Discus macclintocki

Iowa Pleistocene snail
A live Iowa Pleistocene snail
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
(unranked): clade Heterobranchia

clade Euthyneura
clade Panpulmonata
clade Eupulmonata
clade Stylommatophora
informal group Sigmurethra

Superfamily: Punctoidea
Family: Discidae
Genus: Discus
Species: D. macclintocki
Binomial name
Discus macclintocki
(F. C. Baker, 1928)

The Iowa Pleistocene snail, also known as the Pleistocene disk, scientific name Discus macclintocki, is a very small air-breathing land snail, a terrestrial pulmonate gastropod mollusk.

This snail now occurs nowhere else in the world but a few specialized locations: 37 algific talus slopes in Iowa and Illinois[1]. Algific talus slopes are areas of talus or scree that are "cold-producing", in other words they are part of a natural air-exchange system that renders the microclimate there colder than it is in the immediately surrounding areas. This is a relict species from the ice age and cannot survive in warmer areas.

The Iowa Pleistocene snail is an endangered species, in danger of becoming extinct.[2] [3]



This very small snail makes its home on cool rocky slopes, near the coldwater streams, cliffs, valleys, and sinkholes that make up the Driftless Area National Wildlife Refuge in Iowa.

Known from fossil records to have existed 400,000 years ago, it is one of many glacial relict species that found refuge in the region of northeast Iowa, northwest Illinois, southeast Minnesota, and southwest Wisconsin called the driftless area. The rugged seemingly driftless area was so called because of the inability of early geologists to find evidence of glacial drift. Much of the area was indeed covered by glaciers about 500,000 years ago.[4]

The Iowa Pleistocene snail found its current home with desirable temperature, moisture, and food resources about 10,000 years ago as ice age conditions moderated. Certain slopes, usually north facing, have loose rock that allows ice-cooled air to exit from underground cracks and fissures. Upland sinkholes contribute to the air flow regime and are an important component of a unique system called an algific talus slope, meaning cold producing rocky slope. Even when outside air temperature is 90 °F (32 °C), ground temperatures on these slopes can be close to freezing. This air flow provides a climate similar to what was prevalent in glacial eras. Freezing winter temperatures are moderated on the slopes giving a year round range of about -10 to 10 °C (14 to 50 °F).

The Iowa Pleistocene snail was thought to be extinct, until it was discovered in 1955 by a scientist working in northeast Iowa. It was listed as endangered in 1978.


The shell of this snail is no bigger than a shirt button, with adults ranging in size from 5 to 7 millimeters in diameter. They live in the leaf litter preferring a diet of birch and maple leaves. The snail shares its habitat with a host of rare and disjunct plants and animals associated with cool habitats. Balsam fir (Abies balsamea), Canada yew (Taxus canadensis) and yellow birch (Betula alleghaniensis) are common to algific talus slopes. The threatened Northern monkshood plant (Aconitum noveboracense) also grows on these sites.

The 775-acre (3.14 km2) Driftless Area National Wildlife Refuge was established in 1989 to permanently protect populations of the Iowa Pleistocene snail and threatened Northern monkshood. These species’ habitat cannot be restored if it is damaged and lost, and the primary objective of their respective recovery plans is providing protection for remaining colonies. The invasion of garlic mustard (Alliaria petiolata) onto algific talus slopes has emerged as a threat in recent years.

The Refuge consists of scattered tracts of land in northeast Iowa ranging from 6 to 208 acres (0.024 to 0.84 km2). Algific talus slopes range in size from a few square meters to perhaps a 12-mile (800 m) in length. More than just the algific talus slope is targeted for acquisition. Sinkholes that feed the system can occur some distance away from the slope and need protection to ensure long term integrity of the site. Buffer areas around the slope are included when possible. The Refuge contributes to lands already protected by The Nature Conservancy, the Iowa Department of Natural Resources, County Conservation Boards in Iowa, and publicly owned sites in Ohio and New York.

