Much more of a snail can be observed if it is induced to extend fully. The simplest method is to place the shell in water with its aperture facing up. A brief glimpse of behind the head, where the penis is usually located on males, may be had as the snail stretches out to grip the substrate and turn the shell.
Full article of Anatomy of marine gastropods without dissection. below image 2 2 Gastropod anatomy. Transparent sole of Janolus hyalinus on undersurface of water.