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Species Description

Mountain Creekshell

Villosa vanuxemensis


Classification

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

Description

The Mountain Creekshell is a small freshwater mussel that is usually less than 2.75 inches (70 mm) in length. Its shell is nearly oval in shape. The periostracum is (outer shell surface) tan, olive or dark brown and becomes black in older specimens. The surface may be marked with narrow rays, but they are often not distinct and may be absent altogether. The nacre (inner shell surface) color is variable, ranging from shades of purple to copper.

Life Cycle

Freshwater mussels have complex life cycles. Male Mountain Creekshell mussels release sperm into creeks and streams. 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. This species is believed to be bradytictic (a long-term brooder). Bradytictic species spawn during the summer and females release mature glochidia the following spring. Parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. Several species of Sculpin have been identified as suitable host fish, including the Banded Sculpin (Cottus carolinae), Black Sculpin (C. baileyi), Slimy Sculpin (C. cognatus) and the Mottled Sculpin (C. bairdi). The glochidia parasitize a fish host for a variable length of time, likely depending upon water temperature, fish species and other factors. Larvae transform into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the sand or gravel bottom of a creek or stream.

Natural History

Mountain Creekshell l arvae (glochidia) are parasitic upon tissue of fish hosts while completing the metamorphosis into juvenile mussels. Adult mussels are typically sessile and are found attached or buried in the sand or gravel bottoms of creeks and streams. The Mountain Creekshell is also often found near Water Willow (Justicia americana ) beds in clean, shallow water that is less than 3 feet deep. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. M ussels 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 its gills and food particles are trapped and eventually digested.

Range

The Mountain Creekshell is found in the Tennessee River Basin , Central Cumberland River Basin and Coosa River system. Its range covers portions of Georgia , Tennessee , North Carolina , Virginia and Kentucky . Within northwestern Georgia , the Mountain Creekshell is found in the Conasauaga River .

Conservation Status

The Mountain Creekshell is listed as Uncommon or Rare in Georgia . Like many freshwater mussels, this species has likely been adversely affected by pollution, habitat degradation and excess sedimentation.

Similar Species

The Mountain Creekshell can be difficult to distinguish from other small, brown or black mussels within its range. Identification of this species should probably be verified by a malacologist (an individual that studies mollusks).