Alpheus cristulifrons is a snapping shrimp that commonly lives in male-female pairs in crevices and cavities in and around coral reefs. Relatively common and widespread, this species ranges from Florida south to Brazil. Snapping shrimp in the genus Alpheus-- including A. cristulifrons-- have been a model system for studying molecular divergence in "transisthmian" taxa that diverged following the closure of the Isthmus of Panama (Knowlton et al. 1993, Hurt et al. 2009). For more details, see Knowlton et al. (2008): http://biogeodb.stri.si.edu/bioinformatics/alpheus/Alpheus_Template.php?species=cristulifrons.