By Renee Sherman Mulcrone
Geographic Range
Pyganodon lacustris is found in the St. Lawrence drainages, upper Susquehanna and Hudson, upper Mississippi, and southern Hudson Bay drainages of North America.
In Michigan, specimens have been collected from lakes in the northern part of the lower peninsula. (Hoeh and Burch, 1989)
Habitat
Pyganodon lacustris is mainly found in lakes, and seldom in rivers. Substrates where it is found include mud bottoms. (Hoeh and Burch, 1989)
These animals are found in the following types of habitat:
freshwater 
.
Aquatic Biomes:
rivers and streams.
Physical Description
(7.87 in)
Pyganodon lacustris is up to about 20 cm (8 inches) long , and is long-ovate or elliptical in shape. The shell is usually fairly thin and inflated. The anterior end is rounded, the posterior end is elongate, pointed and biangulate. The dorsal margin is straight, slightly sloping at each end, and the ventral margin is slightly rounded.
Umbos are full and low, being raised only slightly above the hinge line, and situated toward the anterior end of the shell. The beak sculpture consists of 4-5 irregularly looped bars.
The periostracum (outer shell layer) is yellow to yellow-olive with faint rays.
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 shallow. The nacre is bluish-white or reddish brown and iridescent.
In Michigan, this species can be confused with the giant floater. In general, Pyganodon lacustris is more elongate. (Hoeh and Burch, 1989)
Some key 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. (Arey, 1921; Lefevre and Curtis, 1910)
Special features of growth:
metamorphosis .
Reproduction
This species breeds once in the warmer months of the year.
In Michigan, the breeding season is probably in the summer months.
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.
Pyganodon lacustris is likely a long-term brooder and spawns in summer in Michigan. (Lefevre and Curtis, 1912; Watters, 1995)
Key reproductive features:
seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (internal ); 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. (Oesch, 1984)
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 Pyganodon lacustris attracts 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. (Arey, 1921; Brusca and Brusca, 2003; Watters, 1995)
Communicates with:
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. (Arey, 1921; Meglitsch and Schram, 1991; Watters, 1995)
Primary Diet:
planktivore ; detritivore .
Plant Foods:
algae; phytoplankton .
Other Foods:
detritus ; microbes.
Foraging Behaviors:
filter-feeding .
Predation
- muskrat, Ondatra zibethicus
- mink, Neovison vison
- raccoon Procyon lotor
- otter, Lontra canadensis
- turtles, Testudines
- hellbenders, Cryptobranchus
- freshwater drum, Aplodinotus grunniens
- sheepshead, Archosargus probatocephalus
- lake sturgeon, Acipenser fulvescens
- shortnosed sturgeon, Acipenser brevirostrum
- spotted suckers, Minytrema melanops
- common red-horse, Moxostoma
- catfish, Siluriformes
- pumpkinseed, Lepomis gibbosus
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. (Cummings and Mayer, 1992; Watters, 1995)
Ecosystem Roles
While freshwater mussels require a host fish for metamorphosis, the hosts for Pyganodon lacustris are unknown.
Key ways these animals impact their ecosystem:
parasite .
Economic Importance for Humans: Negative
There are no significant negative impacts of mussels on humans.
Economic Importance for Humans: Positive
Mussels are ecological indicators. Their presence in a water body usually indicates good water quality.
Conservation Status
Pyganodon lacustris is not listed in Michigan or any other states.
Other Comments
Little is known about the distribution or habitat of this species. Many specimens may have been identified as Pyganodon grandis. Molecular studies recently supported the status of this species. (Hoeh and Burch, 1989)
For More Information
Find Pyganodon lacustris information at
Contributors
Renee Sherman Mulcrone (author).
