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