Tritogonia verrucosa

Geographic Range

Tritogonia verrucosa , the buckhorn (also called pistol grip), is found in the Neartic region. Buckhorns have been documented in the mid and eastern parts of the United States, including: Texas, Pennsylvania, Tennessee, Mississippi, Kentucky, Georgia, Alabama, Minnesota, Missouri, Iowa, Arkansas, Louisiana, Maryland, Oklahoma, Delaware, North Carolina, Ohio, Indiana, Wisconsin, Illinois, West Virginia, and Virginia.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Buckhorn are usually found in medium or large sized rivers where they burrow in sand and gravel substrates. Buckhorn have also been recorded in mud or silt substrates.

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• benthic benthic
• rivers and streams

Physical Description

Buckhorn have a thick shell that is normally elongate. The entire shell (except the rounded posterior ridge of the female) has pustules of atypical sizes and shapes. Male shells are truncated, and females are compressed with a dorsal margin that is straight to slightly curved, with the ventral margin usually arched. The sculpture of the beak (umbo) is a series of pronounced ridges continuing down the sides. Shell color is green or light brown with green coloration, but with age, becoming dark brown to black in older shells.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes shaped differently

Development

Buckhorn males release sperm into the water, which is then taken in by females through their incurrent siphon. The buckhorn is tachytictic, which means it spawns in spring and its bivalved larvae (glochidia) are released in summer. Females brood the fertilized eggs in their gills from May to August. After the eggs develop into glochidia they are released. Glochidia then attach to fish gills by clamping with their valves in a vise like fashion. While attached to the fish, they transform to juveniles. The juveniles then release from the gills of the fish and fall to the substrate of the aquatic system where they are found.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Male buckhorns release sperm into the water in spring, and the sperm are taken in indiscriminately by the females' incurrent siphons. The buckhorn is tachytictic, which means it spawns in spring and its bivalved larvae (glochidia) are released in summer.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Once eggs are fertilized, the female broods them until they develop to glochidia. The glochidia released from the female are obligate parasites on fish. They will attach to the fish and metamorphose to juveniles, and then become independent living mussels.

Glochidia length for buckhorns is on average 0.122 mm with a deviation of 0.003 mm. Width is a mean of 0.109 mm with a deviation of 0.003 mm. Hinge length is a mean of 0.049 mm with a deviation of 0.003 mm. The number of glochidia detected in one study was 1.8 offspring per 100 cubic meters.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• simultaneous hermaphrodite
• sexual sexual
• fertilization fertilization
  • internal internal
• broadcast (group) spawning
• ovoviviparous ovoviviparous

The extent of parental investment for buckhorn females is to brood glochidia in their gills supplying nutrients until they are released into the environment. The only investment of buckhorn males is their gamete donation.

• Parental Investment
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

The most effective method to age bivalves is to use internal growth rings as indicators, however, no ageing studies have been done for Tritogonia verrucosa . Unionid mussels in general are long lived, sometimes living up to seven decades.

Behavior

Buckhorn mussels are sedentary for most of their lives, but can move within the sediments by use of its foot.

• Key Behaviors
• parasite parasite
• motile motile
• sedentary sedentary

Home Range

The home range for buckhorns is unknown. Adult mussels move only a few meters from where they settle as juveniles.

Communication and Perception

Unionid mussels in general maintain equilibrium with statocysts and the statoliths, which help them sense gravity. Mussels respond to touch through tactile cells on the mantle. Mussels may detect vibrations, and some females will release glochidia when a shadow passing over them, as a potential host fish would. Spawning and potentially other behaviors such as glochidial release, may be a response to chemical cues. Buckhorn glochidia will snap shut in response to touch, which is a response needed to successfully attach to a fish host.

• Communication Channels
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

Buckhorn mussels extract nutrients and oxygen from detritus and water through their incurrent siphon, and discharge waste products through their excurrent siphon.

• Primary Diet
• detritivore detritivore

• Plant Foods
• algae
• phytoplankton phytoplankton

• Other Foods
• detritus detritus
• microbes

• Foraging Behavior
• filter-feeding filter-feeding

Predation

Buckhorn mussels have a hard shell which protects them from predators. Their shell and mantle coloration helps them blend into thier habitat. In general, unionid mussels are preyed upon by ducks and geese ( Anatidae ), raccoons ( Procyon lotor ), river otters ( Lontra canadensis ), and muskrats ( Ondotra zibethicus ). No documentation of any specific species has been observed to actively prey on buckhorn mussels.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Within mussel beds there has been a positive correlation with species richness, and an increase in all macro-faunal groups. Host fish for buckhorn mussels include flathead catfish ( Pylodictis olivaris ), brown bullhead ( Ameiurus nebulosus ) and yellow bullhead ( Ameiurus natalis ). The introduction of zebra mussels ( Dreissena polymorpha ) has had a detrimental effect on native mussels as they attach themselves in large numbers to the shells, eventually causing death by starvation. Conchophthirus curtis , a kind of ciliate parasite, is found in buckhorn mussels.

