Montana Field Guide

A small slug, with individuals reaching about 25 mm extended, but often smaller. Base color is dark brown to blackish on the head, mantle and tail, sometimes with very small dark irregular spots. The mantle is oval, about 2/5 of the body length, has a series of concentric ridges somewhat like a fingerprint, and lacks a notch along the posterior margin. The pneumostome is posterior to the mantle cleft and on the right side. The tail is covered with a series of small furrows and elongated tubercles, and is slightly keeled near the posterior end. The sole is pale and tripartite (having two longitudinal furrows), the mucous is clear (McDonnell et al. 2009, Hendricks 2012, Burke 2013). Internal anatomy is described by Pilsbry (1948) and Forsyth (2004).

A combination of small size, lack of visceral mantle hump, concentric fingerprint-like ridges on the mantle, lack of notch in right posterior mantle margin, tripartite sole and unkeeled tail, and dark brown color separate this species from all others. Color, size, and production of clear mucous, even when disturbed, separate this species from the paler, mottled, and larger D. reticulatum.

Found in a variety of situations near moisture (wet meadows, marshes, streamside riparian), sometimes in sites without a tree canopy. Canopy tree species include a mixture of conifer and broadleaf types, including Engelmann spruce, Douglas-fir, lodgepole pine, black cottonwood, aspen, paper birch, ponderosa pine, western larch, western redcedar, western hemlock, rocky mountain juniper, with a secondary canopy including alder, willow, dogwood, and hawthorn. Most often found under woody debris and leaf litter, sometimes under rocks (Hendricks 2012).