FWS Focus

Overview

Characteristics
Overview

The Tennessee and Cumberland River basins historically contained the greatest diversity of freshwater mussels anywhere in the world.  Species specific to this area are referred to as “Cumberlandian” (Ortmann 1924).  The finerayed pigtoe is a Cumberlandian species restricted to the middle and upper Tennessee River system and has always been considered rare (Simpson 1914).  It was placed on the federal threatened and endangered species list in 1976 as endangered. 

There are currently five known populations of finerayed pigtoe – one in the North Fork Holston River in Virginia, one each in the Clinch and Powell rivers, both crossing the Virginia-Tennessee state line, one in the Little River in Tennessee, and one in the Paint Rock River in Alabama.  The Clinch River population extends into two tributaries in Virgina, Copper Creek and Little River.  Initial steps have been taken for it to be reintroduced to the Tennessee River in Alabama and the lower Holston and French Broad rivers, both in Tennessee. 

All surviving populations continue to be threatened by many of the same factors identified at the time of listing e.g., habitat fragmentation, loss, and alteration resulting from impoundments; operation of hydroelectric dams; mining; wastewater discharges; water withdrawal; competition and displacement by non-native species; and the runoff of silt and other pollutants from ground disturbance activities. 

Scientific Name

Fusconaia cuneolus
Common Name
fine-rayed pigtoe
Finerayed pigtoe
FWS Category
Clams
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Habitat

Characteristics
Habitat

The finerayed pigtoe is associated with clean, fast-moving water with relatively stable cobble, gravel, and sand substrates free of siltation.  The mussel is usually found buried in the substrate in shallow riffle, ford, and shoal areas but can also occur in deeper runs.   

River or Stream

A natural body of running water.

Characteristic category

Food

Characteristics
Food

The finerayed pigtoe is a filter feeder, feeding by straining small organisms and food particles from the water. 

Characteristic category

Physical Characteristics

Characteristics
Size & Shape

A medium-sized mussel that can grow up to 2.5 inches in size.  It has an ovoid shell; the hinged end of the shell is rounded with a straight front margin.  The valves are subtriangular or subromboidal, and moderately full beaks curved forward.  

Color & Pattern

The outer shell is a greenish yellow to light brown and is indistinctly patterned with fine rays and growth lines.  The inner shell surface is white.

Characteristic category

Life Cycle

Characteristics
Reproduction

The lifecycle of the finerayed pigtoe is similar to other river mussels.  Males produce sperm which are discharged into the water and dispersed by currents.  Any downstream female of the same species obtains these sperm during filter feeding.  Fertilization of the female’s eggs by the sperm occurs within the gills of the female.  The fertilized eggs are retained in brood pouches, which are a modified section of the gills, to develop into larvae called glochidia.  Once developed the females release the glochidia into the water.  The glochidia must attach themselves to an appropriate fish host. After riding around on the fish for several weeks the glochidia will fall off the fish and settle on the bottom of the river or stream.  

The finerayed pigtoe is a short-term brooder.  Short-term brooders breed in the spring and early summer and release glochidia by mid to late summer.   

Geography

Characteristics
Range

The finerayed pigtoe is presently known from several tributaries of the Tennessee River above Muscle Shoals, AL; these include the North Fork Holston, Clinch (including Copper Creek and Little River in Virginia), Powell, Little, and Paint Rock rivers.   

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Timeline

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