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Home/Species/ Fat Threeridge

Amblema neislerii

(I. Lea, 1858)

Fat Threeridge

G1Critically Imperiled Found in 1 roadless area NatureServe Explorer →
G1Critically ImperiledGlobal Rank
Critically endangeredIUCN
Very high - highThreat Impact
Fat threeridge (mussel) (Amblema neislerii). Photo by U.S. Fish & Wildlife Service, Public Domain (U.S. Government Work), via ECOS.
U.S. Fish & Wildlife Service, https://www.usa.gov/government-works
Identity
Unique IDELEMENT_GLOBAL.2.107426
Element CodeIMBIV03010
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryInvertebrate Animal
IUCNCritically endangered
Endemicendemic to a single nation
KingdomAnimalia
PhylumMollusca
ClassBivalvia
OrderUnionoida
FamilyUnionidae
GenusAmblema
Other Common Names
fat threeridge (EN) Fat threeridge (mussel) (EN)
Concept Reference
Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-05-06
Change Date2006-05-01
Edition Date2025-05-06
Edition AuthorsJackson, D. R. (2014); Cordeiro, J. (2006); rev. T. Cornelisse (2025)
Threat ImpactVery high - high
Range Extent1000-5000 square km (about 400-2000 square miles)
Number of Occurrences6 - 20
Rank Reasons
This species has a restricted range and a low number of known occurrences that have declined over time due to many ongoing threats.
Range Extent Comments
This species is endemic to the Apalachicola River system, where it is known from the lower Flint River in Georgia, and the Apalachicola and lower Chipola rivers in Florida, USA (Clench and Turner 1956; Williams and Butler 1994; USFWS 2021).
Occurrences Comments
This species is known from 6 river units that are equivalent to subpopulations (USFWS 2021; InvertEBase 2025; RARECAT 2025).
Threat Impact Comments
This species is threatened by sedimentation, nutrient, and chemical pollution from land conversion activities, including development and agriculture, dams and water diversions that change hydrological conditions and prevent habitat connectivity and recolonization, invasive species, and habitat alteration due to climate change, including increased droughts and floods, and sea level rise (USFWS 2021).
Ecology & Habitat

Description

See Clench and Turner (1956) for full description. Large, subquadrate, inflated, solid, and heavy shelled mussel. Older, larger individuals are so inflated that their width approximates their height. The umbos are in the anterior quarter of the shell. The dark brown to black shell is strongly sculptured with seven to eight prominent horizontal parallel ridges. There are two subequal pseudocardinal teeth in the left valve and one large one one small tooth in the right valve. Nacre is bluish white to light purplish and very iridescent (Butler and Alam, 1999).

Diagnostic Characteristics

Subquadrate, very inflated, heavy shelled, 7-9 prominent horizontal parallel ridges or corrugations, nearly black.

Habitat

This species is found in rivers with moderate to high flow with stable, fine substrates (USFWS 2021).
Other Nations (1)
United StatesN1
ProvinceRankNative
FloridaS1Yes
GeorgiaS1Yes
Threat Assessments
ThreatScopeSeverityTiming
1 - Residential & commercial developmentRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
1.1 - Housing & urban areasRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
2 - Agriculture & aquacultureLarge - restrictedModerate or 11-30% pop. declineHigh (continuing)
2.1 - Annual & perennial non-timber cropsLarge - restrictedModerate or 11-30% pop. declineHigh (continuing)
7 - Natural system modificationsSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
7.2 - Dams & water management/useSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesRestricted (11-30%)Slight or 1-10% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesRestricted (11-30%)Slight or 1-10% pop. declineHigh (continuing)
9 - PollutionLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
9.1 - Domestic & urban waste waterRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
9.2 - Industrial & military effluentsSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
9.3 - Agricultural & forestry effluentsLarge - restrictedSerious or 31-70% pop. declineHigh (continuing)
11 - Climate change & severe weatherPervasive (71-100%)Serious - moderateHigh (continuing)
11.1 - Habitat shifting & alterationPervasive (71-100%)Serious - moderateHigh (continuing)

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Roadless Areas (1)
Florida (1)
AreaForestAcres
SavannahApalachicola National Forest1,927
References (44)
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