Fusconaia flava

Geographic Range

The Wabash pigtoe is found in the Mississippi drainage from Oklahoma and Tennessee to Minnesota and Pennsylvania. In the St. Lawrence it is found from Wisconsin to central New York and southern Ontario. In Canada it is found in the the Red River of the North, the Nelson River and Lake Winnipeg.

In Michigan, F. flava is found in the lower peninsula, from Muskegon River tributaries through the southern portion of the state. In the upper peninsula, it has been recorded in the Menominee and Sturgeon Rivers and the mouth of the Whitefish River.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

The Wabash pigtoe is found from creeks to large rivers with moderate current in mud, sand or gravel. However, it is more common in streams than rivers. On the Huron River, it seemed to prefer a firm bottom of sand and fine gravel. In the Clinton it was found on a firm sand bottom.

• Habitat Regions
• freshwater freshwater

• Aquatic Biomes
• rivers and streams

Physical Description

The Wabash pigtoe is up to 7.6 cm (3 inches) long , and is triangular to quadrate in shape. The shapes of headwater to river forms vary. Headwater forms are more rounded and river forms have a more prominent posterior ridge. The shell is fairly thick and compressed. The anterior end is gently rounded, the posterior end bluntly pointed. The dorsal margin is short and straight. The ventral margin is rounded anteriorly and bluntly pointed posteriorly.

Umbos are broad and raised slightly above the hinge line. The beak sculpture has three to four weak concentric bars.

The periostracum (outer shell layer) is smooth, yellowish-brown to dark brown in older individuals. Faint green rays are visible in younger individuals.

On the inner shell, the left valve has two pseudocardinal teeth , which are heavy, rough, and serrated. The anterior tooth is narrow and elongate, the posterior one is heavy and triangular. The two lateral teeth are short and straight. The right valve has one large, serrated, pseudocardinal tooth, and one (sometimes two) are short, straight and stout.

The beak cavity is deep and wide. Although the nacre is white, occasionally it is has a pink or salmon tint and is iridescent posteriorly.

In Michigan, identification of F. flava can be easily confused with Pleurobema sintoxia , particularly in upper reaches of river systems. The sulcus of F. flava becomes more prominent in more downstream populations, making it more distinguishable from P. sintoxia . The Wabash pigtoe generally has a deeper beak cavity. When present in females, glochidial packets from the Wabash pigtoe also tend to be orangish while the round pigtoe has white glochidial packets.

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

• Sexual Dimorphism
• sexes alike

Development

Fertilized eggs are brooded in the marsupia (water tubes) up to three months, where they develop into larvae, called glochidia. The glochidia are then released into the water where they must attach to the gill filaments and/or general body surface of the host fish. After attachment, epithelial tissue from the host fish grows over and encapsulates a glochidium, usually within a few hours. The glochidia then metamorphoses into a juvenile mussel within a few days or weeks. After metamorphosis, the juvenile is sloughed off as a free-living organism. Juveniles are found in the substrate where they develop into adults.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Age to sexual maturity for this species is unknown. Unionids are gonochoristic (sexes are separate) and viviparous. The glochidia, which are the larval stage of the mussels, are released live from the female after they are fully developed.

In general, gametogenesis in unionids is initiated by increasing water temperatures. The general life cycle of a unionid , includes open fertilization. Males release sperm into the water, which is taken in by the females through their respiratory current. The eggs are internally fertilized in the suprabranchial chambers, then pass into water tubes of the gills, where they develop into glochidia.

Fusconaia flava is a short-term brooder. In the Huron River in Michigan, the Wabash pigtoe was gravid from mid-May to mid-August. It probably breeds in early May.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• viviparous viviparous

Females brood fertilized eggs in their marsupial pouch. The fertilized eggs develop into glochidia. There is no parental investment after the female releases the glochidia.

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

Lifespan/Longevity

The age of mussels can be determined by looking at annual rings on the shell. However, no demographic data on this species has been recorded.

Behavior

Mussels in general are rather sedentary, although they may move in response to changing water levels and conditions. Although not thoroughly documented, the mussels may vertically migrate to release glochidia and spawn.

Fusconaia flava releases small, white, worm-like glochidial packets which resemble invertebrates that fish would eat. These mimics are likely used to get the glochidia to the host fish.

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

Communication and Perception

The middle lobe of the mantle edge has most of a bivalve's sensory organs. Paired statocysts , which are fluid filled chambers with a solid granule or pellet (a statolity) are in the mussel's foot. The statocysts help the mussel with georeception, or orientation.

Mussels are heterothermic, and therefore are sensitive and responsive to temperature.

Unionids in general may have some form of chemical reception to recognize fish hosts. How the Wabash pigtoe attracts or recognizes its fish host is unknown.

