Brachyanodon nuttallianus

Brachyanodon, formerly a subgenus of Anodonta, is now recognized as a distinct genus following Campbell and Lydeard (2025). Brachyanodon needs review to determine what are species-level clades.

There remains taxonomic confusion surrounding this species complex. Williams et al. (2017) retain Anodonta californiensis, A. kennerlyi, A. nuttalliana, and A. oregonensis based on their phylogenetic affinity to Eurasian Anodonta (Mock et al. 2004; Zanatta et al. 2007; Chong et al. 2008). O'Brien et al. (2019) supports the distinctiveness of A. nuttalliana and A. californiensis.

Documented long- and short-term declines in A. nuttalliana and other western Anodonta species since last review in 2009. Low genetic diversity with hydrologic separation between populations. Distribution, along with species designation, is poorly understood as recent molecular work has brought some resolution to taxonomy and many historical records may be composed of more than one western Anodonta species. It is believed to occur in California, Oregon, Washington, and across southern British Columbia (north to 52 degrees N latitude) except Vancouver Island, possibly east to Utah (where it may be extirpated) with Idaho records believed to be A. kennerlyi. British Columbia records for A. californiensis are now believed to be applicable to this species. A proper conservation assessment requires further taxonomic study clarifying the placement of western Anodonta species, all of which are largely in decline with local extirpations and range-wide reductions.

This Range Extent analysis only includes occurrences of the putative A. nuttalliana species concept by Chong et al. (2008) and excludes those of A. californiensis, a closely related species in the same clade (Mock et al. 2010, Chong et al. 2008). Reported occurrences are not always in agreement: Blevins et al. (2017) included British Columbia, Canada; Arizona, California, Idaho, Nevada, Oregon, Utah, Washington, Wyoming, USA; Chihuahua, Sonora, Mexico that provided a Range Extent of 2,086,110 square km. Mock (2010) and Nedeau et al. (2005) included California, Oregon, Washington, southern British Columbia; east to Utah (Burch 1975); Idaho records (Henderson, 1924; 1936) records believed to be Anodonta kennerlyi. Wyoming records were identified as A. californiensis and proposals to find extant and additional populations in the Bear River drainage using eDNA and visual surveys are expected to occur for the next couple years (L. Tronstad pers. comm. 2018). Preliminary analysis (K. Mock, Utah State University, pers. comm.) indicates Utah Anodonta are distinct from A. oregonensis of the Pacific northwest and should tentatively be assigned to A. californiensis pending future taxonomic work. Clarke (1981) cites distribution as the Fraser and Columbia River systems in southern British Columbia (absent from Vancouver Island) and south to central California.
There are reports of A. nuttalliana from Mexico; however, all of the records from Mexico available on MUSSELp Database (Graf and Kummings 2018), are presently identified as other Anodonta species (mostly A. impura) on database websites of the respective institutions where they are deposited (Field Museum of Natural History, Museum of Comparative Zoology, US National Museum, Delaware Museum of Natural History,The Academy of Natural Sciences Pennsylvania). Additionally, no other occurrences available from these institutional database websites listed Mexico as a locality for specimens identified as A. nuttalliana. This will likely remain uncertain until taxonomy has better resolution and sufficient field surveys accurately document western Anodonta species.

Number of Occurrences for this Anodonta nuttalliana review did not include records of A. californiensis, a closely related species in the same clade (Mock et al. 2010, Chong et al. 2008). Historical records with uncertain identifications, sympatry, and morphological inconsistencies between species further confound characterization of its true distribution. Currently it is believed to occur in California, Oregon, Washington, southern British Columbia, Arizona, Utah, and Nevada (Mock et al. 2004, 2010, Nedeau et al. 2005, Burch 1975) with some Idaho records (Henderson 1924; 1936) records believed to be Anodonta kennerlyi.
There are reports of A. nuttalliana from Mexico; however, all of the records from Mexico available on MUSSELp Database (Graf and Kummings 2018), are presently identified as other Anodonta species (mostly A. impura) on the respective institutional database websites where they are deposited (Field Museum of Natural History, Museum of Comparative Zoology, US National Museum, Delaware Museum of Natural History,The Academy of Natural Sciences Pennsylvania). Additionally, no other occurrences available from these institutional database websites listed Mexico as locality for specimens identified as A. nuttalliana.
Preliminary analysis (K. Mock, Utah State University, pers. comm.) indicates Utah Anodonta should tentatively be assigned to Anodonta californiensis. Clarke (1981) cites distribution as the Fraser and Columbia River systems in southern British Columbia (absent from Vancouver Island) and south to central California. In Canada, it is somewhat common in British Columbia but little concise locality information is available (Metcalfe-Smith and Cudmore-Vokey 2004), however it is now believed records of what was formerly attributed to Anodonta californiensis in British Columbia is now considered Anodonta nuttalliana (BC CDC, pers. comm. 2009). In Oregon, several populations of Anodonta were recently confirmed in the Middle Fork John Day River and the lower main stem of the Umatilla River, but due to the taxonomic confusion surrounding the western Anodonta, identification to species level was not attempted (Brim Box et al. 2003; 2006), although preliminary evidence indicates the John Day River population includes A. californiensis/nuttalliana clade and the Umatilla River population include both A. oregonensis/kennerlyi and A. californiensis/nuttalliana clades in sympatry (K. Mock, Utah State University, pers. comm. 2007). Specimens have also been confirmed in the Upper Quinn and Middle Owyhee drainages in Nevada/Oregon (K. Mock, Utah State University, pers. comm. 2007). Museum specimens (UMMZ) exist for California (San Juaquin River in San Juaquin Co., Coyote Creek in San Jose Co., San Juan Tequesquito Creek in San Benito Co., Clear Lake in Lake Co., Sacramento River in Sacramento Co., North Fork Pit River in Modoc Co.), Utah (Salt Lake City canal, Warm Spring Lake, and Jordan River in Salt Lake Co., Utah Lake in Utah Co., Willow Springs in Tooele Co., Sevier River in Millard Co.), Oregon (Klamath Lake in Klamath Co.), Nevada (Humboldt River in Elko Co., Pyramid Lake in Washoe Co.), and British Columbia (Sumas and Harrison Lakes).

Threats were documented in literature.