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Platynaias subviridis

(Conrad, 1835)

Green Floater

G2Imperiled (G2G3) NatureServe Explorer →
G2ImperiledGlobal Rank
Least concernIUCN
Very high - highThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.107377
Element CodeIMBIV22060
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryInvertebrate Animal
IUCNLeast concern
Endemicendemic to a single nation
KingdomAnimalia
PhylumMollusca
ClassBivalvia
OrderUnionoida
FamilyUnionidae
GenusPlatynaias
Synonyms
Lasmigona subviridis(Conrad, 1835)
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.
Taxonomic Comments
Transferred from the genus Lasmigona to Platynaias; this treatment is accepted by both MolluscaBase (2026) and FMCS (2025). The generic transfer is based on genetic data from several papers that placed compresss, decorata, and subviridis in the same clade (Whelan et al. 2023, Bogan and Smith 2025; Perkins et al. 2025; Campbell and Lydeard 2026).
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2024-01-03
Change Date2024-01-03
Edition Date2024-01-02
Edition AuthorsStevenson, P. (1992); rev. K. Motivans (1998); rev. J.Cordeiro (2011); rev. T. Cornelisse (2024)
Threat ImpactVery high - high
Range Extent20,000-200,000 square km (about 8000-80,000 square miles)
Number of Occurrences21 - 300
Rank Reasons
This species has a moderate range but due to long and short-term population declines and many ongoing threats, there are a limited number of viable occurrences.
Range Extent Comments
This species occurs in Maryland, New Jersey, New York, North Carolina, Pennsylvania, Tennessee, Virginia, and West Virginia, USA (USFWS 2021).
Occurrences Comments
This species is known from 94 occurrences, using records from 1999-2019, but only 30 of those occurrences are in good condition and likely to persist (USFWS 2021).
Threat Impact Comments
This species is threatened by dams and water withdraws, invasive species, sedimentation, pollution that impacts water quality, and the habitat changes due to climate change (USFWS 2022). (USFWS 2021).
Ecology & Habitat

Description

Shell subovate to ovate, narrower in front and higher behind. Shell unsculptured. Anterior margin rounded. Ventral margin slightly convex to centrally flattened. Posterior margin sharply rounded, subacute, or somewhat biangulate below and obliquely flattened above, and dorsal margin broadly sinuate to gently convex throughout. Dorsal margin sometimes forms a winglike angle with posterior margin. Beaks, located in the anterior third of the shell, project little above hinge line (Clarke, 1985). Posterior ridge rounded, sometimes obscurely double and subangular (Clarke, 1985). Shell not compressed nor inflated. Periostracum pale yellowish or brownish with numerous narrow or wide green and blackish rays. Rays are particularly conspicuous in juveniles (Clarke, 1985). Shell is smooth, with slightly raised, darkened annulli. Teeth well-developed but small and delicate. Possesses lammellar or serrate pseudocardinal teeth oriented nearly parallel to hinge line. Left valve has 2 pseudocardinals and right valve has one. Lateral teeth narrow, sharp and of moderate length. Two lateral teeth in the left valve and one in the right valve; sometimes the lateral teeth are incomplete or indistinct (Clarke, 1985). A rudimentary interdental projection, often obscure, exists in the left valve. Shell moderately thin, with nacre white anteriorly, and posteriorly iridescent and bluish or greenish white. Nacre with blotches of dull greenish or yellowish color. From Clarke (1985):" Mantle yellowish white at the marginal muscle band, near the adductor muscles and over the diaphragm; translucent centrally and above the diaphragm. Foot orange, visceral mass yellowish white, and adductor muscles pale yellowish brown. ... Mantle with a narrow band of dark brown pigment along the margin only near the incurrent and anal openings... Outer demibranch pale orange... Inner demibranch also pale orange...". Ortmann (1912) described the species as being hermaphroditic with female gill structure occurring in the outer demibranchs of all specimens. An extensive description and illustrations of the species are available in Clarke (1985).

Habitat

This species is found in small streams to rivers with low to moderate gradients in pools and eddies with gravelly and sandy bottoms (Clarke 1985; Strayer and Jirka 1997; USFWS 2021).

Reproduction

This species is a long-term brooder and that juveniles can metamorphose without a host within the marsupia of the adult female (Barfield and Watters 1998; Lellis and King 1998).
Other Nations (1)
United StatesN2
ProvinceRankNative
GeorgiaSXYes
District of ColumbiaSHYes
New JerseyS1Yes
MarylandS1Yes
New YorkS2Yes
VirginiaS2Yes
North CarolinaS2Yes
AlabamaSXYes
West VirginiaS2Yes
PennsylvaniaS2Yes
TennesseeS2Yes
Threat Assessments
ThreatScopeSeverityTiming
7 - Natural system modificationsLarge - restrictedSerious - moderateHigh (continuing)
7.2 - Dams & water management/useLarge - restrictedSerious - moderateHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
8.1.2 - Named speciesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
9 - PollutionLarge (31-70%)Serious - moderateHigh (continuing)
9.2 - Industrial & military effluentsRestricted (11-30%)Serious - moderateHigh (continuing)
9.3 - Agricultural & forestry effluentsLarge - restrictedSerious - moderateHigh (continuing)
9.3.2 - Soil erosion, sedimentationLarge - restrictedSerious - moderateHigh (continuing)
11 - Climate change & severe weatherLarge (31-70%)Serious - moderateHigh (continuing)
11.1 - Habitat shifting & alterationLarge (31-70%)Serious - moderateHigh (continuing)

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