Lampsilis bracteata

Texas Fatmucket

FWS Focus

Overview

Characteristics
Overview

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

Scientific Name

Lampsilis bracteata
Common Name
Texas fatmucket
FWS Category
Clams
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Food

Characteristics
Food

Like all other freshwater mussel species, Texas fatmucket are filter feeders that feed and survive on organic particulate matter, bacteria 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.

Characteristic category

Behavior

Characteristics
Behavior
Characteristic category

Similar Species

Characteristics
Similar Species
Characteristic category

Life Cycle

Characteristics
Life Cycle

The Texas fatmucket, 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 female then attracts host fish through the use of a mantle lure mimicking fish prey of its hosts. 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, meaning break away, from the host and settle on the stream bottom leaving their host relatively unharmed.

Reproduction

Texas fatmucket are considered to be long-term brooders, or bradytictic, and are believed to have a peak reproductive season between February and July. Four fish hosts have been reported, including: bluegill (Lepomis macrochirus), green sunfish (L. cyanellus), Guadalupe bass (Micropterus treculii) and largemouth bass (M. salmoides).

Life Span

Texas fatmucket collected from the San Saba and Llano rivers have been determined to reach ages of at least 15 years. Similar to the Texas fatmucket, congeners (Lampsilis spp.) from the southeast United States were reported by Haag and Rypel in 2010 to reach a maximum age of 13 to 25 years.

Characteristic category

Physical Characteristics

Characteristics
Size & Shape

The Texas fatmucket is a small to medium-sized freshwater mussel with an elliptical to sub-rhomboidal shell. The beaks are elevated above the hinge line with fine V-shaped ridges. The shell disc lacks sculpturing and has a broadly rounded posterior ridge. Pseudocardinal teeth, which are molar-like structures located near the beaks on the interior surface, are thin and compressed and lateral teeth, with two in the left valve and one on the right, are slightly curved and lamellar.

Measurements
Length: up to 4 in (100 mm)

Color & Pattern

The exterior shell with often broken black or brown rays that broaden near the margin. The interior shell surface, or nacre, is typically white, with an occasional salmon or yellow tint.

Characteristic category

Habitat

Characteristics
Habitat

The Texas fatmucket is known to inhabit flowing streams and rivers of the Edwards Plateau, with substrates of stable sand, firm mud, stable sand and gravel bottoms. In shallower waters, they can sometimes be found in bedrock fissures or among roots of bald cypress and other aquatic vegetation.

River or Stream

Geography

Characteristics
Range

Texas fatmucket appears to be currently restricted to upper reaches of major tributaries within the Colorado River Basin. The total current distribution of Texas fatmucket, summed across the five populations from the Colorado River Basin, is a combined stream length of approximately 295 miles across 11 counties.

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