Speckled Pocketbook

The speckled pocketbook is a bivalve mollusk belonging to the family Unionidae, commonly referred to as freshwater mussels, naiads, or clams. Each freshwater mussel is composed to two halves (valves) of a hard outer shell with the living animal (soft tissues) residing securely inside. The speckled pocketbook, scientific name Lampsilis streckeri, was described as a species new to science in 1927 by Lorraine Screven Frierson, a naturalist and landowner/merchant/planter residing south of Shreveport in the company town of Frierson, Louisiana. Frierson named the species in honor of his friend, colleague, and fellow naturalist John K. Strecker of Waco, Texas.

Adults may reach a length of slightly more than 3.5 inches (or more than 90 millimeters), with a maximum life expectancy of ten to twelve years. Speckled pocketbooks are sexually dimorphic—that is, males and females have slightly different shell shapes. The shell is elliptical to oblong ovate in outline, only slightly inflated, while the posterior end is somewhat pointed in males and more broadly rounded and slightly more inflated in females. The outer surface of the shell (periostracum) is smooth with tan to yellowish brown base coloration and numerous color rays that are thin to broad, dark green to black, wavy or broken. Some have chevron-shaped spots, often covering more of the shell than the base coloration. The inside of the shell (nacre) is salmon-colored to white and often iridescent on theposterior portion.

The speckled pocketbook is endemic to the Little Red River drainage (White River system) in the Ozark Mountains of north-central Arkansas. Once thought to persist only in the Middle Fork Little Red River, it currently is found in the Archey Fork, Middle Fork, South Fork, Turkey Fork, and Beech Fork of the Little Red River and Big Creek. It occurs in a variety of microhabitats within these streams, including: 1) low-velocity shallow glides with gravel and sand substrate, 2) deeper glides in sand/gravel-filled crevices between boulders or bedrock fissures, 3) deeper glides in sand/gravel underneath slab rock boulders, 4) low-gradient riffles dominated by cobble substrate with lower percentages of boulder and large gravel, and 5) pools with sand/gravel accumulated between large rocks and boulders (generally along the downslope of the bank).

Speckled pocketbooks are not found in lakes or ponds and are not able to adapt their life strategies (feeding, reproduction, etc.) to impounded waters. The speckled pocketbook was listed as a federally protected endangered species by the U.S. Fish and Wildlife Service in February 1989, and the recovery plan identified reservoir construction (specifically Greers Ferry Lake), water pollution, and channel modifications as contributors to the decline of the species. More-recent assessments identified threats associated with: 1) land use practices, including unrestricted cattle access to streams, eroding stream banks, and gravel mining, and 2) natural-gas exploration and development in the Fayetteville Shale formation, including dewatering or decreased base flows, habitat fragmentation, increased sedimentation, pollution runoff, and chemical spills. Despite these threats, the speckled pocketbook continues to exist in relatively healthy populations within its small geographic range.

Freshwater mussels reproduce by males releasing into the water column sperm that are taken up by females during filter feeding and respiration. Females release eggs from the gonads to a chamber within their body where fertilization occurs, and then the thousands of fertilized eggs are moved to the gills (ctenidia) for brooding in the marsupium until they develop into a parasitic larval form. Nearly all freshwater mussels have parasitic larvae that complete development to the juvenile stage while attached to fish. The larval form found in freshwater mussels like the speckled pocketbook is called a glochidium. Glochidia are small bivalves that attach to the fish host by clamping the shell valves on fins or gill filaments, with subsequent encapsulation in a cyst.

Most members of the genus Lampsilis have highly developed structures called mantle flaps that are among the best-known features of mussel biology. The mantle flaps mimic a food item of the host fish, such as a minnow in the case of the speckled pocketbook, and the movement of the mantle flap entices the fish to strike. In Lampsilis, the marsupia typically protrude between the shell valves and the mantle flaps during lure display. The attack by the host fish ruptures the marsupia and releases glochidia, which attach and encyst on the host fish gills. There, they reside for a period of up to forty-eight days before excysting and dropping to the stream bottom as a young speckled pocketbook.

Speckled pocketbook females have been observed carrying young within the marsupia (termed gravid) from February through August. Speckled pocketbook glochidia successfully transformed to juveniles in lab trials on seven fish species that included shadow bass (Ambloplites ariommus), green sunfish (Lepomis cyanellus), longear sunfish (L. megalotis), warmouth (L. gulosus), bluegill (L. macrochirus), smallmouth bass (Micropterus dolomieu), and spotted bass (M. punctulatus),

The U.S. Fish and Wildlife Service noted in a five-year status review in 2007 that the outlook for the speckled pocketbook has improved due to better understanding of its geographic distribution and population characteristics. Despite this optimism, the small extent of occupied habitat and myriad potential threats dictate that the speckled pocketbook remain federally protected as an endangered species for the foreseeable future.

For additional information:
Barnhart, M. C., W. R. Haag, and W. N. Roston. “Adaptations to Host Infection and Larval Parasitism in Unionoida.” Journal of the North American Benthological Society, 27, no. 2 (2008): 370–394.

Frierson, L. S. A Classified and Annotated Check List of the North American Naiades. Waco, TX: Baylor University Press, 1927.

Haag, W. R. North American Freshwater Mussels: Natural History, Ecology, and Conservation. Cambridge, UK: Cambridge University Press, 2012.

Harris, J. L., and M. E. Gordon. Arkansas Mussels. Little Rock: Arkansas Game and Fish Commission, 1990.

Harris, J. L., W. R. Posey II, C. L. Davidson, J. L. Farris, S. Rogers Oetker, J. N. Stoeckel, B. G. Crump, M. Scott Barnett, H. C. Martin, M. W. Matthews, J. H. Seagraves, N. J. Wentz, R. Winterringer, C. Osborne, and A. D. Christian. “Unionoida (Mollusca: Margaritiferidae, Unionidae) in Arkansas, Third Status Review.” Journal of the Arkansas Academy of Science 63 (2009): 50–86. Online at http://libinfo.uark.edu/aas/issues/2009v63/v63a8.pdf (accessed September 8, 2021).

Robison, Henry W., and Robert T. Allen. Only in Arkansas: A Study of the Endemic Plants and Animals of the State. Fayetteville: University of Arkansas Press, 1995.

U.S. Fish and Wildlife Service. “Endangered and Threatened Wildlife and Plants; Endangered Status for the Speckled Pocketbook (Lampsilis streckeri).” Federal Register 54.38 (1989):8339–8341.

U.S. Fish and Wildlife Service. “Speckled Pocketbook (Lampsilis streckeri Frierson 1927) 5-Year Review: Summary and Evaluation.” Conway, AR: USFWS Ecological Services Field Office, 2007.

U.S. Fish and Wildlife Service. “Speckled Pocketbook Mussel (Lampsilis streckeri) Recovery Plan.” Jackson, MS: U.S. Fish and Wildlife Service, 1991.

Winterringer, R. “Population Dynamics and Reproductive Patterns of the Federally Endangered Freshwater Mussel, Lampsilis streckeri (Frierson 1927).” MS thesis, Arkansas State University, 2003.

John Harris
Scott, Arkansas