Paper Pondshell (Paper Floater)

Utterbackia imbecillis


paper pondshell
Jim Rathert

Unionidae (freshwater mussels) in the phylum Mollusca


Very thin, elongate shell; oblong and inflated in adults. Umbo not raised above the very flat hinge line. Epidermis is shiny, yellow to green with faint yellow to green rays; young are beautiful bright green, with thin glossy shells. Inside shell beak cavity shallow to absent; teeth absent; nacre (lining) iridescent white to bluish-white.

Similar species: Small giant floaters are distinguished by umbo distinctly raised above the hinge line.


Adult length: 1-4 inches.

Habitat and conservation

Quiet water in ponds, lakes, reservoirs, sloughs and streams. Found in rivers as large as the Mississippi and as small as the Maries. In rivers, it favors quiet backwaters and eddies in silt or a mix of silt and fine sand.


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 Paper Pondshell Paper Floater Distribution Map
Distribution in Missouri

Statewide but sporadic; sometimes locally abundant.


Fairly common, although degrading water quality and watershed destabilization interfere with the survival of this and all freshwater mussels.

Life cycle

As with most mussels, males release sperm into water, and females downstream siphon sperm into the gill chamber, where eggs are fertilized. Eggs mature into larvae and discharge into the water and attach to host fish. The growing mussel later breaks away and floats to the stream bottom, and the cycle repeats. This species, unlike most other freshwater mussels, is hermaphrodic: An individual can produce both eggs and sperm, and can also fertilize itself.

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.