Oocyte size (in µm) distribution of two gastropod species from hydrothermal vent (Protolira valvatoides and Pseudorimula midatlantica) on different sites of the Montségur edifice (Lucky Strike vent field, Mid-Atlantic ridge). Data were collected thanks to histological analyses on several individuals of each species. Size structure of populations (shell length in mm) on different sites of the Montségur edifice.