Missouri Department of Conservation
Home » Discover Nature » Field Guide

Sheepnose (Bullhead)

1 of 2
1 of 2
Plethobasus cyphyus
Family: 
Unionidae (freshwater mussels) in the phylum Mollusca
Description: 

Shell thick, oval or oblong, somewhat elongate, and slightly inflated. Anterior end rounded; posterior end bluntly pointed. Dorsal margin straight, ventral margin curved anteriorly, straight posteriorly. Umbos slightly elevated above hinge line. Beak sculpture of two heavy ridges, visible only in young shells. Shell smooth, except for a row of knobs or tubercles on center of valve, running from umbo to ventral margin. A shallow sulcus (furrow) is present between row of tubercles and posterior ridge. Epidermis yellow or light brown in juveniles, becoming chestnut to dark brown in adults.

Pseudocardinal teeth small relative to overall shell size; two in left valve, one in right (with occasional smaller tubercular tooth on either side). Lateral teeth long, straight or slightly curved; two in left valve, one in right. Beak cavity shallow. Nacre white, occasionally tinged with pink or salmon.

Similar species: White wartyback, threehorn wartyback, round pigtoe, Wabash pigtoe.

Size: 
Adult length: up to 5 inches.
Habitat and conservation: 
Found in medium to large rivers, with a moderate to swift current, with gravel or mixed sand and gravel substrate.
Foods: 
Algae and fine particles of decaying organic matter; extracts nutrients and oxygen from water drawn into the body cavity through a specialized gill called the incurrent siphon; sediment and undigested waste are expelled through the excurrent siphon.
Distribution in Missouri: 
Found only in the east-central part of Missouri, primarily in the Meramec River basin.
Status: 
Endangered in Missouri; candidate for federal Endangered status.
Life cycle: 
Males release sperm directly into water. Females downstream siphon sperm into the gill chamber, where eggs are fertilized. Eggs mature into larvae (called glochidia), which discharge into the water and attach to host fish—in this species, apparently the sauger. The tiny mussel eventually breaks away and floats to the bottom of the stream, and the cycle repeats.
Human connections: 
Mussels are excellent biological indicators of water quality because they are long-lived and relatively immobile, accumulating contaminants in water that can be scientifically analyzed. Because of its particularly hard nacre, this shell was not used in the commercial button industry.
Ecosystem connections: 
Mussels act as nature's “vacuum cleaners,” filtering and cleansing polluted waters. They are also an important food source for other species in the aquatic environment.

Other Content You May Like

  • Scaleshell

    Rarely seen, this Endangered freshwater mussel has a thin and delicate shell that is strikingly beautiful inside.

  • Snuffbox

    The snuffbox has been classified as Endangered in Missouri and is a candidate for federal Endangered status. Perhaps it should also be a candidate for a new common name, since the popularity of snuff-taking is long past.

  • Spectaclecase (Spectacle Case)

    Missouri may have the largest number of spectaclecase mussels left in the world. These elongated shellfish can live for 60 years or more.

  • Wartyback

    This favored habitat of this vulnerable species is large streams or rivers in firm sand and mud. The bumps on the shell may help to anchor it in the river bottom.

  • Elephantear (Elephant's Ear)

    Today found only in the Meramec River, the elephantear has been classified as Endangered in Missouri and is a candidate for federal Endangered status.

  • Pink Mucket

    This endangered native mussel lives in flowing waters of large streams among gravel and cobble.

  • Ebonyshell

    At one time the most valuable shell to the commercial button industry, the ebonyshell is now classified as Endangered in Missouri and is a candidate for federal Endangered status.

MDC's Mission, Vision, Priorities

MDC protects and manages Missouri's fish, forest, and wildlife resources.

We also facilitate your participation in resource-management activities, and we provide opportunities for you to use, enjoy and learn about nature.

Find out more

Burr Oak Woods Nature Center
Shortened URL
http://mdc.mo.gov/node/6582
Serving Nature and You

MDC protects and manages Missouri's fish, forest, and wildlife resources.
We also facilitate your participation in resource-management activities, and we provide opportunities for you to use, enjoy and learn about nature.

Featured Pic

Check out the featured picture and other images at the MDC Media Gallery

Visit the media gallery
Popular Topics

Follow MDC on Twitter Facebook YouTube Flickr Pinterest Slideshare MDC RSS feeds

© 2013 Conservation Commission of Missouri. All rights reserved.