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Species Description

Fine-lined Pocketbook

Lampsilis altilis


Classification

Phylum: Mollusca
Subphylum:
Class: Bivalvia
Order: Unionoida
Family: Unionidae

Description

Lampsilis altilis is a medium-sized freshwater mussel that rarely measures more than 4 inches (100 mm) in length. It has a nearly oval-shaped shell that is yellow brown to blackish in color and marked with fine rays. The nacre (inner shell surface) is white and appears iridescent in the posterior region. Female Fine-lined Pocketbooks can be distinguished by a distinctive pointed posterior margin.

Life Cycle

Many of the specific details about the life cycle of this threatened mussel are not currently known, but the life history of Lampsilis altilis is presumed to be similar to related species. Male Fine-lined Pocketbooks release sperm into the water column of swift-flowing creeks and smaller rivers. Sperm enters females through siphon-like regions and fertilization of eggs occurs within female shells. These fertilized eggs develop into special larva called glochidia. Glochidia continue to develop and are released into the water column when fully matured. Glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. Recent research suggests that Lampsilis altilis may parasitize several species within the Sunfish family (Centrarchidae) for varying lengths of time, likely depending upon water temperature, fish species and other factors. The larvae metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the gravel or sandy bottoms of creeks and smaller rivers within its limited range.

Natural History

Many of the details about the natural history of the Fine-lined Pocketbook are not currently known, but they are presumed to be similar to better known, related species. Larvae (glochidia) are parasitic upon tissue of fish hosts while completing the metamorphosis into juvenile mussels. Adult mussels are typically sessile and are often found attached to the sandy or gravel bottom of swiftly flowing creeks and rivers. They are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Fine-lined Pocketbook mussels bring water from their habitat into their shells through specialized regions that are similar to the true siphons of clams. The water is then filtered over the gills and food particles are trapped and eventually digested. Water is then pushed back out another siphon-like region.

Range

Historically, the Fine-lined Pocketbook was widespread throughout the Mobile River Basin region of Georgia , Tennessee and Alabama . However, today it is scattered throughout a limited number of fast flowing creeks and small rivers within its historic range. Within Georgia it is only found in the Conasauga and Coosa Rivers of Chattooga, Murray, Walker and Whitfield counties.

Conservation Status

The Fine-lined Pocketbook is currently listed as threatened within its limited range by state and federal agencies. Freshwater mussels are very susceptible to degradation and changes within their habitat, especially from pollution and the construction of impoundments. Another factor that has likely contributed to the dwindling numbers of Fine-lined Pocketbooks and other mussels is increased sedimentation. Sedimentation can cause suffocation and can severely interfere with the effective filter feeding of mussels.

Similar Species

The most similar species to the Fine-lined Pocketbook mussel is the Orange-nacre Mucket (Lampsilis perovalis). Lampsilis altilis can be distinguished by the white nacre (internal shell surface), fine ray markings on the outer shell and more elongate shape of its shell.