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Montana Field Guide

Montana Field Guides

Lyre Mantleslug - Udosarx lyrata

Species of Concern
Native Species

Global Rank: G3
State Rank: S1

Agency Status

External Links

General Description
A small slug, animals may reach 30 mm or more, but are often smaller. Body and mantle base-color is cream, head and lateral grooves (7-8) on the body are dark to black, the latter highlighting a mid-dorsal tawny strip on the tail. The posterior margin of the mantle is deeply notched, similar to Zacoleus, and the pneumostome is present above or anterior to the mantle cleft. The mantle covers less than half the body, and has blackish lateral lines on the posterior half that converge towards the posterior margin, with small black spots on the anterior half of the mantle vaguely delineating a grid pattern. The right mantle line is sometimes more sinuous than the left, and the two converging lines form a lyreshaped symbol—hence the species name, lyrata. The back has a prominent keel especially noticeable in contracted individuals. The sole is tripartite (having two longitudinal furrows); the mucous is clear (Hendricks 2012, Burke 2013). Internal anatomy is described by Webb (1959) and Russell and Webb (1980).

There may be two subspecies in Montana. U. l. lyrata: from specimens collected 4.0 km west of the crest of Lolo Pass, Clearwater County, Idaho (Webb 1959); U. l. russelli: from specimens collected 1.6 km west of Potomac, Missoula County, Montana (Russell and Webb 1980). The taxonomic validity of these subspecies needs reevaluation.

Diagnostic Characteristics
A combination of size, coloration, mantle markings, and overall morphology readily distinguish this species from other slugs. The sole of the foot is tripartite (having two longitudinal furrows best seen when the animal crawls on a clear surface), a strongly keeled back (most prominent when the animal is more or less contracted), a small notch on the right posterior mantle margin, a pneumostome (breething pore) above or anterior to the mantle cleft. The similar sheathed slug (Zacoleus idahoensis) shares these traits, but Udosarx has a bluish-gray to cream base color with a contrasting blackish head and dark grooves on the upper surface of the tail demarcating rows of tubercles, and a pair of dark lateral lines on the mantle that converge posteriorly.

Species Range
Montana Range


Range Comments
Northern Idaho and adjacent northwestern Montana west of the Continental Divide (Burke 2013). In Montana, 19 records in three counties: Mineral (5), Missoula (5), Ravalli (9). Elevation range is 928 to 2542 m (3045 to 8340 ft). May be locally abundant; up to 17 individuals were found at one Missoula County site in early May (Hendricks 2012).

Observations in Montana Natural Heritage Program Database
Number of Observations: 20

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Predicted Distribution in Montana
Predicted distribution model for Lyre Mantleslug (Udosarx lyrata). Records were spatially unique and had a locational uncertainty of ≤ 400 meters.  Hotter colors indicate areas that are predicted to have more suitable habitat for the species.  Black dots are positive data used to build the model.  Gray dots are locations where a survey capable of detecting the species has been performed.  Landownership, a shaded relief map, and county lines are included for reference.  Details of the modeling effort, a description of the environmental layers used, and a more thorough interpretation of model outputs can be found in the report Land Mollusk Surveys and Predicted Distribution Models on USFS Northern Region Lands: 2007.

Predicted Distribution Map

More model output for this species
Mostly mesic mixed conifer forest and riparian woodlands, sometimes with talus, also at higher elevation in drier habitat where snow banks and seeps keep soil moister. Canopy species include Engelmann spruce, subalpine fir, whitebark pine, Douglas-fir, ponderosa pine, lodgepole pine, western larch, western hemlock, western redcedar, black cottonwood and paper birch, secondary canopy includes alder, willow, mountain maple, and dogwood. Usually found under rocks and woody debris, sometimes within rotten logs (Hendricks 2012).

Reproductive Characteristics
Courtship and copulation have been observed in captive animals in November (Russell and Webb 1980).

  • Literature Cited AboveLegend:   View Online Publication
    • Burke, T. E. 2013. Land snails and slugs of the Pacific Northwest. Corvallis, OR: Oregon State University Press. 344 p.
    • Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.
    • Russell, R.H. and G.R. Webb. 1980. The slug Udosarx lyrata: additional data on distribution, anatomy, and taxonomy. Gastropodia 2: 8-10.
    • Webb, G.R. 1959. Two new north-western slugs, Udosarx lyrata and Gliabates oregonia. Gastropodia 1:22-23, 28.
  • Additional ReferencesLegend:   View Online Publication
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    • Frest, T.J. and E.J. Johannes. 1995. Interior Columbia Basin mollusk species of special concern. Final report to the Interior Columbia Basin Ecosystem Management Project, Walla Walla, WA. Contract #43-0E00-4-9112. 274 pp. plus appendices.
    • Frest, T.J. and E.J. Johannes. 2001. An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Science 36(2):1-51.
    • Hendricks, P. 2003. Status and conservation management of terrestrial mollusks of special concern in Montana. Unpublished report prepared for the U.S. Forest Service. Montana Natural Heritage Program, Helena, Montana. 67 pp. + appendices.
    • Hendricks, P., B.A. Maxell, and S. Lenard. 2006. Land mollusk surveys on USFS Northern Region lands. A report to the USDA Forest Service, Northern Region. Montana Natural Heritage Program, Helena, Montana. 11 pp. plus appendices.
    • Hendricks, P., B.A. Maxell, S. Lenard, and C. Currier. 2007. Land mollusk surveys on USFS Northern Region lands: 2006. A report to the USDA Forest Service, Northern Region. Montana Natural Heritage Program, Helena, Montana. 11 pp. plus appendices.
    • Hendricks, P., B.A. Maxell, S. Lenard, and C. Currier. 2008. Surveys and predicted distribution models for land mollusks on USFS Northern Region Lands: 2007. Report to the USDA Forest Service, Northern Region. Helena, MT: Montana Natural Heritage Program. 12 pp. + appendices.
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Citation for data on this website:
Lyre Mantleslug — Udosarx lyrata.  Montana Field Guide.  .  Retrieved on , from