 New York Metropolitan Region and New Jersey
Freshwater Mussel Identification Handbook
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Family Unionidae
Genus Alasmidonta
 Status: Of the five species in this genus known to occur in New York state,
the metro area has three: A. heterodon, A. undulata and A. varicosa. The other
two species have ranges that reach only western and central New York state.
Of the three species in this area, A. heterodon is listed as both a state and
federal endangered species in New York, New Jersey and Connecticut. It is currently known
from only a few sites in the metro area. A. varicosa has declined from its formerly widespread
status; it is listed as threatened in New York, and as endangered in New Jersey and Connecticut.
A. undulata is regarded as a species of special concern by some workers, although it is not
yet legally protected in any of the three states.
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Species Summaries
 Alasmidonta heterodon (Lea, 1830) dwarf wedgemussel
Features:
size: 45mm (up to 55mm)
beak: two concentric ridges surrounded by two to three trapezoidal ridges on the
posterior slope, beak low, rounded, and elevated slightly above the hinge line
color patterns: numerous fine color rays; periostracum yellowish-olive, green or blackish;
nacre bluish white
shape: distinctive shell shape (rhomboidal to subtriangular), anterior margin curved sharply
shell features: prominent posterior ridge, small size
teeth: reverse lateral teeth (2 in the right valve, 1 in the left- unique among NY taxa)
Status:
abundance: Rare
status: US, NY, NJ, CT: endangered; IUCN: endangered
Distribution:
N.A. distribution: New Brunswick (Canada) to North Carolina
present metro distribution: NY: a short reach of the lower Neversink River
(upper Delaware River watershed); NJ: Flatbrook, Pequest River, Paulins Kill, upper Delaware
River; CT: not present in metro area Map
other regional localities: CT: present in a few Connecticut River tributaries
historical localities: NJ: Hackensack and Passaic Rivers; CT: Connecticut River
watershed, Housatonic River watershed, South central coast watershed
Life History:
habitat: A. heterodon is found in streams, creeks and rivers, and utilizes several
hosts; it favors moderate to fast flowing water on substrates of cobble, fine gravel, or
fine silt and sand, and has also been found to utilize the root systems of trees at
the water's edge Habitat Photo
hosts: Cottus bairdi (Girard, 1850) mottled sculpin; Cottus cognatus (Richardson, 1836)
slimy sculpin; Etheostoma nigrum (Rafinesque, 1820) johnny darter; Etheostoma olmstedi
(Storer, 1842) tesselated darter; Salmo salar (Linnaeus 1758) Atlantic salmon
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Key Features Refresher
Anterior and Posterior
Beak and Beak Sculpture Color Ray
Hinge Teeth Length, Width, Height, Profile, Silhouette
Growth Line Posterior Ridge and Slope
Shell Shape
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Plates
A. heterodon |
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left view
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right view
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dorsal view;
beak and posterior ridge
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profile view;
rhomboidal to trapezoidal shape
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nacre bluish-white
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reverse lateral teeth:
two teeth on the right valve,
one on the left
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beak sculpture: two concentric ridges
surrounded by several trapezoidal
rings on the posterior ridge
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beak sculpture, detail
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 Alasmidonta undulata (Say, 1817) triangle floater
Features:
size: 80mm
beak: heavy, coarse, uneven, with concentric sculpture; umbos extend above hinge line
color patterns: bright green color rays; nacre may be white, salmon, pink or red
shape: triangular ovate, anterior rounded, ventral margin broadly rounded
shell features: smooth, shiny yellow-brown periostracum, shell thickness decreases
markedly from anterior to posterior
teeth: pseudocardinals strong, one in left valve, two in right; laterals vestigial; well-developed
interdental tooth in the left valve
Status:
abundance: common
status: US, NY, CT: not legally protected; NJ: threatened; declining in parts of its N.A.
