Geographic Range
The giant floater is a widespread species, found throughout te Mississippi and Missouri river drainages, the St. Lawrence drainage,, Gulf of Mexico through Louisiana and Texas. In Canada it is in the Interior basin from western Ontario to Alberta.
In Michigan,
P. grandis
is found throughout streams, lakes and rivers in the state. In general, it is more
common in lakes, but is widespread throughout river systems.
Habitat
The giant floater is found in all habitats, but mainly in lakes or slower moving waters,
including backwaters of streams, rivers, and impoundments. It can colonize newly
impounded streams. Generally, it is found in substrates of mud or sand, but can also
be found in gravel.
- Habitat Regions
- freshwater
- Aquatic Biomes
- rivers and streams
Physical Description
The giant floater is up to 25.4 cm (10 inches) long , and is
elliptical or elongated in shape. The shape often varies. The shell is usually fairly
thin and inflated. The
anterior end
is broadly rounded, the posterior end bluntly pointed. The dorsal hinge line is
slightly curved and the ventral margin is straight or slightly curved.
Umbos
are full, raised slightly above the hinge line and are situated slightly towards
the anterior part of the shell. The beak sculpture has three to five double-looped
ridges.
The periostracum (outer shell layer) is smooth, yellow to yellow-green with rays in younger individuals. Older specimens tend to be more brown.
On the inner shell, the
left valve
lacks
pseudocardinal and lateral teeth
. There is a slight thickening sometimes where the lateral tooth would be.
The beak cavity is broad and shallow. The nacre varies from silvery white, yellow, pink or copper.
In Michigan, this species can be confused with
Pyganodon lacustris
,
paper pondshell
,
creeper
, and
cylindrical papershell
.
Pyganodon lacustris
is generally more elongate. The paper pondshell has flattened umbos. The creeper
may have a slightly waved and thickened hinge. The cyclindrical papershell generally
has a beak sculpture of concentric, single loops.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
Development
Fertilized eggs are brooded in the marsupia (water tubes) up to 11 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
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.
In the Huron River in Michigan,
Pyganodon grandis
was gravid from early August to the following mid-April. It probably spawns from
May through July in Michigan.
- Key Reproductive Features
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- 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
-
provisioning
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.
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 giant floater attracts its fish hosts 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
- Perception Channels
- visual
- tactile
- vibrations
- 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
- detritivore
- Plant Foods
- algae
- phytoplankton
- Other Foods
- detritus
- microbes
- Foraging Behavior
- 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 metamorphosis 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.
Glochidial metamorphosis and natural infestations have been observed for bluegill , green sunfish , black crappie , rock bass , largemouth bass , bluntnose minnow , central stoneroller , common shiner , striped shiner , blackchin shiner , blacknose shiner , brook silverside , Iowa darter , Johnny darter , rainbow darter , and yellow perch .
In lab trials, glochidial metamorphosis was observed on
banded killifish
,
golden topminnow
,
longnose gar
,
longear sunfish
,
pumpkinseed
,
creek chub
,
golden shiner
,
redfin shiner
,
blacknose dace
, brook stickleback
- Ecosystem Impact
- parasite
- bluegill, Lepomis macrochirus
- green sunfish, Lepomis cyanellus
- black crappie, Pomoxis nigromaculatus
- rock bass, Ambloplites rupestris
- largemouth bass, Micropterus salmoides
- bluntnose minnow, Pimephales notatus
- central stoneroller, Campestoma anomalum
- common shiner, Luxilus cornutus
- striped shiner, Luxilus chrysocephalus
- blackchin shiner, Notropis heterodon
- blacknose shiner, Notropis heterolepis
- brook silverside, Labidesthes sicculus
- Iowa darter, Etheostoma exile
- Johnny darter, Etheostoma nigrum
- rainbow darter, Etheostoma caeruleum
- yellow perch, Perca flavescens
- banded killifish, Fundulus diaphanus
- golden topminnow, Fundulus chrysotus
- longnose gar, Lepisosteus osseus
- longear sunfish, Lepomis megalotis
- pumpkinseed, Lepomis gibbosus
- creek chub, Semotilus atromaculatus
- golden shiner, Notemigonus crysoleucas
- redfin shiner, Lythrurus umbratilis
- blacknose dace, Rhinichthys atratulus
- brook stickleback, Culaea inconstans
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
Pyganodon grandis
is fairly common throughout its range. However, it is considered Threatened in Vermont.
Other Comments
The genus
Anodonta
is synonomous with
Pyganodon
. Because of the variation in shell morphology,
Pyganodon grandis
was once considered to be several species.
Additional Links
Contributors
Renee Sherman Mulcrone (author).
- Nearctic
-
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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- freshwater
-
mainly lives in water that is not salty.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- heterothermic
-
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.
- bilateral symmetry
-
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.
- metamorphosis
-
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.
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- external fertilization
-
fertilization takes place outside the female's body
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- chemical
-
uses smells or other chemicals to communicate
- phytoplankton
-
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
- detritus
-
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
- filter-feeding
-
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.
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- planktivore
-
an animal that mainly eats plankton
- detritivore
-
an animal that mainly eats decomposed plants and/or animals
References
Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. J. Exp. Zool. , 33: 463-499.
Arey, L. 1932. The formation and structure of the glochidial cyst. Biological Bulletin (Woods Hole) , 62: 212-221.
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., 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 .
Hoeh, W. 1990. Phylogenetic relationships among Eastern North American Anodonta (Bivalvia: Unionidae). Malacological Review , 23(1-2): 63-82.
Hove, M. 2004. "Links to each state's listed freshwater mussels, invertebrates, or fauna" (On-line). Accessed September 21, 2005 at http://www.fw.umn.edu/Personnel/staff/Hove/State.TE.mussels .
Howells, R. 1997. New fish hosts for nine freshwater mussels (Bivalvia: Unionidae) in Texas. Texas Journal of Science , 49: 255-258.
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.
Oesch, R. 1984. Missouri naiades, a guide to the mussels of Missouri . Jefferson City, Missouri: Missouri Department of Conservation.
Penn, G. 1939. A study of the life cycle of the freshwater mussel, Anodonta grandis, in New Orleans. Nautilus , 52: 99-101.
Trdan, R., W. Hoeh. 1982. Eurytopic host use by two congeneric species of freshwater mussel (Pelecypoda: Unionidae: Anodonta). American Midland Naturalist , 108: 381-388.
Tucker, M. 1928. Studies on the life cycles of two species of fresh-water mussels belonging to the genus Anodonta. Biological Bulletin (Woods Hole) , 54: 117-127.
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.