Figure 2

Representative images (A-C) of the hydrobiid snail, Mexipyrgus churinceanus, collected from nearby populations to illustrate small scale variation in size and shell pigmentation. Herichthys minckleyi papilliforms (right figure D) exhibit gill arches modified into more gracile pharyngeal jaws with small muscles and pointed teeth that are ineffective at crushing snails while H. minckleyi molariforms (left figure D) have robust muscles and enlarged crushing teeth on their pharyngeal jaws that seem clearly modified to crush snails. Figure E portrays heterogeneity in habitats with Nymphaea (top) and without Nymphaea (bottom).