@alex @dantheclamman Even better:

"In some species of marine slugs (Onchidium), individual animals possess two eye types. The first type is a pair of cephalic eyes structurally similar to other lens eyes of gastropods. The second eye type is a lens eye that projects from the back of the animal."

To this layman it sounds like eyes in such different positions would make it more likely that they have independent heritage, but maybe some actual biologist will tell me that's likely not the case at all and that's not how that works.