. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available http://explorer.natureserve.org. (Accessed:

Citation for Bird Range Maps of North America:
Ridgely, R.S., T.F. Allnutt, T. Brooks, D.K. McNicol, D.W. Mehlman, B.E. Young, and J.R. Zook. 2003. Digital Distribution Maps of the Birds of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Bird Range Maps of North America:
"Data provided by NatureServe in collaboration with Robert Ridgely, James Zook, The Nature Conservancy - Migratory Bird Program, Conservation International - CABS, World Wildlife Fund - US, and Environment Canada - WILDSPACE."

Citation for Mammal Range Maps of North America:
Patterson, B.D., G. Ceballos, W. Sechrest, M.F. Tognelli, T. Brooks, L. Luna, P. Ortega, I. Salazar, and B.E. Young. 2003. Digital Distribution Maps of the Mammals of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Mammal Range Maps of North America:
"Data provided by NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy-Migratory Bird Program, Conservation International-CABS, World Wildlife Fund-US, and Environment Canada-WILDSPACE."

Citation for Amphibian Range Maps of the Western Hemisphere:
IUCN, Conservation International, and NatureServe. 2004. Global Amphibian Assessment. IUCN, Conservation International, and NatureServe, Washington, DC and Arlington, Virginia, USA.

Acknowledgement Statement for Amphibian Range Maps of the Western Hemisphere:
"Data developed as part of the Global Amphibian Assessment and provided by IUCN-World Conservation Union, Conservation International and NatureServe."

NOTE: Full metadata for the Bird Range Maps of North America is available at:

Full metadata for the Mammal Range Maps of North America is available at:

Restrictions on Use: Permission to use, copy and distribute documents delivered from this server is hereby granted under the following conditions:
  1. The above copyright notice must appear in all copies;
  2. Any use of the documents available from this server must be for informational purposes only and in no instance for commercial purposes;
  3. Some data may be downloaded to files and altered in format for analytical purposes, however the data should still be referenced using the citation above;
  4. No graphics available from this server can be used, copied or distributed separate from the accompanying text. Any rights not expressly granted herein are reserved by NatureServe. Nothing contained herein shall be construed as conferring by implication, estoppel, or otherwise any license or right under any trademark of NatureServe. No trademark owned by NatureServe may be used in advertising or promotion pertaining to the distribution of documents delivered from this server without specific advance permission from NatureServe. Except as expressly provided above, nothing contained herein shall be construed as conferring any license or right under any NatureServe copyright.
Information Warranty Disclaimer: All documents and related graphics provided by this server and any other documents which are referenced by or linked to this server are provided "as is" without warranty as to the currentness, completeness, or accuracy of any specific data. NatureServe hereby disclaims all warranties and conditions with regard to any documents provided by this server or any other documents which are referenced by or linked to this server, including but not limited to all implied warranties and conditions of merchantibility, fitness for a particular purpose, and non-infringement. NatureServe makes no representations about the suitability of the information delivered from this server or any other documents that are referenced to or linked to this server. In no event shall NatureServe be liable for any special, indirect, incidental, consequential damages, or for damages of any kind arising out of or in connection with the use or performance of information contained in any documents provided by this server or in any other documents which are referenced by or linked to this server, under any theory of liability used. NatureServe may update or make changes to the documents provided by this server at any time without notice; however, NatureServe makes no commitment to update the information contained herein. Since the data in the central databases are continually being updated, it is advisable to refresh data retrieved at least once a year after its receipt. The data provided is for planning, assessment, and informational purposes. Site specific projects or activities should be reviewed for potential environmental impacts with appropriate regulatory agencies. If ground-disturbing activities are proposed on a site, the appropriate state natural heritage program(s) or conservation data center can be contacted for a site-specific review of the project area (see Visit Local Programs).

Feedback Request: NatureServe encourages users to let us know of any errors or significant omissions that you find in the data through (see Contact Us). Your comments will be very valuable in improving the overall quality of our databases for the benefit of all users.