Anodonta kennerlyi

Western Floater

FWS Focus

Overview

Characteristics
Overview

In western North America there are possibly five species of mussels commonly known as floaters. This page details the western floater (Anodonta kennerlyi). It should be noted; however, that distinguishing between species of Anodonta in the west is problematic due in part to high variability in shape between individuals. As such, the legitimacy of the speciation for floaters in western North America remains unresolved. Genetic analysis has indicated that the western floater and Oregon floater (Anodonta oregonensis) share a common ancestry with shared physical features and can be considered a clade (a related group). Information in this page is specific to the western floater when available.

The western floater is known to occur in Oregon, Washington, Alaska, British Columbia, Alberta, and northern Saskatchewan. Western floaters can be found in different water types but most commonly in still waters with silty and sandy bottoms. The shell is thin and lightweight, and the species grows to about five to seven inches long. 

Scientific Name

Anodonta kennerlyi
Common Name
western floater
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Physical Characteristics

Characteristics
Physical Characteristics

Deliberate lateral and vertical movements by mussels does occur, but the movement is usually limited.  Because mussels don’t have vision, lateral movements can seem random and be multidirectional.  In some locations where ice can occur attached to the substrate (anchor ice), mussels may move vertically, burying into the substrate during the winter, and moving to the surface in the spring.  Vertical movements during the spring to early fall may also be related to reproduction or a response to disturbance by other animals, predators or people.  Lateral mussel displacement due to high flows or dislodgement due to predators or human activity also likely occurs.  Mussel larvae have a parasitic phase where they attach to a host fish and can be moved by that host within the aquatic system.

Color & Pattern
Size & Shape

The western floater is elliptical in shape with a length to height ratio near or exceeding 2:1 and grows to about seven inches long.  Shells are thin and lightweight with a beak that rarely projects above the hinge line. The exterior color ranges from yellowish, to brown, to black. The interior color of the valve is typically white or bluish white and can sometimes be pinkish toward the middle. Holding true to “Anodonta,” which is Latin for “without teeth”, an Oregon floater lacks any sort of tooth within its valves.

Characteristic category

Behavior

Characteristics
Behavior

Freshwater mussels are sedentary, spending their entire lives near where they settled. They can use their foot to move laterally across sediments (usually short distances) or vertically within the sediments. Mussel movements may be related to reproduction or a response to physical disturbance and environmental changes such as water temperature, stream flows, or scouring of the stream bed. Mussel displacement due to high flows or dislodgement due to predators or human activity also likely occurs. The main mode of mussel dispersal comes through a stage of development when larvae (glochidia) parasitize a host fish and move with the host within the aquatic system.

Characteristic category

Habitat

Characteristics
Habitat

Western floaters are found in ponds, lakes, and reservoirs but can also occur in slow-flowing stream reaches. They can be found in silty bottoms and sandbars at stream confluences. 

River or Stream
Lake
Characteristic category

Food

Characteristics
Food

Like all freshwater mussels, western floaters are filter feeders that siphon suspended particles from the water column. They may consume plankton, bacteria, dissolved organic matter, or algae. This filtering provides an important water quality service by reducing turbidity and controlling nutrient levels, especially where there are dense mussel beds. Particles not used by the mussel are often re-formed and expelled as larger particles that are in turn used as food by other aquatic life.

Characteristic category

Life Cycle

Characteristics
Life Cycle

Anodonta species become sexually mature at about four to five years of age and can live to about 15 years. Relative to other western mussel species, they are considered short lived and fast growing. Male mussels release sperm into the water and a female takes it in through her incurrent siphon to fertilize eggs. Fertilized eggs migrate within the mussel to a special portion of the gill known as the marsupium. The eggs develop into larvae called glochidia and are released by the female in the spring through early summer. Once released, the glochidia, which look like very tiny mussels, attach to a host fish’s gills where they become encysted and remain for weeks to months until they detach and settle to the substrate.  Mussel species are often specific regarding what species of fish they use as hosts. The western floater is known to use prickly sculpin (Cottus asper), three-spined stickleback (Gasterosteus aculeatus), speckled dace (Rhinichthys osculus), and some species of salmonids for hosts. Anodonta glochidia in the west have been found on fish from the fall through the spring. Timing of reproductive events is affected by habitat, water temperature and the individual species.

Characteristic category

Similar Species

Characteristics
Similar Species

The western floater and Oregon floater (A. oregonensis) can be considered to be in the same taxonomic clade.

Geography

Characteristics
Range

The western floater is known to occur in Oregon, Washington, Alaska, British Columbia, Alberta, and northern Saskatchewan.