Morphometric variation and bilateral symmetry in a mangrove crab <i>Parasesarma eumolpe</i> (De Man, 1895) (Decapoda: Brachyura: Sesarmidae) from the Mekong Delta, Vietnam

Abstract Mangrove ecosystems in the Mekong Delta support a diverse array of brachyuran crabs, including sesarmids, which play key roles in leaf-litter processing and nutrient cycling. We quantified morphometric variation and bilateral symmetry in a mangrove crab Parasesarma eumolpe (De Man, 1895) collected from two mangrove forests in the Mekong Delta between August and October 2025. Measurements of carapace size and multiple appendage traits were obtained from both sides of the body to assess patterns of size-related variation and symmetry. Bilateral symmetry was generally not influenced by sex, whereas sampling site influenced bilateral symmetry for several traits, and body size contributed to symmetry variation in selected components. By contrast, sex (sexual dimorphism), sampling site, and body size explained variation in most absolute morphometric traits, with males larger than females and individuals from the Ca Mau mangrove forest generally larger than those from Can Tho. Strong positive relationships among chela components suggested coordinated, size-dependent growth. These results suggest that morphological variation in P. eumolpe may be shaped by the combined effects of sexual dimorphism, size-dependent growth, and ecological differences between mangrove habitats. Together, these findings provide baseline morphometric information for P. eumolpe and support comparative studies on morphometric variation and bilateral symmetry in mangrove-crab populations from the Mekong Delta. Our results provide a morphological baseline for future comparative, ecological, and taxonomic investigations of sesarmid and other mangrove-associated crabs in Southeast Asia.