The Guadalupe Orb is a rare mussel that was first identified as a unique species, exclusively found in the Guadalupe River Basin, in 2018. The mussel was originally thought to be a variation of the Texas pimpleback, which is found in the Colorado River Basin (Burlakova 2018). In September of 2021, the United States Fish and Wildlife Service (USFWS) proposed the Guadalupe Orb for listing as endangered under the ESA and designated critical habitat in the Guadalupe and San Marcos rivers. This decision was based on a completed species status assessment for six central Texas mussels that identified declining populations as a result of reduced water quality and habitat destruction.
Federal Endangered Species Act Status:
Candidate – Under Review
State of Texas Species Conservation Status:
Kerr, Kendall, Comal, Guadalupe, Caldwell, Gonzales, DeWitt, and Victoria counties
The Guadalupe Orb is a medium sized freshwater mussel with rounded edges, and an offset hinge. The mussel is commonly yellow to brown or black in color and often has green lines that run from the hinge line to the edge of the shell. This mussel frequently has unique sculptured distortions (Howells 2014).
The Guadalupe Orb can live for at least 15 years (Howells 2010d). The mussels begin holding mature glochidia (larval stage of mussels) shortly after spawning between March and June (Dudding 2020). The mussels are short-term brooders, and release glochidia shortly after they mature, which subsequently attach to the gills of a variety of catfish fish hosts (Dudding 2018). The attached glochidia will transform into juvenile mussels after about a month and fall onto the substrate of the waterbody where they will burrow for protection and continue development into adult mussels.
Habitat and Diet:
Guadalupe Orb adults are filter feeders that siphon plankton, organic matter and small organisms out of the water and sediment. The juvenile glochidia receive nourishment from the gills of a fish host. The adults are found in riffles and runs of moderately sized rivers in water depths of 0.5 to 1.0 meter and substrates of mud, silt, gravel and cobble. They require dissolved oxygen concentrations of at least 2 mg/L, water temperatures of less than 26°C (79°F), and total ammonia nitrogen concentrations of less than 0.5 mg/L (USFWS SSA 2018).
Burlakova, L., Karatayev, A., Froufe, E., Bogan, A.E., and Lopes-Lima, M. (2018). A new freshwater bivalve species of the genus Cyclonaias from Texas (Unionidae: Ambleminae: Quadrulini) The Nautilus 132(2), 45-50.
Dudding, J., Hart, M., Morton, J., Robertson, C., Conway, K., Lopez, R., and Randklev, C. (2018). Host fish association for two highly imperiled mussel species from the southwestern United States: Fusconaia mitchelli (false spike) and Cyclonaias petrina (Texas Pimpleback). Thesis submitted to Texas A&M University. College Station, Texas.
Dudding, J. Hart, M., Khan, J.M., Robertson, C.R., Lopez, R., and Randklev, C.R. (2020). Reproductive life history of 2 imperiled and 1 widely distributed freshwater mussel species from the southwestern United States. Freshwater Science, 39(1).
Howells, R.G., Neck, R.W.. and Murray, H.D. (1996). Freshwater Mussels of Texas. Texas Parks and Wildlife Department Inland Fisheries Division. Austin, Texas.
Howells, R.G. (2010d). False spike (Quadrula mitchelli): Summary of Selected Biological and Ecological Data for Texas. BioStudies, 16
Howells, R.G. (2014). Field Guide to Texas Freshwater Mussels, 2nd edition. BioStudies, Kerrville, Texas. 141
Randklev, C. R., Johnson, N.A., Miller, T., Morton, J.M., Dudding, J., Skow, J., Boseman, B., Hart, M., Tsakiris. E.T., Inoue, K. and Lopez. R. R. (2017c). Freshwater Mussels (Unionidae): Central and West Texas Final Report. Texas A&M Institute of Renewable Natural Resources, College Station, Texas.
United States Fish and Wildlife Service. (2018). Species Status Assessment Report for the Central Texas Mussels: False Spike (Fusconaia mitchelli), Texas Fatmucket (Lampsilis bracteata), Texas Fawnsfoot (Truncilla macrodon), Texas Pimpleback (Cyclonaias petrina), Guadalupe Fatmucket (Lampsilis sp. Cf. bractceata), and Guadalupe orb (Cyclonaias necki). Albuquerque, New Mexico.