Two new species of commensal leucothoid amphipods, Leucothoe ashleyae and Leucothoe kensleyi, are described with detailed host and ecological data. Although leucothoid amphipods are common endocommensals in sponges, tunicates, and bivalve mollusks, few authors have detailed specific host associations. Information on specific leucothoid host associations will further refine taxonomic and ecological studies within Leucothoidae. The convoluted taxonomic history of leucothoids necessitates the development and application of more precise taxonomic methodologies to enable comparative analyses among taxa. Persistent taxonomic constraints within Leucothoidae [sensu lato] include numerous cryptic species groups, most notably the problematic Leucothoe spinicarpa “complex.”