Trinity Bristle Snail

The Trinity bristle snail (Monadeniasetosa ) (fig. 3) is a terrestrial snail, living in the riparian zone along several small, primary streams in the Trinity River drainage in Trinity County (Roth and Eng 1980). Adults of this nocturnal species are most commonly found among leaf litter on the forest floor, although they have been observed several feet up in the branches of deciduous trees.^[3] Very young snails are apparently dependent upon standing dead trees, spending the first several months of their existence living beneath the loose bark. Trinity bristle snails are active during the moist months of the year, feeding on fungi and decomposing leaves.

Figure 3.
The Trinity bristle snail (Monadenia  setosa ).

The Trinity bristle snail occurs only in the presence of a hardwood understory including bigleaf maple (Acer macrophyllum ), dogwood (Cornus sp.), and California hazel (Coryluscornuta var. californica ). In the lower stream reaches, white alder (Alnus rhombifolia ), California black oak (Quercus kellogii ) and tanbark-oak (Lithocarpus densiflora ) are sometimes interspersed with the above species. The decaying leaf litter from these trees apparently constitutes a major food source for the snail (Roth and Eng 1980). On the dryer upper slopes M . setosa is replaced by its cogener M . churchi ; it is also absent from lightly shaded areas of exposed hillsides.

The Trinity bristle snail is restricted to sparsely populated, mountainous Trinity County. Much of its habitat is on national forest land. Because of its restricted habitat and very limited range, the California Fish and Game Commission has designated it a Rare species under California law. Threats to this species are logging activities which would encroach on the riparian zone. Fires, road construction, erosion, and removal of standing trees utilized by the juvenile snails would all have substantial deleterious effects on the snail's habitat. Other potential threats come from gold-mining operations and the development of small hydroelectric projects. The USDA Forest Service has responded to the presence of this rare snail and has developed an interim management plan for it (Armijó 1979).