At least eight other snail species, considered glacial relicts, are also protected on these sites. Some of these species like the midwest pleistocene vertigo (Vertigo hubricti hubricti), are even smaller and perhaps more rare than the Iowa Pleistocene Snail. Protection of algific talus slopes may help prevent the need for threatened or endangered status for these snails and plants like the golden saxifrage (Chrysosplenium iowense).

Several Iowa Pleistocene Snails on leaves.
  • Appearance - These small land snails are only about 14 inches (6.35 mm) in diameter. Their shells are brown or greenish white.
  • Habitat - The snails live in the leaf litter of special cool and moist hillsides called algific talus slopes. Cool air and water, from underground ice, flow out of cracks in the slopes and keep the ground temperatures below 50 °F (10 °C) in summer and above 14 °F (−10 °C) in winter.
  • Reproduction - Iowa Pleistocene snails breed from late March to August. Two to six eggs are laid among the leaf litter and hatch in about 28 days. The snail's life span is about five to seven years.
  • Feeding Habits - The snails eat the fallen leaves of birch and maple trees and dogwood shrubs.
  • Range - These snails have only been found at about 30 sites in Iowa and Illinois. Fossilized shells indicate they were once much more widespread during cooler glacial periods.

Causes of endangered status

  • Habitat Loss or Degradation - The major long-term cause of snail population decline is climate change. The most immediate habitat threats are from logging, quarrying, road building, sinkhole filling and contamination, human foot traffic, livestock grazing and trampling, and misapplication of pesticides.


  • The Iowa Pleistocene snail was listed as an endangered species in 1978.
  • The Driftless Area National Wildlife Refuge was created to protect this snail and a plant.
  • Habitat Protection - The U.S. Fish and Wildlife Service, state, county, and private conservation agencies are all working to preserve the snail and its habitat. Some private landowners have entered into voluntary protection agreements.


  1. ^ Frest (2004). Discus macclintocki. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 10 May 2006. Database entry includes justification for why this species is of least concern
  2. ^ "Iowa Pleistocene Snail fact sheet". http://www.fws.gov/midwest/endangered/Snails/iops_fct.html. Retrieved August 8, 2005. 
  3. ^ "Species Profile for Iowa Pleistocene snail". http://ecos.fws.gov/species_profile/servlet/gov.doi.species_profile.servlets.SpeciesProfile?spcode=G00T. Retrieved August 8, 2005. 
  4. ^ "Iowa Pleistocene snail, Links, Endangered Species: U.S. Fish & Wildlife Service, Links, Endangered Species: U.S. Fish & Wildlife Service". http://www.fws.gov/endangered/i/G03.html. Retrieved August 8, 2005. [dead link]
  5. ^ "Driftless Area National Wildlife Refuge: U.S. Fish and Wildlife Service". Archived from the original on April 16, 2005. http://web.archive.org/web/20050416215521/http://www.fws.gov/midwest/Driftless/mcgdps.html. Retrieved August 8, 2005. 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Discus (gastropod) — Discus A live Discus rotundatus A live …   Wikipedia

  • Discus (genre) — Pour les articles homonymes, voir Discus. Discus …   Wikipédia en Français

  • Discus (genus) — Taxobox name = Discus status = status ref = trend = image width = 160px image caption = Discus macclintocki regnum = Animalia phylum = Mollusca classis = Gastropoda subclassis = Orthogastropoda superordo = Heterobranchia ordo = Pulmonata subordo …   Wikipedia

  • Karst topography — is a landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Due to subterranean drainage, there may be very limited surface water, even to the absence of all rivers and… …   Wikipedia

  • Indicator species — An indicator species is any biological species that defines a trait or characteristic of the environment. For example, a species may delineate an ecoregion or indicate an environmental condition such as a disease outbreak, pollution, species… …   Wikipedia

  • Driftless Area National Wildlife Refuge — Coordinates: 42°41′00″N 91°07′30″W / 42.6833333°N 91.125°W / 42.6833333; 91.125 …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.