Epioblasma torulosa rangiana
Northern riffleshell

Key Characteristics

The northern riffleshell is a medium sized (to 2 inches) mussel with a shell that is ovate to quadrate in shape becoming thicker anteriorly. There is considerable sexual dimorphism in riffleshell. Male shells have a sulcus or ridge running posterio-ventrally from just below the beak, whereas the female shells have a low bulge along the posterio-ventral edge of the shell that accommodates the enlarged marsupium containing eggs. The hinge teeth are medium-sized and well developed. The shell is light green-yellow to olive green, with dark, narrow, closely-spaced rays.

Status and Rank

  • State Status: E
  • US Status: LE
  • State Rank: S1
  • Global Rank: G2T2


County NameNumber of OccurrencesYear Last Observed
Distribution map for Epioblasma torulosa rangiana

Updated 5/15/2018. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.


Northern riffleshell occur in fine to coarse gravel areas of swift current riffle and runs.

Specific Habitat Needs

Rocky and sandy substrates needed in Mainstem Stream (3rd-4th order), Riffle, River (5th-6th order), Riffle

Natural Community Types


For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.


The future of the Northern riffleshell depends on the protection and preservation of habitat and host fish. Siltation and run-off must be reduced to facilitate the recovery of this species. Damming and dredging of rivers have had a negative effect on the riffleshell, altering fast flowing, clear water habitats and making them unsuitable for sustaining riffleshell populations. The continued spread of exotic species such as the zebra mussel throughout Great Lakes tributary rivers is a continuing and increasing threat to all native species. Control of zebra mussels is critical to preserving native mussels. And as with all mussels, protection of their hosts habitat is also crucial. Transplantation of viable populations into more protected and preserved habitats may be required to insure the long-term viability of this species.

Survey Methods

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at http://mnfi.anr.msu.edu/explorer [Accessed Sep 23, 2018]

More Information

See MNFI Species Abstract


Survey References

Technical References

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