Many species of fungi are obligate associates of arthropod hosts (Mattson 1988). Fungi belonging to the genera Enterobryus and Taeniella have been discovered in the hindgut of U. rapax. These species are not parasitic (Hibbits 1978, Lichtwardt 1976), and it has been suggested that they may even provide necessary chemical compounds, such as amino acids, to the crab (Williams & Lichtwardt 1972). In addition to obligate associations, mudflat fiddler crabs are found alongside several organisms common to mangroves and salt marshes. For extensive lists of other species found throughout the ecosystems in which U. rapax occurs, please refer to the "Habitats of the IRL" link at the left of this page.