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Brachyanodon californiensis

(I. Lea, 1852)

California Floater

G3Vulnerable NatureServe Explorer →
G3VulnerableGlobal Rank
Least concernIUCN
HighThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.1066185
Element CodeIMBIV04220
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryInvertebrate Animal
IUCNLeast concern
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomAnimalia
PhylumMollusca
ClassBivalvia
OrderUnionoida
FamilyUnionidae
GenusBrachyanodon
Synonyms
Anodonta californiensisI. Lea, 1852Anodonta dejectaLewis, 1875
Other Common Names
Anodote de Californie (FR)
Concept Reference
Williams, J. D., A. E. Bogan, R. S. Butler, K. S. Cummings, J. T. Garner, J. L. Harris, N. A. Johnson, and G. T. Watters. 2017. A revised list of the freshwater mussels (Mollusca: Bivalvia: Unionida) of the United States and Canada. Freshwater Mollusk Biology and Conservation 20:33-58.
Taxonomic Comments
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. Anodonta dejecta was recognized by Turgeon et al. (1998), Graf and Cummings (2007), and Cummings and Graf (2010). This species is treated as a synonym of A. californiensis by Bequaert and Miller (1973) and the Arizona Game and Fish Department (2017) and is therefore placed in synonymy of A. californiensis by Williams et al. (2017).
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2026-02-12
Change Date2003-12-15
Edition Date2026-02-12
Edition AuthorsCordeiro, J. (2007); rev. T. Cornelisse (2026)
Threat ImpactHigh
Range Extent200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Number of Occurrences21 - 300
Rank Reasons
This species was once thought to have been widespread in the Pacific Drainage from British Columbia into Mexico, but there is considerable taxonomic confusion as to the placement of the western North American Anodonta species. The current range however is patchy, and it has been lost from many parts of its former range due to many ongoing threats.
Range Extent Comments
This species occurs in British Columbia, Canada, in the western United States from Washington to Wyoming, south to Arizona and west to California (Frest and Johannes 1995; Hovingh 2004; Mock et al. 2005; RARECAT 2025; NatureServe 2026). There is still some taxonomic uncertainty in this genus and so some records may be deemed that of congeners with additional taxonomic resolution (Williams et al. 2017; O'Brien et al. 2019).
Occurrences Comments
This species is found in at least approximately 80 occurrences using a 10 km separation distance and records from 1994-2026 (Frest and Johannes 2000; Mock et al. 2004; Hovingh 2004; Nedeau et al. 2005; Cvancara 2005; WNHP 2008; Howard 2010; BCCDC 2013; Nevada Natural Heritage Program 2018; Arizona Heritage Data Management System 2021; RARECAT 2025; NatureServe 2026).
Threat Impact Comments
This species is threatened by sedimentation, nutrient, and chemical pollution from land conversion activities, including development, agriculture and industrial activities, dams and water diversions that change hydrological conditions and prevent habitat connectivity and recolonization, habitat alteration due to climate change, including increased water temperatures and drought, as well as predation by non-native fish and introduced crayfish, and a possible link to reduced populations of native fish that serve as larval hosts (WNHP 2008; BCCDC 2013; Nevada Natural Heritage Program 2018; Arizona Heritage Data Management System 2021).
Ecology & Habitat

Habitat

This is a low elevation species that is found in both lakes and lake-like stream environments (Frest and Johannes 1995).
Other Nations (1)
United StatesN3
ProvinceRankNative
WyomingS2Yes
OregonS2Yes
NevadaS1Yes
IdahoS3Yes
UtahS2Yes
CaliforniaS2Yes
ArizonaS1Yes
WashingtonS2Yes
Threat Assessments
ThreatScopeSeverityTiming
7 - Natural system modificationsRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
7.2 - Dams & water management/useRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
9 - PollutionRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
9.2 - Industrial & military effluentsRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
9.3 - Agricultural & forestry effluentsRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
11 - Climate change & severe weatherLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
11.1 - Habitat shifting & alterationLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)

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References (62)
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