A new species of the genus Gammarus (Crustacea: Amphipoda: Gammaridae) from the low salinity habitats in the northern Gulf of Mexico

In the northern Gulf of Mexico, Gammarus mucronatus sensu lato is represented by at least two forms, G. mucronatus sensu stricto and a less common “macromucronate” form, which appears to be restricted to low salinity habitats. These two forms have traditionally been separated using the size or angle of projection of the dorsal mucronations (processes). However, because of variability in the development of the processes, it is unclear whether this and other morphological differences between G. mucronatus sensu stricto and the “macromucronate” form are ecophenotypic or reflect distinct and separate species. Detailed morphological analyses indicate that these two forms represent distinct species; Gammarus lecroyae, new species, is described in detail and a key to the marine and estuarine Gammarus species from the northern Gulf of Mexico is provided.