Morphological variations in relation to sex and habitat in southern Mexico populations of the longarm river prawn Macrobrachium tenellum (Smith, 1871) (Decapoda: Caridea: Palaemonidae).

This article focuses on the morphological variation and sexual dimorphism of the longarm river prawn, *Macrobrachium tenellum*, an amphidromous species inhabiting rivers, estuaries, and coastal lagoons along the Pacific coast of the Western Hemisphere. Using geometric morphometrics, the study found significant differences in the size and shape of the carapace and second pleonal pleuron between males and females, with males generally larger and exhibiting distinct secondary sexual characteristics. Among females, three distinct ecophenotypes corresponding to river, estuary, and lagoon habitats were identified, likely reflecting adaptations to differing hydrodynamics, substrates, and environmental conditions. These findings contribute to understanding how habitat influences morphological traits in *M. tenellum*, with implications for species ecology, fisheries management, and aquaculture potential.