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Contact information
For information on Wisconsin's rare vertebrate animals, contact:
Rich Staffen
Conservation Biologist
For information on Wisconsin's rare invertebrates, contact:
Jay Watson
Conservation Biologist

Buckhorn (Tritogonia verrucosa)



Buckhorn (Tritogonia verrucosa), listed as Threatened in Wisconsin, is found in medium to large-sized rivers, with a moderate to swift current, and clean, firm substrates. The known host fish are yellow and brown bullheads and flathead catfish.

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

The table below provides information about the protected status - both state and federal - and the rank (S and G Ranks) for Buckhorn (Tritogonia verrucosa). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where occurrences of this species meet NHI data standards and is not meant as a comprehensive map of all observations.

Note: Species recently added to the NHI Working List may temporarily have blank occurrence maps.

Documented locations of Tritogonia verrucosa in the Natural Heritage Inventory Database as of July 2015.
Summary Information
State StatusTHR
Federal Status in Wisconsinnone
State RankS2
Global RankG4G5
Tracked by NHIY

Species guidance

Note: a species guidance document is not available at this time. Information below was compiled from publication PUB-ER-085-99 (now out-of-print).

Identification: The elongate shell is brown or black, moderately large, heavy, and has many pustules. Low umbo. Beak sculpture consisting of a series of ridges continuing down the side. Pseudocardinal teeth are heavy and serrated and the lateral teeth are long, straight and striated. Ventral margin usually arched. Beak cavity deep. The nacre is white and posteriorly iridescent. The female shell has larger wing-like extensions, which the males lack. Length to 8 inches (20.3 cm).

Habitat: Inhabits fairly deep water on a sand or mud bottom. Also found in riffles and in shallow water (1-3 m) of smaller streams.

State Distribution: Occurs in the following rivers: the Mississippi, the Black, the upper and lower Wisconsin, the White, the St. Croix, the Baraboo, the Chippewa, the Eau Claire, the Pecatonica, and the Wolf.

Phenology: The breeding season lasts from April to July. The brown bullhead (Ameiurus nebulosus), yellow bullhead (Ameiurus natalis), and flathead catfish (Pylodictis olivaris) are known hosts.

Management Guidelines: Habitat destruction and river pollution have resulted in mussel declines. Protection of habitat and improvements in water quality along with restriction of dredging, impoundments, sand and gravel mining, and navigational improvements would benefit this species. The development of fish runways to facilitate the movement of host species through or around dams could also help to protect this species.




Photo by Lisie Kitchell, WDNR.

Wildlife Action Plan

Wisconsin Wildlife Action Plan graphic

Natural community (habitat) associations

The table below lists the natural communities that are associated with Buckhorn. Only natural communities for which Buckhorn is "high" (score=3) or "moderate" (score=2) associated are shown. See the key to association scores for complete definitions. Please see the Wildlife Action Plan to learn how this information was developed.

Natural community Score
Warmwater rivers 3
Warmwater streams 3

Ecological landscape associations

The table below lists the ecological landscape association scores for Buckhorn. The scores correspond to the map (3=High, 2=Moderate, 1=Low, 0=None). For more information, please see the Wildlife Action Plan.

This map shows the probability of Buckhorn occurring in each of Wisconsin's Ecological Landscapes.  Actual scores can be found in the table to the left.

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Landscape-Community combinations of highest ecological priority*

Ecological priorities are the combinations of natural communities and ecological landscapes that provide Wisconsin's best opportunities to conserve important habitats for a given Species of Greatest Conservation Need. The 10 highest scoring combinations are considered ecological priorities and are listed below. More than 10 combinations are listed if multiple combinations tied for 10th place. For more information, please see the Wildlife Action Plan.

* Ecological priority score is a relative measure that is not meant for comparison between species. This score does not consider socio-economical factors that may dictate protection and/or management priorities differently than those determined solely by ecological analysis. Further, a low ecological priority score does not imply that management or preservation should not occur on a site if there are important reasons for doing so locally.

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Issues/threats and conservation actions

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for rare animals

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Last revised: Thursday, December 22, 2022