Glochidia respond to touch, light and some chemical cues. In general, when touched or a fluid is introduced, they will respond by clamping shut.

• Communication Channels
• chemical chemical

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

Food Habits

In general, unionids are filter feeders. The mussels use cilia to pump water into the incurrent siphon where food is caught in a mucus lining in the demibranchs. Particles are sorted by the labial palps and then directed to the mouth. Mussels have been cultured on algae, but they may also ingest bacteria, protozoans and other organic particles.

The parasitic glochidial stage absorbs blood and nutrients from hosts after attachment. Mantle cells within the glochidia feed off of the host’s tissue through phagocytocis.

• Primary Diet
• planktivore planktivore
• detritivore detritivore

• Plant Foods
• algae
• phytoplankton phytoplankton

• Other Foods
• detritus detritus
• microbes

• Foraging Behavior
• filter-feeding filter-feeding

Predation

Unionids in general are preyed upon by muskrats , raccoons , minks , otters , and some birds. Juveniles are probably also fed upon by freshwater drum , sheepshead , lake sturgeon , spotted suckers , redhorses , and pumpkinseeds .

Unionid mortality and reproduction is affected by unionicolid mites and monogenic trematodes feeding on gill and mantle tissue. Parasitic chironomid larvae may destroy up to half the mussel gill.

Ecosystem Roles

Fish hosts are determined by looking at both lab transformations and natural infestations. Looking at both is necessary, as lab transformations from glochidia to juvenile may occur, but the mussel may not actually infect a particular species in a natural situation. Natural infestations may also be found, but glochidia will attach to almost any fish, including those that are not suitable hosts. Lab transformations involve isolating one particular fish species and introducing glochidia either into the fish tank or directly inoculating the fish gills with glochidia. Tanks are monitored and if juveniles are later found the fish species is considered a suitable host.

In lab trials, Fusconaia flava metamorphosed on the creek chub and the silver shiner . Although the common shiner has not been tested in lab trials, F. flava populations in Michigan were high in areas where the common shiner was found. This implies that the common shiner may be a host fish.

• Ecosystem Impact
• parasite parasite

Economic Importance for Humans: Positive

Mussels are ecological indicators. Their presence in a water body usually indicates good water quality.

Economic Importance for Humans: Negative

There are no significant negative impacts of mussels on humans.

Conservation Status

Fusconaia flava currently does not have any conservation status.

Additional Links

Encyclopedia of Life

Contributors

Renee Sherman Mulcrone (author).

References

Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. J. Exp. Zool. , 33: 463-499.

Brusca, R., G. Brusca. 2003. Invertebrates . Sunderland, Massachusetts: Sinauer Associates, Inc..

Burch, J. 1975. Freshwater unionacean clams (Mollusca: Pelecypoda) of North America . Hamburg, Michigan: Malacological Publications.

Cummings, K., G. Watters. 2004. "Mussel/Host Data Base" (On-line). Molluscs Division of the Museum of Biological Diversity at the Ohio State University. Accessed September 26, 2005 at http://128.146.250.63/Musselhost .

Cummings, K., C. Mayer. 1992. Field guide to freshwater mussels of the Midwest . Champaign, Illinois: Illinois Natural History Survey Manual 5. Accessed August 25, 2005 at http://www.inhs.uiuc.edu/cbd/collections/mollusk/fieldguide.html .

Lefevre, G., W. Curtis. 1912. Experiments in the artificial propagation of fresh-water mussels. Proc. Internat. Fishery Congress, Washington. Bull. Bur. Fisheries , 28: 617-626.

Lefevre, G., W. Curtis. 1910. Reproduction and parasitism in the Unionidae. J. Expt. Biol. , 9: 79-115.

Meglitsch, P., F. Schram. 1991. Invertebrate Zoology, Third Edition . New York, NY: Oxford University Press, Inc.

Mulcrone, R. 2004. Incorporating habitat characteristics and fish hosts to predict freshwater mussel (Bivalvia: Unionidae) distributions in the Lake Erie drainage, southeastern Michigan. Ph. D. Dissertation, University of Michigan, Ann Arbor, Michigan: 139 pp..

O'Dee, S., G. Watters. 2000. New or confirmed host identifications for ten freshwater mussels. Freshwater Mollusk Symposium Proceedings, Ohio Biological Survey, Columbus: 77-82.

Oesch, R. 1984. Missouri naiades, a guide to the mussels of Missouri . Jefferson City, Missouri: Missouri Department of Conservation.

Watters, G. 1995. A guide to the freshwater mussels of Ohio . Columbus, Ohio: Ohio Department of Natural Resources.

van der Schalie, H. 1938. The naiad fauna of the Huron River, in southeastern Michigan. Miscellaneous Publications of the Museum of Zoology, University of Michigan , 40: 1-83.