Endangered Resources Program Species Information
Rock Pocketbook (Arcidens confragosus)

Overview

Species Overview

Rock pocketbook (Arcidens confragosus), a mussel listed as Threatened in Wisconsin, is found in large rivers in the western part of the state. It is found in all substrate types were there is current. Five fish species have been recorded as its host including eel, drum, shad, rockbass and crappie.

Status and NHI Documented Occurrences in Wisconsin

The table below provides information about the protected status (State and Federal Status) and the rank (S and G Ranks) for Rock Pocketbook (Arcidens confragosus). See the Working List Key for more information about the abbreviations used. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. For invertebrates, dots depict locations from the "Invertebrate Atlas," a database with occurrences of rare and common aquatic and select terrestrial invertebrate species found in Wisconsin and adjacent areas. While the invertebrate atlas is a quality assured database, not all records have been verified. The map is provided as a general reference of where this species has been found to date and is not meant as a range map.

Summary Information State Status: THR Federal Status in Wisconsin: none State Rank: S1S2 Global Rank: G4 Tracked by NHI: Y Species of Greatest Conservation Need: Y

Detailed Information

Identification: Shell is thin to moderately thick and inflated. Umbos are elevated and located near the middle of the shell. Sculpturing consists of two rows of knobs that continue onto the posterior part of the shell and form into folds. The outside of the shell is olive-green to green. Larger shells become black, thicken and may lose the crinkly appearance, while the younger, smaller shells are greenish. Pseudocardinal teeth are narrow and elongated, while lateral teeth are indistinct. Nacre is white and iridescent posteriorly. Length to 7 inches (17.8 cm).

Habitat: Most often found in sluggish water at shallow depths of less than one meter on a firm mud bottom. Inhabitants of quiet pools on a mud or stable sand bottom.

State Distribution: Occurs in the Mississippi River and the lower Wisconsin River.

Phenology: The species is a winter breeder. Glochidia are present in the latter part of January and embryos in the middle of March. Host fish are known to be freshwater drum (Aplodinotus grunniens), American eel (Anguilla rostrata), gizzard shad (Dorosoma cepedianum), rock bass (Ambloplites rupestris), and white crappie (Pomoxis annularis). Breeding occurs from September to June.

Management Guidance: Habitat destruction and river pollution have resulted in mussel declines. Protection of habitat and improvements in water quality along with restriction of dredging, impoundments, sand and gravel mining, and navigational improvements would benefit this species.

Information compiled from publication PUB-ER-085-99 (now out-of-print).

Photos

Click on a photo to view a larger version. Please considering donating your photos to the Endangered Resources Program for educational uses. See also information regarding use of photos

Photo ©  Illinois Natural History Survey.

Related Links

Links to Additional Rock Pocketbook Information

• Illinois Natural History Survey [Exit DNR]
• MN Department of Natural Resources [Exit DNR]

Other Links Related to Mussels and Clams

• Illinois Natural History Survey [Exit DNR]
• The Field Museum [Exit DNR]
• Conchologists of America [Exit DNR]
• EPA Biological Indicators of Watershed Health [Exit DNR]
• Milwaukee Public Museum [Exit DNR]