From the U.S. Fish and Wildlife Service's online digital media library.
Check http://images.fws.gov/ for higher quality version, and http://www.fws.gov/help/policies.html for copyright information.

Metadata
Title: Freshwater Mussel
Alternative Title: (none)
Creator: Engbretson, Eric
Source: WO-Engbretson-5742
Publisher: U.S. Fish and Wildlife Service
Contributor: DIVISION OF PUBLIC AFFAIRS
Language: EN - ENGLISH
Rights: (public domain)
Audience: (general)
Subject: Engbretson, Mussels
Date Issued: May 04 2004