Several years ago for a period of more than a year, I kept several live Rumina saharica, the smaller relative of the better known land snail Rumina decollata (actually, neither species is that well known). I had kept copious notes and took some photographs. So, recently I decided that I had enough data for a short paper and started working on it.
One activity that I was lucky enough to witness and photograph was R. saharica's mating.
In fact, I observed 2 pairs mating simultaneously next to each other. When I took this photograph, one pair had separated, but one snail (on the left) still had its penis everted (white arrow). The pair on the bottom was still mating. Their mating position is interesting: one snail lies on its side, while the other, also on its side, stretches its head over that of the lower snail. As far as I can tell, each snail inserts its penis into its mate's genital opening (red arrow).
Rumina decollata is known to be a facultative selfer, that is, it can reproduce without mating (Selander et al. 1974. Self-fertilization in the terrestrial snail Rumina decollata. Veliger 16: 265). Can R. saharica also reproduce without mating? You have to wait for my paper to learn the answer.