Baseline Morphometric Assessment and Sexual Dimorphism of Three Freshwater Mollusks in a Tropical Floodplain Wetland

This study examined the morphometric variability and sex-related patterns in three freshwater mollusk species, Pila globosa, Lamellidens marginalis, and Parreysia corrugata from the Hakaluki Haor ecosystem, Bangladesh. All species showed strong linear relationships between shell length and body weight (p < 0.001). The R2 values indicated moderate association in P. globosa (0.57) and L. marginalis (0.59) and a high association in P. corrugata (0.80). Most traits were similar across sexes; however, females of P. corrugata had significantly higher body weight and slightly wider shells, suggesting mild sexual dimorphism. Condition indices were species-specific, with males generally higher, notably in P. corrugata (p < 0.05). Violin box plots showed minor sex differences in P. globosa aperture and spire, with overlap. PCA revealed that size traits were major contributors, explaining 60–75% of the variation. Females of P. globosa scored higher on the size axis, indicating sexual size dimorphism, while L. marginalis and P. corrugata showed significant overlap. Overall, results highlight strong allometric scaling, limited species-specific sexual dimorphism, and body size as the main determinants of morphology.