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Rock Pocketbook (Arcidens confragosus)



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 where there is current. Five fish species have been recorded as its host including eel, drum, shad, rockbass and crappie.

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

The table below provides information about the protected status - both state and federal - and the rank (S and G Ranks) for Rock Pocketbook (Arcidens confragosus). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where occurrences of this species meet NHI data standards and is not meant as a comprehensive map of all observations.

Note: Species recently added to the NHI Working List may temporarily have blank occurrence maps.

Documented locations of Arcidens confragosus in the Natural Heritage Inventory Database as of July 2015.
Summary Information
State StatusTHR
Federal Status in Wisconsinnone
State RankS1S2
Global RankG4
Tracked by NHIY

Species guidance

Note: a species guidance document is not available at this time. Information below was compiled from publication PUB-ER-085-99 (now out-of-print).

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 Guidelines: 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.



Rock Pocketbook

Photo ©  Illinois Natural History Survey.

Last revised: Tuesday, February 19, 2019