Species fact sheet

SPECIES FACT SHEET

Class: Gastropoda

Order: Stylommatophora

Family: Polygyridae

Both the Forest Service and BLM have listed the Siskiyou hesperian as a Sensitive Species in Oregon.

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  Oregon State Rank: S1; critically imperiled
  

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  Washington State Rank: None
  
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  National Rank: N2; vulnerable to extirpation or extinction
  
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  Global Rank: G2; imperiled throughout its range
  

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  Oregon State Status: None
  
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  Washington State Status: None
  

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  None
  

The Siskiyou hesperian is a small, thin-shelled, brown Vespericola, with a moderately low spire, 5 ½ whorls in diameter and 8.4 to 9.0 mm. Sculpture of regular, dot-like papillae on post-embryonic whorls, bearing minute periostracal setae over most of the shell. Radial growth lines numerous and resembling fine ribbing under a hand lens. Apertural lip light brown, thickened, reflected; narrowed below the pillar, then slightly flaring again. Umbillicus small but distinct, diameter 0.6 to 0.8 mm., sometimes with slight thickening at base, occasionally narrow crescentric parietal tooth seen. Resembles Trilobopsis loricata species found in this region, and more closely resembles Cryptomastix germana, but is distinctly umbillicate and lacks additional apertural teeth (Pilsbry 1946).

The Siskiyou hesperian is a freshwater riparian associate terrestrial snail. The biology of this species is not well understood.

The Siskiyou hesperian was originally found throughout southern Oregon, northern California, and northern Nevada at broadly scattered sites. Today it is found in northern California and southern Oregon. Distribution in Oregon includes sites near Upper Klamath Lake, Crater Lake National Park, and the Klamath River drainage in the Rogue River National Forest and Medford District BLM (Frest and Johannes 1995, Roth 1993).

The Siskiyou hesperian is primarily a riparian associate found in perennially moist habitat, including spring seeps and deep leaf litter along streambanks and under debris and rocks. Moist valley, ravine, gorge, or talus sites are preferred, near the lower portions of slopes in areas that are not subject to regular flooding. It may occur in areas with running water or alongside streams and spring pools (Frest and Johannes 1995, Roth 1993].

Threats to the Siskiyou hesperian include the diversion or modification of springs for livestock watering and irrigation. Human use may result in loss or degradation of habitat. Removal of forest overstory from logging can dry important subterranean refugia and loss of aestivating individuals. Concentrated use of riparian areas by livestock may also degrade habitat, as can development for agriculture or human use (Frest and Johannes 2000).

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  Survey and map all Siskiyou hesperian occurrences.
  

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  Protect this species’ habitat from further destruction and restore it when opportunities are presented.
  

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  Monitor and assess activities for impacts on the Siskiyou hesperian and its habitat.
  

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  Minimize or eliminate conversion of habitat for other uses
  

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  Monitor the effects of habitat changes on this species
  

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  The use of insecticides or herbicides may negatively affect this species. If insecticide or herbicide use is planned for areas where the Siskiyou hesperian occurs, utilize available resources to assess alternatives to their use.
  

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  Minimize livestock use at known sites.
  

The Siskiyou hesperian has been found in association with other Vespericola species, Prophysaon, Oxyloma, and Deroceras (Frest and Johannes 1995).

forests in the range of the northern spotted owl. Prepared for: Forest Ecosystem