Surprise surprise! Sometimes I find a photo and do not expect a story behind, but then this happens:
This leatherleaf slug has some really interesting features. It doesn’t look like a common slug obviously, because the whole body is more flat than usual. But the real surprises lie somewhere hidden. We have a member of the family Veronicellidae, order Systellommatophora. The more common snails, like the Giant Landsnail, are all found in the order Stylommatophora.
L. alte grows up to 6.5 cm and 4 grams. This species was introduced from Africa to many regions, and seems to like plants we also like, either to eat, watch, or smoke. So it is yet another alien, and crop eater. In Singapore you see them from time to time, but you’ll see 20 African Landsnails before you see one Leatherleaf. They are not shy, usually they won’t run away as you get closer.
Their anatomy is different from the more common slugs, and that’s a story!
1. The foot: Usually we see a slug from the top, as long as it’s not climbing a window. If we could see this slug from below, we would see that it’s a real little foot! The foot is very narrow, maybe 5mm only, like they were a monorail! They do that to reduce evaporation, so these slugs are more suitable for dry areas.
2. They have things in place, I mean they have it where we would say it belongs. What I wasn’t aware is, that slugs of the order Stylommatophora have their anus where I would say is their shoulder, so somewhere behind the head. Our slug for a change has it where we would put it, in the very back. Nice move Systellommatophora! They also don’t have a lung, like the normal slugs, but that’s rather unspectacular, isn’t it? The genitals were placed in both orders in the center of the slug. Learn more here!
I wondered how the anus ended up in the middle of slugs, maybe you do too. The answer is torsion. All snails and slugs do this during their development in their egg. Torsion means twisting, and if I got that right, more or less the whole belly twists against head and foot. Like you would rotate your torso by 180 degrees, have fun picturing that.
The reason for this torsion in the gastropods is not 100% clear. It comes with benefits as well as with challenges, but I like the conclusion that it can’t be too bad, since we have snails everywhere. It works for them! The benefits might be more for the snails, whom are able to get their head into their house, since the entrance is rotating to the front during that torsion.
So when I say all snails do that, how come our member of the Systellommatophora isn’t twisted? They are, but they decided to twist back – detorsion! Interesting is, that they have to re-twist, instead of just skipping that step. Anyhow, our monorail has the exit in the back.
Last thing, a slug is not to cuddle, though they look cute and kind. There are nematods, tiny worm like creatures, that live in the slugs (the rat lungworm Angiostrongylus cantonensis), and these worms cause Eosinophilic meningitis. So stay strong and don’t touch them!
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