Aquatic Species at Risk – Lilliput
SARA Status: Under consideration
COSEWIC Status: Endangered
Did You Know?
Lilliput can be hermaphroditic (each mussel features both male and female gonads) and like most other freshwater mussels, its larvae (glochidia) are parasitic on fishes.
In this case, adult mussels lure in a fish with worm-like filaments on their shells and release mucous packages of glochidia disguised as food. When the fish takes a bite, the package ruptures, releasing the glochidia to attach to their host as they flow through its gills. Here they will remain until they reach their juvenile, free-living stage and drop off to burrow in the substrate below.
The Lilliput resembles both the Rayed Bean (Villosa fabalis) and the Salamander Mussel (Simpsonaias ambigua), though the Rayed Bean has more prominent rays and a thicker hinge line, while the Salamander Mussel’s shell is thinner and more elongated.
The Lilliput (Toxolasma parvum) is one of Canada’s 54 freshwater mussel species. It is a rare and small mussel, typically less than 4 cm and occasionally reaching sizes of 5.5 cm in length. It is the only mussel of the genus Toxolasma found in Canada and can be recognized by the following features:
- thick shell that is elliptical to oval in shape;
- dull, smooth and cloth-like outer shell;
- front (anterior) end is rounded and the back (posterior) end is rounded on males, squared on females;
- shell colour is brown to brownish-black and may have green rays on the dorsal slope;
- inside of shell (nacre) is shiny and silvery-white or bluish-white;
- raised part at the top of the shell (beak) is sculptured with 4–6 heavy concentric ridges, and is slightly raised above the hinge line; and
- hinge teeth are fully developed, but compressed (thin serrated pseudocardinal teeth and long, thin and straight lateral teeth).
Lilliput is only found in North America, where it is widely distributed from the Gulf of Mexico to the Great Lakes basin. In Canada, Lilliput was historically found in southern Ontario in the drainages of lakes St. Clair, Erie and Ontario. No longer found in over 40 per cent of its historical range, Lilliput is now restricted to the Sydenham River, lower Thames River (Baptiste Creek), Ruscom River, Belle River, Grand River, Welland River, Jordan Harbour and Hamilton Harbour (Sunfish Pond, Cootes Paradise and Grindstone Creek).
In the United States, Lilliput can still found in 22 states, but is considered possibly extirpated from Georgia and New York, critically imperiled in Pennsylvania, endangered in Michigan, and vulnerable in Indiana and Wisconsin.
Lilliput is found in a variety of habitats, from small to large rivers to wetlands and the shallows of lakes, ponds and reservoirs. It prefers to burrow in soft substrates (river and lake bottoms) made of mud, sand, silt or fine gravel.
Lilliput has a short lifespan, living to a maximum age of 12 years. It can be hermaphroditic (each mussel features both male and female gonads). Spawning occurs from June to August and glochidia (mussel larvae) are released in July of the following year. Like most other freshwater mussels, the glochidia are parasitic on fishes. In this case, adult mussels lure in a fish with worm-like filaments on their shells and release mucous packages of glochidia disguised as food. When the fish takes a bite, the package ruptures, releasing the glochidia to attach to their host as they flow through its gills. Here they will remain until they reach their juvenile, free-living stage and drop off to burrow in the substrate below. Adult Lilliput essentially stays in one location (i.e. sessile), and may move only a few metres along the substrate the entire rest of its life. The likely host fishes for this mussel in Canada are the Johnny Darter (Etheostoma nigrum), Green Sunfish (Lepomis cyanellus) and Bluegill (Lepomis macrochirus). Like all species of freshwater mussels, Lilliput filters its food from the water. Bacteria and algae are its primary food sources.
Serious threats facing remaining Lilliput include habitat loss and the increasing pollution of the waters where they live and feed. Municipal, agricultural and industrial activities can result in higher levels of sediment, nutrients and contaminants that clog mussel gills, disrupt breathing, movement and reproduction, and degrade habitat quality. Other possible threats include habitat destruction, and even mussel removal, by riverbed dredging for transportation and shipping purposes, as well as continued residential and commercial development and dam construction along Lilliput habitat. Invasive Zebra and Quagga mussels can colonize on the Lilliput in large numbers, restricting their feeding, breathing, moving and reproduction. The invasive Round Goby may also out-compete the Lilliput for prey, as well as competing with its host fishes.
COSEWIC Assessment and Status Report on Lilliput, Toxolasma parvum, in Canada, 2013 ; Metcalfe-Smith et al. Photo Field Guide to the Freshwater Mussels of Ontario, 2005.
For more information, visit the SARA Registry.
Scientific name: Toxolasma parvum
SARA Status: Under consideration
COSEWIC Status: Endangered (May 2013)
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