Spinymussel, James River

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Spinymussel, James River

Pleurobema collina

phylum: Mollusca

class: Bivalvia

order: Unionoida

family: Unionidae

status: Critically endangered, IUCN Endangered, ESA

range: USA (Virginia and West Virginia)

Description and biology

The James River spinymussel, also known as the Virginia spinymussel, is one of only three known freshwater spinymussels. These mussels are so-named because juveniles, or young, have one to three spines on each valve or shell. These spines are usually lost by the time the spinymussel reaches adulthood. An average adult has a shell length between 2 and 3.5 inches (5 and 8.9 centimeters). Spinymussels feed on plankton (microscopic plants and small animals) and other plant matter they strain from the water through a tube called a siphon.

Like other mussels, the James River spinymussel breeds in a unique way every spring. Males release sperm, which is carried away by river currents. Downstream, females take in this sperm while feeding. The eggs stored in their gills are then fertilized. When the eggs hatch, the glochidia (pronounced

glow-KID-ee-a) or larval forms of the mussel stay in the gills and continue to develop.

After a while, the glochidia are released into the river. They then attach themselves to the gills of a host fish (those glochidia that are unable to attach themselves float to the bottom of the river and die). When they have developed a shell and grown large enough to care for themselves, the young spinymussels detach from the host fish and sink to theriverbed. They bury themselves in the gravel or sand, leaving only their shell margins (edges) and siphons exposed.

Habitat and current distribution

This species of mussel is found in four headwater streams (streams that form the source of a river) of the James River. In Craig and Botetourt Counties in Virginia, it inhabits Craig, Catawba, and Johns Creeks. In Monroe County in West Virginia, it inhabits Potts Creek.

The James River spinymussel prefers clean, slow-flowing freshwater streams. Too much silt (mineral particles) or sediment (sand and stones) in the water can clog a spinymussel's siphon, eventually killing it.

History and conservation measures

The James River spinymussel was discovered in 1836 in the Calfpasture River in Rockbridge County, Virginia. At the time, the spinymussel inhabited most of the area drained by the James River. Its current range is less than 10 percent of that original range.

A primary factor in the spinymussels' decline has been habitat destruction. Land adjacent to rivers and streams throughout its range has been developed into farms and urban areas. Runoff from those farms, which includes pesticides, herbicides, and silt, has poisoned much of the spinymussels' habitat. It continues to do so.

The James River spinymussel is further threatened by the Asiatic clam. This introduced species has taken over much of the spinymussel's former habitat. The Asiatic clam eats the majority of phytoplankton (microscopic aquatic plants) in the water, robbing the James River spinymussel and other native mussels of the nutrients they need.