Genus Alasmidonta main content.

Genus Alasmidonta

Family Unionidae

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.

Species Summaries

Alasmidonta heterodon In and Out

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
conservation challenges: sites should be sought in the lower Delaware watershed in New Jersey. If found, living specimens of this species should never be collected; in addition, dead shells of all federally endangered species cannot be collected without a permit.

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

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

alasmidontahetmap

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

Plates

A. heterodon

Left View
left view
Right View
right view
Dorsal View
dorsal view;beak and posterior ridge 
Profile View
profile view;rhomboidal to trapezoidal shape
 
Nacre
nacre bluish-white
Reverse lateral teeth
reverse lateral teeth: two teeth on the right valve,one on the left
Beak Sculpture
beak sculpture: two concentric ridges surrounded by several trapezoidal rings on the posterior ridge
Beak Sculpture Detail
beak sculpture, detail
 

 

Summaries

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
conservation challenges: Legal protection for this species in New Jersey is critical. Other sites in the lower Delaware watershed should be sought.

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
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

brookfloatersmall

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

Plates

A. varicosa

Left View
left viewshell sub-trapezoidal to sub-ovate
Right View
right viewshell dark green with strong color rays
Dorsal View
Dorsal View
Profile View
profile view;enlarged posterior ridge
Nacre
nacre bluish-white;note areas of discoloration
Laterals
laterals vestigial or absent
A closed clam
beak sculpture coarse, shape variable, fine corrugations on posterior slope
Pseudocardinals
pseudocardinals thin, lamellar
 

 

Alasmidonta undulata full

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
conservation challenges: this species should be closely monitored; its two sister species are already endangered or threatened

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
other regional localities: CT: all Connecticut watersheds except southwest coast and Hudson River watersheds
historical localities: CT: Housatonic River watershed

trianglefloatersmall

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)

Plates

A. undulata

The outer and inner shells of the dwarf wedgemussel (Alasmidonta heterodon)
left viewperiostracum shiny, color rays bright
 
Two halves, one showing the interior, one the exterior of the shell of an Alasmidonta undulata, the freshwater triangular floater mussel.
right viewbeak heavy
Dorsal View
dorsal view
 
Shell Thickness
shell thickness decreases markedly
 
Beak Sculpture
beak sculpture heavy, concentric
Pseudocardinals
pseudocardinals strong,laterals vestigial