The Sphaeriidae are tiny clams that live in freshwater lakes, streams, rivers, ponds, and ephemeral habitats.
Superfamily: Corbiculacea
Family: Sphaeriidae, three genera in family: Musculium, Sphaerium, and Pisidium
Common Name: Fingernail clam
Habitat: Infaunal and epifaunal in freshwater lakes, streams, rivers, ponds, ephemeral habitats
Size: Small, shell length ranges between 1 and 25 mm, with an average length less than 6 mm
Life span: Short-lived (1-3 years)
Reproductive Cycle:
· Hermaphroditic with internal fertilization.
· Ovoviviparous (i.e., brooding embryos throughout early development stages on gill).; give birth to completely developed miniature clams.
Distinguishing Characteristics of Native Corbiculacea:
Internal
· Cardinal teeth (internal dorsal shell structures that aid in shell valve articulation) present.
· Lateral teeth (internal dorsal shell structures that aid in shell valve articulation) present.
In many species of bivalves the two portions of the shell are joined together by large and often distinct teeth that aid in holding the shell pieces together.
· Gills adapted for brooding of larvae; marsupial or brood sacs present.
Whereas larvae of Dreissenidae are completely pelagic (i.e., free floating in the water column), other freshwater bivalves (e.g., Corbiculidea, Unionidae, Sphaeriidea) brood their larvae through early development stages in marsupial sacs on the gill. Shelled juveniles (arrows) of a fingernail clam, Musculium sp. (Sphaeriidae) can be seen in this scanning electron micrograph.
External
· Small, often delicate shell valves.
· Infaunal and epifaunal.
· Umbone located dorsally.
· Byssal threads absent.