• Ecosystem Impact
• biodegradation biodegradation
• parasite parasite

Economic Importance for Humans: Positive

At one time buckhorns were used in large numbers for making pearl buttons for clothing. The shells have also been used to seed marine oysters to stimulate growth of valuable pearls. Mussels in general are indicators of water quality since they are long-lived and sedentary.

• Positive Impacts
• body parts are source of valuable material
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Tritogonia verrucosa on humans.

Conservation Status

Tritogonia verrucosa is listed as threatened by the states of Minnesota, Virginia, and Wisconsin through their individual state conservation programs. In North Carolina, this species is listed as extirpated.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Jacob Pederson (author), Minnesota State University, Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Renee Mulcrone (editor), Special Projects, Catherine Kent (editor), Special Projects.

References

Amyot, J., J. Downing. 1997. Seasonal variation in vertical and horizontal movement of the freshwater bivalve Elliptio complanata . Freshwater Biology , 37: 345-354. Accessed February 27, 2012 at http://www.public.iastate.edu/~downing/tier%202/jadpdfs/1997%20FB%20Seasonal%20Variation%2037.%20345-354.pdf .

Antipa, G., E. Small. 1971. The occurrence of Thigmotrichous ciliated protozoa inhabiting the mantle cavity of unionid molluscs of Illinois. American Microscopical Society , 90 (4): 463-472. Accessed February 27, 2012 at http://www.jstor.org/stable/3225461?seq=3 .

Borthagaray, A., A. Carranza. 2006. Mussels as ecosystem engineers: Their contribution to species richness in a rocky littoral community. Acta Oecologica , 31 (3): 243-250.

Comfort, A. 1957. The duration of life in molluscs. Journal of Molluscan Studies , 32 (6): 219-241.

Cummins, K., C. Mayer. 1997. " Tritogonia verrucosa (Rafinesque, 1820)" (On-line). Field guide to freshwater mussels of the midwest, Illinois Natural History Survey Manual 5. Accessed February 27, 2012 at http://www.inhs.illinois.edu/animals_plants/mollusk/musselmanual/page26_7.html .

Jirka, K., R. Neves. 1992. Reproductive biology of four species of freshwater mussels (Mollusca:Unionidae) in the New River, Virginia and West Virginia. Journal of Freshwater Ecology , 7 (1): 35-45. Accessed February 27, 2012 at http://www.fishwild.vt.edu/mussel/PDFfiles/reproduction_biology.pdf .

Kidwell, S., T. Rothfus. 2010. The living, the dead, and the expected dead: variation in life span. Paleobiology , 36(4): 615–640. Accessed February 27, 2012 at http://geosci.uchicago.edu/pdfs/kidwell/KidwellRothfus2010Paleobio.pdf .

Minnesota Dept. of Natural Resources, 2012. " Tritogonia verrucosa (Rafinesque, 1820)" (On-line). Minnesota Department of Natural Resources Rare Species Guide. Accessed February 27, 2012 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=IMBIV44010 .

Missouri Dept. of Conservation, 2011. "Pistolgrip (also Buckhorn)" (On-line). Field Guide, Aquatic Invertebrates. Accessed February 27, 2012 at http://mdc.mo.gov/discover-nature/field-guide/pistolgrip-also-buckhorn .

Smith, A., S. Jepsen. 2008. Overlooked gems: The benefits of freshwater mussels. WINGS , Fall: 14-19. Accessed February 27, 2012 at http://www.xerces.org/wp-content/uploads/2009/01/mussel_article.pdf .

Wang, S., A. Bush. 2008. Adjusting global extinction rates to account for taxonomic susceptibility. Paleobiology , 34(4): 435-455. Accessed February 27, 2012 at http://www.swarthmore.edu/NatSci/swang1/Publications/pbio2008b.pdf .

Winhold, L. 2004. "Unionidae" (On-line). Animal Diversity Web. Accessed February 27, 2012 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Unionidae.html .

Wisconsin Dept. of Nat. Resources, 2009. "Endangered Resources Program Species Information" (On-line). Buckhorn ( Tritogonia verrucosa ). Accessed February 27, 2012 at http://dnr.wi.gov/org/land/er/biodiversity/index.asp?mode=info&Grp=19&SpecCode=IMBIV44010 .