Toxolasma parvus


Jim Rathert

Unionidae (freshwater mussels) in the phylum Mollusca


Shell is small, stout, thick, elliptical and inflated. Umbo is moderately broad and low. Epidermis is light brown to greenish-brown, becomes dark brown to black with age. Inside shell beak cavity is shallow to moderately deep; pseudocardinal teeth thin, high, triangular and roughened; lateral teeth also thin but well developed, long, high and blade-like; nacre (lining) bluish-white, sometimes with salmon tinge, iridescent posteriorly.

Similar species: Purple lilliputs have larger, more rounded shells with distinctive purple nacre and are found in the southern Ozarks. Texas lilliputs, newly known in Missouri, have a satiny sheen to their shells.


Adult length: 1-2 inches.

Habitat and conservation

Large rivers with slow to no current in silt, mud, silt and sand or fine gravel; also in ponds, lakes, large reservoirs and overflow waters.


Algae and fine particles of decaying organic matter; extracts nutrients and oxygen from water drawn into the body cavity through a specialized gill called the incurrent siphon; sediment and undigested waste are expelled through the excurrent siphon.

image of Lilliput Distribuion Map
Distribution in Missouri

In appropriate habitats, fairly widespread throughout the state, in part due to its ability to adapt to lake environments (including the Lake of the Ozarks, Lake Hunnewell and Stockton Reservoir).


Uncommon. Sporadic, but more common than the other two lilliput species.

Life cycle

Males release sperm directly into water. Females downstream siphon sperm into the gill chamber, where eggs are fertilized. Eggs mature into larvae (called glochidia), which discharge into the water and attach to host fish. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.

Human connections

Mussels are excellent biological indicators of water quality because they are long-lived and relatively immobile, accumulating contaminants in water that can be scientifically analyzed.

Ecosystem connections

Mussels act as nature's “vacuum cleaners,” filtering and cleansing polluted waters. They are also an important food source for other species in the aquatic environment.