The western Atlantic Ocean harbors a diverse fauna of squat lobsters, particularly in the family Munidopsidae. This study introduces Munidopsis sednasp. nov., a species only found in the Gulf of Mexico and the first species reported to be endemic to cold seeps in the western Atlantic. Our investigation incorporates morphological analyses including micro-CT scanning evidence, multilocus molecular phylogeny, and mtDNA phylogeography, as well as ecological data derived from in situ observations and geographic distribution patterns to substantiate the recognition of the new species. Shallow molecular divergences and multiple morphological differences differentiate the new species from its closest relative, M. longimanus (A. Milne-Edwards, 1880). Additionally, we explore the potential scenario for ecological speciation within this newly identified taxon and discuss its significance in the context of conservation efforts in the Gulf of Mexico.