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Montana Field Guide

Montana Field Guides

Lake Amnicola - Amnicola sp. 2

Native Species

Global Rank: G1
State Rank: SNR
(see State Rank Reason below)

Agency Status

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State Rank Reason (see State Rank above)
Currently only known from 1 lake in NW Montana and potentially an introduced population, but further inventories need to be conducted to confirm it's true rarity or just lack of surveys.
General Description
This is a small, tan-brown colored, operulate snail in the Hydrobiid family; it was formerly called the Washington duskysnail, now Lake Amnicola is the accepted nomenclature despite not being formerly described. Shell reaches a height of 5.0mm, is ovate-conic, has well rounded whorls (4-5 in adult), and a small umbilicus (Frest and Johannes, 1995).

Diagnostic Characteristics
Shell similar to that of Amnicola limosa (see Hershler & Thompson, 1988); height to. 5.0
mm: ovate-conic, well-rounded whorls; comparatively thin; 4-5 whorls in adult; small umbilicus.

Range Comments
Currently documented from only four lake sites; one in western Washington, two in northeastern Washington and one in northwest Montana (Frest and Johannes, 1995, Johannes, 2010 and K. Jurist personal communication, 1995). But, recent evidence points to a potential introduction into Georgetown Lake (Edward Johannes 2012, pers comm.).


Freshwater. Lakes and lentic ecological systems.

Food Habits
In addition to being a detritivore the species also grazes along the stems and leaves of aquatic plants eating small organisms clinging to this material (Frest and Johannes, 1995).

The species is a "limnophile" occurring in kettle lakes among aquatic vegetation beds, but absent from dense aquatic vegetation areas (Frest and Johannes, 1995). The species is found on soft oxygen rich substrate at a depth of approximately 2-6 feet (Frest and Johannes, 1995). lt is apparently a limnophile, unlike Amnicola limosa, which occurs in streams as well.

Species is quite rare in WA and MT, but may be more common in suitable habitats of northern ID. We need more targeted lake surveys; this lack of attention may be limiting the knowledge of this species true distribution.

Threats or Limiting Factors
Many of the kettle lakes in the area of occurrence have heavily developed shorelines, including housing with inadequate provisions for sewage and runoff management. Siltation in many of these formerly cobble-bottom oligotrophic environments is also a problem, exacerbated by logging, grazing, and residential development; the great majority of NW MT kettle lakes have these problems (Frest and Johannes 1995).

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Citation for data on this website:
Lake Amnicola — Amnicola sp. 2.  Montana Field Guide.  .  Retrieved on , from