Nineteen Species of Terrestrial Mollusks Found in Park

This article was originally published in The Midden – Great Basin National Park: Vol. 19, No. 2, Winter 2019.

One of the many terrestrial mollusks found in Great Basin National Park. This species is
the Great Basin Mountain Snail, Oreohelix strigosa depressa.

Photo by Mark Ports

by Mark Ports, retired professor, Great Basin College

Land snails and slugs existing in the Great Basin desert may seem like a paradox with valleys of salt flats, rivers that sink into the ground, and long miles between high mountain ranges. However, in Great Basin National Park there exists today, although small and inconspicuous, 18 species of land snails and one species of slug.

During the period of spring 2014 through the summer of 2016 a survey was carried out to identify these rarely seen invertebrates found in the national park. Over 60 localities, including canyons, upland wooded slopes and mountain brush, riparian woodlands, subalpine lakes, and Bristlecone forests were sampled for terrestrial mollusks. The survey showed that land snails were most diverse and abundant with 15 species located in wooded riparian below limestone cliffs such as at the Grey Cliffs on Baker Creek.

Limestone in the form of calcium carbonate is used for shell development. Mesic litter found beneath shrubs and aspen provide food for these herbivorous species and retains moisture for their mucus used to move about on their single foot. Riparian habitats with deciduous vegetation, moist litter, and rockslides can contain a community of 8 to 12 species of land snails. Rockslides provide a deep, moist sanctuary from the heat of summer and the cold of winter. Boggy stream sides and wet springs will provide habitat for up to 11 species of land snails plus the only species of slug, Derocerus laeve and a water-dependent land snail, the ambersnails of the family Succiniedae.

The highest elevation known to be used by land snails is found in the rocky habitat of Bristlecone woodlands at 3200 meters. Here only 1 to 3 species were found, while the lowest elevation at 1800 m in sagebrush-steppe supported only 2 species. The dry, barren ground of much of the Pinyon Pine and Utah Juniper woodland apparently would not support any land snail species.

Most species of land snails inhabiting the park today are considered tiny, ranging from 2-6 mm in diameter such as the Montane Snaggletooth (Gastrocopta pilsbryana) and the Crestless Column (Pupilla hebes). The largest land snails include species of Mountainsnails (Oreohelicidae), such as the Schell Creek Mountainsnail (Oreohelix nevadensis), endemic to Nevada, and the Great Basin Mountainsnail (Oreohelix strigosa depressa), found in the mountains of eastern Nevada and many of the mountains of Utah and Colorado. These large snails, 10-20 mm in diameter, are found in localized colonies in rockslides, sheltered by deciduous shrubs, aspen, and conifers.

Closeup of one of the Montane Snaggletooth, only 2 mm long.

Photo by Mark Ports

It appears that the terrestrial mollusks of the national park have close affinities with the terrestrial mollusks of northeastern Nevada, such as those found in the Ruby Mountains and share many species with the land snails found today in the Wasatch Mountains of Utah. The terrestrial mollusks found in the park today are probably the remnants of a once widespread mollusk community found throughout the Great Basin and the Rocky Mountains during the wetter Pleistocene (2 mya). They have now retreated to higher elevations providing mesic habitats available in the moist, wooded mountains since the dry Holocene over the last 50,000 years.

Today these invertebrates are limited to small and specialized habitats, with climate change and human disturbance making their future uncertain. For references and details: Ports, M.A. 2019. Terrestrial mollusks of Great Basin National Park, the Snake Range, Nevada, USA. Western North American Naturalist 79(2): 247-259.