We adopted X-ray microtomography images and the specially designed algorithm that mimics the movement of spherical object in the shell channel to compare apertural barriers of two closely related clausiliid species with well documented reproductive strategies. For oviparous Laciniaria plicata, the patency of the shell channel was 0.60 mm (SD 0.09) at the ultimate whorl; 18.0% in relation to shell width. For viviparous Alinda biplicata, the patency of the shell channel was 1.24 mm (SD 0.06) at the ultimate whorl; 31.8% in relation to shell width. In the studied species, the patency of the shell channel differs significantly at the ultimate whorl, while at the penultimate whorl it is in both cases close to 43%. The technique applied in this study can be useful for analysing apertural patency in any gastropod species that develops a complex protective shell armature.