The report covers a detailed study of the morphology and ecological distribution of 11 species in 9 genera of gammarid amphipods collected offshore in the eastern Gulf of Mexico. It is based upon large series of specimens of all ages obtained during a study of biofouling conducted off Panama City, Florida. A new species is noted in the genus Microjassa (description to be published elsewhere), and a second species, in the genus Stenothoe, appears to be undescribed, but confirmation awaits further literature study in an obscure journal. Additional contributions of this study are insights into the range of morphological variation displayed by individuals of a single species from one locale, a delineation of the development of certain secondary sexual characteristics that have been a source of confusion in the literature, an outline of the development of gammarid populations on virgin surfaces, and the impact of certain physical factors on the life cycles of selected species. (Author).