Shell phenotype is the result of adaptive evolution in molluscs. In order to explore the specificity of shell phenotype and its relationship with eco-hydraulics, this study examined the shell-body mass ratio and the hydrostatic settling characteristics of nine mollusc species, as well as their interspecific differences and correlations. The results showed that body mass (C.V.=1.11) was the most significant morphological index, compared to shell length (C.V.=0.67) and shell width (C.V.=0.54). The shell-body mass ratio differed significantly between species (P < 0.01), however, with a small variation coefficient (C.V.=0.20). The average shell-body mass ratio was 0.32 ±0.13, and was significantly smaller in terrestrial molluscs than in aquatic molluscs (P < 0.01). The largest shell-body mass ratio was found in Corbicula fluminea (0.54±0.06), which was more than three times that of the smallest species, Achatina fulica (0.17±0.04). The shell mass of Pomacea canaliculata was half of its body mass (0.50±0.06). The settling behavior was significantly different between bivalves and snails. Cipangopaludina cathayensis, Bellamya aeruginosa, and C. fluminea were the only three species which could not float in still water, in the present study. The fastest settling velocity of C. fluminea ((24.99±4.22) cm/s) was nearly six times that of the slowest, Radix swinhoei ((4.13±0.96) cm/s). Settling velocity and settling acceleration did not differ significantly between the invasive snails A. fulica ((18.30±3.64) cm/s) and P. canaliculata ((21.77±5.23) cm/s), and the native snails B. aeruginosa ((19.48±3.14) cm/s) and C. cathayensis ((21.44±3.92 cm/s). Shell-body mass ratio was correlated with settling velocity (R²=0.28) and settling acceleration (R²=0.39) in adults. Following current research, the study of settling behavior changing with life history will further reveal the role of eco-hydraulics in evolution and population expansion in molluscs.