Quadrula petrina

Texas Pimpleback

FWS Focus

Overview

Characteristics
Overview

This Texas-endemic freshwater mussel species is only known to occur in the Texas Hill Country's Colorado River and its tributaries. Like many other freshwater mussels, the proposed endangered Texas pimpleback has a unique life cycle that requires the use of a host fish, including catfish species, to transform the immature larva stage into a self-supporting juvenile mussel. The species is small to medium in size and has a yellow to tan shell with vague green rays or concentric blotches. The Texas pimpleback's distribution has been relegated to five known populations across 11 counties in central Texas.

Scientific Name

Quadrula petrina
Common Name
Texas pimpleback
FWS Category
Clams
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Habitat

Characteristics
Habitat

The Texas pimpleback occurs in medium to large-sized streams and rivers in riffle and run habitats of heterogenous substrates, or sometimes in gravel-filled cracks in the bedrock, often at depths less than 2 meters and aren’t known to tolerate impoundments.

River or Stream
Characteristic category

Behavior

Characteristics
Behavior
Characteristic category

Physical Characteristics

Characteristics
Size & Shape

The Texas pimpleback is a small to medium-sized freshwater mussel with a moderately inflated, subquadrate to suboval shell. The shell’s beaks are full, high and elevated above the hinge line with two to four rows of sculpturing on the umbo. The shell disc typically lacks sculpturing but has parallel ridges along its broadly rounded posterior slope. The interior shell surface, or nacre, is typically white and iridescent. 

Measurements
Length: Approaching 4 in (100 mm)

Color & Pattern

Texas pimpleback's shell colors range from yellow to tan, brown to black and will occasionally have vague green rays or concentric blotches, but these markings are not considered to be diagnostic shell characters. 

Characteristic category

Life Cycle

Characteristics
Life Cycle

The Texas pimpleback, like all freshwater mussels, has an interesting life history. Males release sperm into the water column, which is taken in by the female fertilizing her eggs. The developing larvae are held by the female until they mature and are ready for release. The mature larvae, called glochidia, are released in proximity to a fish host and attach to the host’s gills or fins. Glochidia that fail to attach to a suitable host or attach to the wrong location will die. Attached glochidia encyst or implant into the host and develop into juvenile mussels over a period of weeks or months. Once fully developed, the juveniles excyst, or break away, from the host and settle on the stream bottom leaving their host relatively unharmed.

Reproduction

Texas pimpleback are considered to be short-term brooders, or tachytictic. It is expected that the species utilizes similar host fishes as those identified for the closely related Guadalupe orb, including channel catfish (Ictalurus punctatus), flathead catfish (Pylodictis olivaris), yellow bullhead (Amerius natalis) and tadpole madtom (Noturus gyrinus). 

Life Span

While no age at maturity information exists for Texas pimpleback, similar species like congeners (Quadrula spp.; now Cyclonaias) and members of tribe Quadrulini have reached a maximum age of 15 to 72 years and 15 to 91 years, respectively.

Characteristic category

Food

Characteristics
Food

Like all other freshwater mussel species, Texas pimpleback are filter feeders that feed and survive on organic particulate matter, bacteri, and algae that are filtered from the water column. Juvenile mussels live in the sediment and most likely feed interstitially rather than from the water column, using the relatively large muscular foot to sweep organic and inorganic particles found among the substrate into the shell opening.

Geography

Characteristics
Range

The Texas pimpleback is endemic to the Colorado River Basin in Texas and has been documented in five populations across 11 Texas counties.

Launch Interactive Map

Timeline

Explore the information available for this taxon's timeline. You can select an event on the timeline to view more information, or cycle through the content available in the carousel below.

15 Items