Almost all shells open on the right-hand side, with the exception of a few snail species whose shells open on the left. If you find a shell that opens on the left (as long as it’s from a normally right-hand species), you have a rare shell sometimes highly sought by collectors.

Gastropod shell

Most gastropod shells are spirally coiled. The majority (over 90%) of gastropod species have dextral (right-handed) shells, but a small minority of species and genera are virtually always sinistral (left-handed), and a very few species (for example Amphidromus perversus) show a mixture of dextral and sinistral individuals. There occur also aberrantly sinistral forms of dextral species and some of these are highly sought by shell collectors.

The left-handed turrid (Antiplanes vinosa)

If a coiled gastropod shell is held with the spire pointing upwards and the aperture more or less facing the observer, a dextral shell will have the aperture on the right-hand side, and a sinistral shell will have the aperture on the left-hand side…. Continue Reading (11 minute read)

12 thoughts on “Almost all shells open on the right-hand side, with the exception of a few snail species whose shells open on the left. If you find a shell that opens on the left (as long as it’s from a normally right-hand species), you have a rare shell sometimes highly sought by collectors.”

  1. Another interesting point: snails are only able to mate with snails with the same “handedness” as them. A right-hand snail cannot mate with a left-hand snail. (Their gametes are fine, but their genitals won’t line up.)

    This also means that snails have very unique evolutionary patterns, prone to speciation “jumps” triggered by the rare instance that two snails that are “wrong” for their species manage to find each other and mate. All of the offspring will be “opposite” from the original species and therefore incapable of finding a mate outside of their siblings, which pretty much turns them into a new species and magnifies the traits of the original pair.

    Another interesting fact is that snail-eating snakes often evolve specific adaptations for eating right-handed snails, but have a harder time with left-handed ones. It is possible that the reason why left-handed snail species survive despite their initial disadvantage is *because* they are less common – a kind of “sinister advantage” similar to the reason why most humans are right handed, but not all, applied to the entire species.

  2. [This reminds me of left-handed sugar](https://en.m.wikipedia.org/wiki/L-Glucose), which tastes exactly like sugar but is twisted the other way, we can’t process it into energy and it just passes through. The reason it didn’t catch-on, is the extreme cost of manufacturing.

  3. I remember back in 7th grade our teacher was giving a lesson on this, then she pulled out a left hand side shell, then about 4 more. We thought she was rolling in the money. Then she told us some species are left hand side.

  4. A small percentage of humans are also born with mirrored bodies. Their hearts are on the right, their livers are on the left, they’re usually left handed except for those that were “supposed” to be left handed, etc. Most people like this have no idea until they have to have some type of surgery

  5. Even more rare: a right handed shell for a left handed species. Most people will just assume its normal.

  6. Finally something to do with my research – chirality! This is the science of every structure that, when mirrored, results in a different, non-superimposable structure. Think of your right and left hands, for example, or these seashells. This becomes really interesting when dealing with biochemical chirality.

    For some mysterious reason, the handedness (i.e. which of the mirror images) of almost all natural compounds, such as DNA, amino acids and proteins, sugars etc., are almost always of a single direction, meaning you can find DNA helices that turn only in one direction, and proteins that have only one directionality for attaching to substrates (the mplecules on which they work, such as taking apart sugar for energy). No one knows what the rreason of this asymmetry is.

    Where this gets really important is with drug molecules, around half of which are chiral (have two distinct mirror images). Because the proteins that respond to these drugs are asynmetric, while one handedness can have useful effects and few side effects, the other can have no effect, really weak effects, or even be toxic! The most famous example of this is [thalidomide](https://en.m.wikipedia.org/wiki/Thalidomide#:~:text=Thalidomide%2C%20sold%20under%20the%20brand,conditions%20including%20complications%20of%20leprosy.), a drug that alleviates nausea and anxiety, so was naturally given to pregnant women back in the 50’s. Turns out, these effects are only true for one handedness, while the other causes severe mutations and birth defects in unborn babies… The story sadly ended with a few thousand dead babies, and tens of thousands born with horrible defects.

  7. Bookmarking for when I go to the beach at some point so I remember to find shells that open on the left

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