Fat muckets ( (Burch, 1975)) are found in the Mississippi River drainage from New York to Minnesota. They occur south to Arkansas but do not occur in the Tennessee or Cumberland River systems. In the St. Lawrence River system, they are found in the Canadian Interior Basin. Fat muckets are also found in Montana and eastern Colorado. In Michigan, they are found in drainages throughout the state, both in the upper and lower peninsulas.
Although they may be found in various substrates and habitats, from lakes and headwaters to medium-sized rivers, fat muckets are usually found in quiet areas with sandy-mud substrates. Occasionally they are found in riffles, but more often they are found in the water below riffles, or in slowly running water with fine gravel, sand or mud substrates. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)
Fat muckets are up to 12.7 cm long, with an oblong to elliptical shape. Their shell thickness is uniform, and may be thin to thick. This species is sexually dimorphic. Depending on habitat, sex and age, the shell can be compressed or inflated. Their anterior end is rounded, while their posterior end is bluntly pointed in males and truncated in females. Their dorsal margin is straight and their ventral margin is straight or rounded. Their umbos are broad and raised only slightly above the hinge line. Their beak sculpture is fine, with six to ten double-loops. Their periostracum (outer shell layer) is yellow to yellow-brown with green rays. Older specimens tend to be darker and brownish. On the inner shell, their left valve has two pseudo cardinal teeth, which are erect and compressed. Their two lateral teeth are thin, short and slightly curved. Their right valve has one large, erect pseudo cardinal tooth. Anterior to this tooth is a smaller (lamellar) tooth. Their lateral tooth is thin and straight. Their beak cavity is shallow to moderately deep. Although the nacre is white, occasionally it is has a pink or salmon tint and is iridescent posteriorly. In Michigan, fat muckets may be confused with muckets and pocketbooks, although muckets are more compressed and slightly more elliptical and pocketbooks are rounder and have higher umbos. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)
Fertilized eggs are brooded in the marsupia (water tubes) up to 11 months, where they develop into larvae, called glochidia. The glochidia are released into the water where they 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. (Arey, 1921; Lefevre and Curtis, 1910)
Among unionids, gametogenesis is initiated by increasing water temperatures. Their life cycle includes open fertilization; males release sperm into the water, which is taken in by the females through their respiratory current. Eggs are fertilized internally in the suprabranchial chambers, and pass into water tubes of the gills, where they develop into glochidia. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)
The age at which fat muckets reach sexual maturity is unknown. Unionids are gonochoristic (sexes are separate) and viviparous. Glochidia, their larval stage, are released live after they are fully developed. Fat muckets are long-term brooders; in Michigan, they are gravid from early August to late July in the Huron River and probably breed in July and early August. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)
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. (Lefevre and Curtis, 1912; van der Schalie, 1938; Watters, 1995)
Their age can be determined by looking at the annual rings on their shell. However, no demographic data has been recorded on this species, although members of family Unionidae generally have about a 10 year lifespan. (Haag, 2012; Winhold, 2004)
In general, mussels are rather sedentary, although they may move in response to changing water levels and conditions. It is not thoroughly documented, but mussels may vertically migrate to release glochidia and spawn. Female fat muckets have a mantle flap that resembles a minnow or darter, which lures their host fishes, who chews on the flap and breaks the membrane of the gills. As a result, fishes are infected with glochidia. (Oesch, 1984)
There is currently no information available about the home range size of fat muckets.
Most bivalve sensory organs are located in the middle lobe of their mantle edge. The mussel’s foot includes paired statocysts, which are fluid filled chambers with a solid granule or pellet (a statolity). The statocysts help mussels with georeception and orientation. Mussels are heterothermic, and therefore sensitive and responsive to temperature. In general, unionids may have some form of chemical reception to recognize fish hosts. In genus Lampsilines, mantle flaps are modified to attract potential fish hosts. While fat muckets have a fish lure to attract host fishes, their method of recognition is unknown. Glochidia respond to touch, light and some chemical cues. In general, when touched or introduced to a fluid, they respond by clamping shut. (Arey, 1921; Brusca and Brusca, 2003; Watters, 1995)
In general, unionids are filter feeders. Mussels use cilia to pump water into their incurrent siphon where food is caught in a mucus lining in the demibranchs. Particles are sorted by their labial palps and are directed to their mouths. Mussels have been cultured on algae, but they may also ingest bacteria, protozoa 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 tissues through phagocytosis. (Arey, 1921; Meglitsch and Schram, 1991; Watters, 1995)
In general, unionids are preyed upon by muskrats, minks, North American river otters and some birds. Juveniles are probably also consumed by the following fish species: freshwater drums, sheepshead, lake sturgeon, spotted suckers, common redhorses and pumpkinseeds. (Cummings and Mayer, 1992; Watters, 1995)
Glochidia will attach to almost any fish, including those that are not suitable hosts. Fat muckets mainly use fish hosts from family Centrarchidae. Infestations and glochidial metamorphosis have been observed on bluegills, black crappies, largemouth bass, walleyes, white crappies and yellow perch. Glochidial metamorphosis has also been observed on longear sunfishes, bluntnose minnows, sand shiners, saugers and smallmouth bass. Their mortality and reproduction is affected by unionicolid mites and monogenic trematodes feeding on their gill and mantle tissues. Likewise, parasitic chironomid larvae may destroy up to half the mussels’ gill. (Coker, et al., 1921; Cummings and Mayer, 1992; Cummings and Watters, 2004; Howard, 1922; O'Dee and Watters, 2000; Trdan, 1981; Watters, 1995)
Mussels are ecological indicators. Their presence in a water body usually indicates good water quality. (Farris and Van Hassel, 2007)
There are no significant negative impacts of mussels on humans.
As of 2012, fat muckets were listed as a species of least concern according to the IUCN Red List of Threatened Species. (Cummings and Cordeiro, 2012)
Renee Sherman Mulcrone (author).
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
an animal that mainly eats decomposed plants and/or animals
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
fertilization takes place within the female's body
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
an animal that mainly eats plankton
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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