Snuffbox (Epioblasma triquetra)


Top facts

  • Freshwater mussels are among the world’s most imperilled animals and population declines have been reported globally.
  • It is thought that the invertebrates_freshwater’s range was previously 60 percent larger than it is currently.
  • The larvae of the snuffbox undergo a period of parasitism on a host fish while developing into adults.
  • One reason for the dramatic decline of the snuffbox is the invasive zebra mussel.
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Snuffbox fact file

Snuffbox description

GenusEpioblasma (1)

The invertebrates_freshwater (Epioblasma triquetra) is a small- to medium-sized freshwater mussel. The shell of this species is solid and smooth with the exception of radial, wavy ridges on the surface (3). The shell of the male is triangular, whereas the female’s shell is slightly elongated (3) (4). The shell is yellow, green, or brown and is marked with numerous green rays, blotches, or chevron-shaped lines (2) (4) (5). As the snuffbox ages, the shell becomes darker and the markings are less distinct (2). The inside of this mussel’s shell, known as the ‘nacre’, is iridescent and pearly (4).

Also known as
épioblasme tricorne.
Dysnomia triquetra.
Male shell length: up to 7.1 cm (2)
Female shell length: up to 4.5 cm (2)

Snuffbox biology

As a suspension feeder, the invertebrates_freshwater pumps water through its body using small hair-like structures to filter out the particulate matter that it feeds on (2) which consists of algae, bacteria, microscopic animals, or detritus (2).

The snuffbox reproduces similarly to many other mussel species. In summer, the male releases sperm into the water column, which the female filters with its gills. Fertilisation takes place on the gills (3) and the young are released the following summer (5). The snuffbox belongs to the Order Unionoida, and all species in this Order have somewhat unusual juvenile life forms (3). After being released from the gills of the female, the larvae of the snuffbox, known as ‘glochidia’, must parasitise a host fish in order to develop into the adult form (3). The snuffbox glochidum has hooks which it uses to cling onto the gills of a suitable host fish, and becomes enclosed in a cyst parasitising the fish (3). After a few weeks the parasitic glochidia fall from the host fish into the substrate, where they develop into an adult (6). As this species is incapable of moving long distances, the temporary parasitic life stage provides it with a vital dispersal method (3). Until recently the blackside darter (Percina maculata) and logperch (Percina caprodes) were considered the only possible host fish species (3), although recent experiments have shown that the Iowa darter (Etheostoma exile), rainbow darter (Etheostoma caeruleum), mottled sculpin (Cottus bairdii), Ozark sculpin (Cottus hypselurus), and largemouth bass (Micropterus salmoides) may also be hosts (3) (4).

Many of the snuffbox’s close relatives have an array of lures, baits and behaviours to attract host fish for their glochidia, but the snuffbox is known to clamp onto the head of the logperch and pump glochidia into the fish’s mouth and gills. Unlike other relatively harmless mussel-fish interactions, the snuffbox occasionally kills the potential host, but the logperch has a reinforced snout and usually survives the encounter (6).

The snuffbox, along with other North American freshwater mussels, is preyed on by muskrats (Ondatra zibethicus), racoons (Procyon lotor), American mink (Neovison vison), North American river otters (Lontra canadensis), and some birds (3).


Snuffbox range

The invertebrates_freshwater is endemic to the waterways of North America, especially those on the east coast between Wisconsin and Alabama, and is also found in Ontario in Canada (3) (4). It is thought that the snuffbox’s range used to be 60 percent larger than it is now (4) (5).


Snuffbox habitat

The snuffbox is found in the riffle areas of fast-moving rivers and streams (3). It is generally found at depths between 0.5 and 2.5 metres (3), and usually buries itself in the substrate, which may be sand, gravel or stone (2).


Snuffbox status

The snuffbox has not yet been assessed by the IUCN.


Snuffbox threats

Freshwater mussels are among the world’s most imperilled animals and population declines have been reported globally (3). The Unionida populations of North America have experienced dramatic reductions in size, with around 70 percent of approximately 300 freshwater mussel species in decline and many now considered rare, endangered, and threatened (3). It is estimated that this species is only present in 40 percent of its historical range, and the populations that remain are fragmented. This species is likely to be locally extinct in Iowa, Kansas, New York, and Mississippi (3). Although it is not now thought to constitute a major threat to this species, the overcollection of mussels for the button industry may have been the cause of many population declines (3).

