Gastropods without torsion in development

[pinkunicorn]

en.m.wikipedia.org/wiki/Torsion_(gastropod)

Torsion is why your snails and slugs poops from their anterior ends instead of posterior ends.

But I got curious about species that poop from their posterior ends, aka species that apparently don't have torsion phase. I bought some lovely leatherleaf slugs, Laevicaulis alte, which poop from their backsides. They also have contractile as opposed to retractile tentacles and other really funny unusual slug traits. I've not yet seen any mating behaviour but I can't wait to see if it also happens differently!

These "little pancakes" or "poffertjes" as I call them got me thinking what other gastropod families do not go through this development phase, and thus have "abnormal" gastropod features as described above? L.alte is of the Veronicellidae-family, which includes the Pancake slug of Jamaica and "the velvet slug" that is often sold as "Laevicaulis sp." so possibly other Veronicellidae also don't.

Does anyone know any others? Perhaps even keep them as pets? Have you seen them mating, and how do they do it?

Edit: I'm mistaken I think... it says it happens in all gastropods but some reverse back to the original position. Bizarre. Anyway, the question remains: does anyone know more of the gastropods that have their posterior and anterior sides at the opposite ends of body?

[latebloomer]

I find the evolution of gastropods fascinating, but have not found as much information as I would like (not wonderful with with internet searching ) If torsion developed as an evolutionary strategy to accomodate developing a different shell for protection for moving onto land from the sea, might slugs, who have evolved away from shells, eventually evolve away from torsion? Interesting.

[pinkunicorn]

Most land slugs do poop from under the mantle like snails would without a shell. But the Veronicellids are really weird in the sense that they're basically all mantle and very little slug whilst most slugs have a very small mantle! Plus they are described as "primitive" which makes the evolutionary order even more perplexing. Or maybe gastropods are going both ways: no shell, shell, no shell again, shell again. I wonder if there's any semi-slugs that have a growing shell? (By population, not by individual of course)