New York Natural Heritage Program
Alewife Floater
Anodonta implicata Say, 1829
Bivalves

General Description [-]
This mussel has a subelliptical shell that is elongate and posteriorly thin, but anteriorly thicker, often > 100 mm long. The beak sculpture is double-- looped, not nodulous. The periostracum is greenish, brownish, or blackish, sometimes with fine rays. Hinge teeth are absent. The nacre is pinkish to purplish, and the color is best seen on the anterior part of the shell (Strayer and Jirka 1997).

Identifying Characteristics [-]
This species can be distinguished by its toothless hinge, its pink to purple nacre, shell thickness markedly increasing anteriorally, and its double looped beak sculpture (Strayer and Jirka 1997).

Best Life Stage for Proper Identification [-]
Adult

Behavior [-]
Adults of this species are sessile with only limited movement in the substrate. Passive downstream movement may occur when they are displaced from the substrate during floods. More major dispersal occurs while glochidia are encysted on their anadromous hosts. Being ectothermic, activity levels of mussels are reduced greatly during colder months of the year.

Diet [-]
Larvae (glochidia) of this species are parasitic on the gills of Alewives (Alosa pseudoharengus). Other species of Alosa (shad) may serve as hosts as well. Adult pearly mussels are filter feeders, able to ingest a wide range of particle sizes. Algae, detritus and bacteria are all important food sources. Mussels in turn are eaten by muskrats, raccoons, fish, and birds. (Strayer and Jirka 1997).
Alewife Floater Images
click to enlarge
The Best Time to See
Little is known about the activity periods of Unionid mussels but they are presumed to be greatly reduced during cold times of the year. Freshwater mussels are most often easiest to locate during late summer when water levels are lowest. Phenology information in the table below is extrapolated from the co--occurring Alasmidonta heterodon in North Carolina (Michaelson and Neves 1995) .
J F M A M J J A S O N D
Present Active Reproducing Larvae present and active
The time of year you would expect to find Alewife Floater present (red shading), active (blue shading), reproducing (green shading) and larvae present and active (orange shading) in New York.
Similar Species
  • Creeper (Strophitus undulatus)
    Strophitis has a bluish--white nacre, and a concentric beak structure.
  • Lake Floater (Pyganodon lacustris)
    Pyganodon species are usually much larger and a have bluish--white nacre (as opposed to pink to purple) and thinner shells.
  • Giant Floater (Pyganodon grandis)
    Pyganodon species are usually much larger and have a bluish-- white nacre (as opposed to pink to purple) and thinner shells.
  • Eastern Floater (Pyganodon cataracta)
    Pyganodon species are usually much larger and have a bluish--white nacre (as opposed to pink to purple) and thinner shells.
  • Cylindrical Papershell (Anodontoides ferussacianus)
    Anodonta implicata can be distinguished from Anodontoides ferrussacianus by its double looped beak sculpture (A. ferrussacianus' beak is concentric)