One reason for the dramatic decline of the invertebrates_freshwater is the invasive zebra mussel (Dreissena polymorpha), which attaches to the shells of native mussels and can interfere with respiration, feeding, movement, and excretion (3). Another invasive species, the round goby (Neogobius melanostomus), may also threaten the snuffbox by displacing host fish, thereby reducing the likelihood of reproduction and the capacity for dispersal, particularly in an upstream direction (2). In Canadian populations, another invasive species, the common carp (Cyprinus carpio), is a threat to this species as it predates the juveniles, uproots plants, and feeds on sediment-associated fauna, which can increase turbidity and sedimentation (3), reducing the suitability of the habitat and even causing mussels to suffocate (2). Sedimentation can also be accelerated within the habitat of the snuffbox by intensive timber harvesting, heavy recreational use, and poor land use practices (2) and these actions are thought to be the primary limiting factor for most species in the Sydenham and Ausable Rivers in Canada (3).

The construction of dams is likely to affect both upstream and downstream mussel populations, by changing water temperatures, disrupting river flow patterns, scouring river bottoms and eliminating suitable habitats (2). Dams also prevent the movement of host fish in rivers, which limits the dispersal of the snuffbox and effectively isolates upstream and downstream populations (2).

The leaching of fertilisers, herbicides, and pesticides into the habitat of the snuffbox is likely to be a threat to this species and its habitat, as well as contamination from oil, grease and heavy metals which can enter aquatic areas from nearby roads (3).  This pollution may directly affect the snuffbox, as well as indirectly threaten this species by reducing host fish populations, thereby reducing the chances of successful reproduction.


Snuffbox conservation

The invertebrates_freshwater is classified as endangered in the United States (7) and in Canada (3) which protects this species by prohibiting its collection or purposeful mortality. An in-depth species recovery plan was written in 2006, laying out plans for conservation measures to protect five species of freshwater mussel in Canadian rivers (3). The recovery plan includes several steps, such as determining the extent and populations of host fish, defining the specific habitat requirements of the snuffbox, monitoring the population, identifying and evaluating threats, remediating threats, and examining the feasibility of relocations (3).

There are a number of non-specific conservation measures to increase the quality of waterways in Canada, including the Walpole Island Ecosystem Recovery Strategy (8) which may benefit many species through an overall improvement of the aquatic environment (3). Further research into the life history and population dynamics of the snuffbox may assist in the design of more species-specific conservation measures. A quantitative assessment of the risks and the success of conservation actions may be possible if a scheme of long-term monitoring of abundance and distribution is undertaken (3).


Find out more

Find out more about freshwater mussels in the Order Unionoida:

Read more about mussel conservation in North America:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
Litter formed from fragments of dead material.
A species or taxonomic group that is only found in one particular country or geographic area.
The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
Describes species introduced deliberately or unintentionally outside their natural habitats where they have the ability to establish themselves, invade, outcompete natives and take over the new environments.
Of or relating to the immature stage in an animal’s lifecycle, after it hatches from an egg and before it changes into the adult form. Larvae are typically very different in appearance to adults; they are able to feed and move around but are usually unable to reproduce.
A category used in taxonomy, which is below ‘class’ and above ‘family’. All members of an order have characteristics in common.
Describes an organism that derives its food from, and lives in or on, another living organism at the host’s expense.
Light rapids where water flows across a shallow section of river.


  1. Catalogue of Life (April, 2014)
  2. United States Department of Agriculture: Natural Resources Conservation Service - Snuffbox (April, 2014)
  3. Morris, T. J. and Burridge, M. (2006) Recovery Strategy for Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed Bean in Canada. Species at Risk Act Recovery Strategy Series. Fisheries and Oceans Canada, Ottawa. Available at:
  4. NatureServe Explorer - Epioblasma triquetra (April, 2014)
  5. United States Forest Service Conservation Assessment - The Snuffbox (April, 2014)
  6. Missouri State University Unio Gallery - Epioblasma (April, 2014)
  7. United States Fish and Wildlife Service Species Profile - Snuffbox mussel (April, 2014)
  8. Bowles, J.M. (2005) Walpole Island Ecosystem Recovery Strategy. Walpole Island Heritage Centre, Environment Canada and The Walpole Island Recovery Team, Ontario, Canada. Available at:

Image credit


© Corey Raimond

Corey Raimond


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