Rediscovery of Discus brunsoni Berry, 1955 and Oreohelix alpina (Elrod, 1901) in the Mission Mountains, Montana : with comments on Oreohelix elrodi (Pilsbry, 1900) / Paul Hendricks.

Abstract

During summer 1997, extant populations of the endemic land snails Discus brunsoni and Oreohelix alpina were rediscovered near the type localities in the Mission Mountains, Montana; last known collections were made 33 and 48 years ago, respectively. D. brunsoni and Oreohelix elrodi (also endemic to the Mission Mountains and nearby Swan Range) were previously reported to be sympatric in subalpine limestone talus. Both species were found in 1997 in diorite talus; the latter species also occupied argillite talus with little, if any, limestone present at any site. Live D. brunsoni (n = 8) were found near the talus surface only on bare rock or foliose lichen on rock during cool, wet conditions. Live O. elrodi were found near the talus surface on rock (n = 9) or organic litter accumulations (n = 55) during all conditions, although in reduced number during warmer and drier weather. Above treeline, live O. alpina were found exclusively in exposed locations under limestone talus, sometimes attached to rock surfaces (n = 7) but more often present in organic detritus (n = 10). Lack of collections of D. brunsoni and O. alpina in recent decades probably resulted from 1) extremely restricted distributions, 2) limited knowledge of habitat requirements, and 3) scarcity of active collectors in the region.

Status and conservation management of terrestrial mollusks of special concern in Montana /

“…The type locality is the south-facing slope above McDonald Lake in the Mission Mountains Tribal Wilderness of the Confederated Salish and Kootenai Tribes, at about 1120 m (3700 ft) elevation. Several talus slopes are present above the north shore of the lake; indicates more than one slope is occupied, but Hendricks (1998) found D. brunsoni only in the talus slope where diorite was abundant.…”

“…Maximum diameter of holotype 10.5 mm, minimum diameter 9.1 mm; height of shell 4.2 mm, diameter of umbilicus 3.5 mm. Maximum diameters of eight live individuals measured by Hendricks (1998) ranged from 6.7 mm to 10.5 mm (mean = 9.5 ± 1.4 mm).…”

“…Vegetation at the margins of the talus slopes includes Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), pockets of water birch (Betula occidentalis), quaking aspen (Populus tremuloides), and mock orange (Philadelphus lewisii). Rock composition at the type locality was described as limestone (Berry 1955, Frest and, but more recent examination (Hendricks 1998) revealed the occupied talus to be a mix of diorite and argillite with no limestone present. Apparently this species retreats deep into the talus when surface conditions are unfavorable.…”

“…suggested that D. brunsoni may be crepuscular or nocturnal near the surface, because many collections were made shortly before dusk, or at least in subdued light, following intensive mid-day searches. Hendricks (1998), however, located live animals at the surface during mid-day when ambient surface conditions were overcast, wet and cool. Oreohelix elrodi is also present in the occupied talus.…”

“…Foods are unknown, but it may feed most often on plant material on rock surfaces (lichens, etc.) rather than patches of accumulated leaf and conifer needle litter , Hendricks 1998).…”