range and considered by some observers to be a species of special concern in the metro area
Distribution:
N.A. distribution: Nova Scotia (Canada) west to the St. Lawrence River drainage,
and south to Florida
present metro distribution: NY: upper Hudson River and upper Delaware River
watersheds; NJ: Hackensack River; Lamington/Raritan River, Stony Brook, Ramapo River
(lower Hudson River watershed), Lubbers Run/Musconetcong River, and Paulins Kill River
(upper Delaware River watershed). Pequest River, Hayne's Creek; CT: Connecticut River
and Thames River watersheds Map
other regional localities: CT: all Connecticut watersheds except southwest coast
and Hudson River watersheds
historical localities: CT: Housatonic River watershed
Life History:
habitat: large creeks and small rivers, sometimes lakes; found in both slow and
fast-moving water; substrate may vary from silt/sand in slow-moving water to gravel/sand
in fast water Habitat Photo
hosts: Campostoma anomalum (Rafinesque, 1820) central stoneroller; Cottus
cognatus (Richardson, 1836) slimy sculpin; Etheostama flobellare (Rafinesque, 1819) fantail
darter; Hypentelium nigricans (Lesueur, 1817) northern hogsucker; Lepomis gibbosus
(Linnaeus, 1758) pumpkinseed; Luxilus cornutus (Mitchill, 1817) common shiner;
Micropterus salmoides (Lacepede, 1802) largemouth bass; Notropis rubellus (Agassiz, 1850)
rosyface shiner; Rhinichthys atratulus (Hermann, 1804) blacknose dace;
Rhinichthys cataractae (Valenciennes, 1842) longnose dace; Semotilus corporalis
(Mitchill, 1817)
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Key Features Refresher
Anterior and Posterior
Beak and Beak Sculpture Color Ray
Hinge Teeth Length, Width, Height, Profile, Silhouette
Growth Line Posterior Ridge and Slope
Shell Shape
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Plates
A. undulata
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left view
periostracum shiny, color rays bright
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right view
beak heavy
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dorsal view
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shell thickness decreases markedly
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beak sculpture heavy, concentric
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pseudocardinals strong,
laterals vestigial
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 Alasmidonta varicosa (Lamarck, 1819) brook floater
Features:
size: 70mm
beak: coarse, shape variable, projects slightly above hinge line
color patterns: dark green, continuous color rays; bright orange foot; nacre bluish-
white with salmon in the beak cavity
shape: sub-trapezoidal to sub-ovate; anterior shell margin abruptly curved; ventral margin
slightly concave
shell features: inflated, rounded posterior ridge; fine corrugations on posterior slope
teeth: thin, lamellar pseudocardinals with smooth surfaces, one each in left and right
valve; laterals vestigial to absent
Status:
abundance: rare
status: US, NY, NJ, CT: endangered
Distribution:
N.A. distribution: New Brunswick (Canada) to South Carolina
present metro distribution: NY: Neversink River (upper Delaware River watershed),
Shawangunk Kill (upper Hudson River watershed); NJ: north branch of the Raritan River
and Stony Brook Creek (lower Hudson River watershed), Musconetcong River (upper
Delaware River watershed), Lamington River, Flatbrook, Paulins Kill; CT: not present in the
metro area Map
other regional localities: NY: upper Susquehanna River watershed; CT: Thames and
Connecticut River watersheds
historical localities: NY: Housatonic River watershed, Lower Hudson River watershed,
Oswego River watershed; NJ: Passaic River (lower Hudson River watershed); CT: lower
Connecticut River watershed, Housatonic River watershed
Life History:
habitat: confined to creeks and small rivers, typically in fast water on a substrate
of stable gravel or sandy shoals Habitat Photo
hosts: Cottus cognatus (Richardson, 1836) slimy sculpin; Lepomis gibbosus (Linnaeus,
1758) pumpkinseed; Notemigonus crysoleucas (Mitchill, 1814) golden shiner; Noturus
insignis (Richardson, 1836) margined madtom; Perca flavescens (Mitchill, 1814)
yellow perch; Rhinichthys atratulus (Hermann, 1804) blacknose dace; Rhinichthys
cataractae (Valenciennes, 1842) longnose dace
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Key Features Refresher
Anterior and Posterior
Beak and Beak Sculpture Color Ray
Hinge Teeth Length, Width, Height, Profile, Silhouette
Growth Line Posterior Ridge and Slope
Shell Shape
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Plates
A. varicosa
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left view
shell sub-trapezoidal to sub-ovate
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right view
shell dark green with strong color rays
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dorsal view
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profile view;
enlarged posterior ridge
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nacre bluish-white;
note areas of discoloration
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laterals vestigial or absent
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beak sculpture coarse, shape variable;
fine corrugations on posterior slope
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pseudocardinals thin, lamellar
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