The pistolgrip, Tritogonia verrucosa, is a freshwater mussel found in rivers throughout the central and southeast United States. Its shape and surface texture set it apart from most other mussels. One of the most studied aspects of pistolgrip biology is its larval parasitism of fish hosts, which is necessary for it to reach its adult form and acts as a means of geographic dispersal. It has acquired a number of adaptations over its evolutionary history to aid in this parasitism.