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Monday, November 5, 2007

Exploding Shells

These snails, Alviniconcha hessleri are from hydrothermal vents at the Lau Back-Arc Basin (1800-2800m depth) where I am doing my PhD research. They are interesting for many reasons, one that they are chemoautotrophic with a highly reduced digestive tract and depend on endosymbiotic sulfide-oxidizing bacteria in its gills for the majority of its nutrition. They can get up to fist size and form dense aggregations of up to 100+ individuals in roughly 1/4 meter-squared. Research currently in review from a lab at UC-Santa Barbara has determined A. hessleri to have some serious fast metabolism and have the highest thermal-chemical tolerance of all the chemoautotrophic fauna at the Lau Basin vents. It a very interesting mollusc and a very beautiful one too. Below is a picture of an air-dried one that last several months before peeling away. It was taken by my wife, who is a photographer.

Notice their thin shell and spiny periostracum. The periostracum is an organic layer laid down over the calcareous layer of the shell. For more information about Alviniconcha, I wrote an article on this species when I was writing for Deep Sea News. Below, you'll see pictures of what happens to the shells after time takes it's toll. Pictures taken by myself (obviously not a photographer) in a box I put them in to dry. This was about 2 days after 3 hour and 24 hour mineral oil treatments.

My question to the malacologically-inclined community is this: any suggestions for dry preservation of rare deep-sea shells? No matter what I try, they end up blowing up. I've tried letting them dry out in the open air, dry out in a drying oven (60C), spraying them bumloads of shellac (which just slows down the time to kaboom), and drowning them in mineral for a few hours to a day (see last pictures for the outcome). Using a drying oven, I heard a pop after 30-60 minutes and found shell fragments and periostracum spines all over the mussel body tissue I had in there for condition analyses. Drying in the open air results in a slow (over the course of a few weeks) peeling back of the aperature until the tension breaks the shell. Shellac only works for a couple months and mineral oil not at all. I have another shell in mineral oil for a week now so I'll take it out and drain it and see if it explodes too.

Any suggestions are welcome. I'm sure there are some shell collectors among my readership. I only have about 20-30 shells left so I don't want to experiment too much further. They are left over from failing to reject a certain null hypothesis of mine. I will blog on that later, even with data! It all boils down to 1.5 years of work relegated to a sentence in the materials and methods and maybe a couple in the discussion.


  1. Any idea of the function of the spiny periostracum? Do other gastropods have anything similar? Do they come up clean like this, or covered in futz? Seems like those spines would trap a lot of floc.

  2. The problem here is the nature of the two different materials. The periostracum is made of chitin, perhaps with some proteins mixed in. The shell of course is calcium carbonate. The chitin must be contracting as it dries. Unless you can find something to complex with the chitin in order to keep it from shrinking, a dry shell will be hopeless. My guess is you will have to keep the thing wet or embed it in plastic. I wonder if there might be some information in the chitin extraction and use literature?

  3. Kevin, have you tried glycerol? I remember reading about the same problem in some land snails. You may want to post the question at CONCH-L ( and/or at Mollusca ( You have to subscribe to each list fist, though. If you want, I can ask the question for you.

  4. Jason, I totally write a nice long reply yesterday and must hit cancel instead of send. doh! I'll try to be as thorough as I was previously.

    Yes other gastropods do have spiny periostracum. Though the spines are arranged along the longitudinal ribs of the calcareous shell, they are purely from periostracum and not covered calcareous spines unlike some other marine gastropods. I remember Aydin posting about spiny terrestrial snails. Maybe he can come through with the link.

    There is no conclusion about the function of the spines, they do not generally accumulate flock, BUT in some snail beds they ca be covered with a white layer, which is a bacterial mat. My own research has found very strong correlations of the vent crab Austinograea spp. with this snail. They don't seem to prey upon the snail, although when we crushed several during collection, they all seemed to pour out of nowhere and converge on the collection ring! So maybe they opportunistically take a snippet here and there. With that being said, they may feeding off the bacteria grown on the snail's shells. I'll have to do an analysis comparing densities of crabs on snails with and without bacterial mats. My first pet hypothesis was that the spines evolved to keep off fouling limpets that can drill through shells. Alviniconcha's shell is very thin, so there may be a trade-off between shell thickness and spiny periostracum synthesis. The periostracum does erode from the apex down as they get larger.

  5. Hi Dr. Watling! Thanks for stopping by and commenting, its an honor. I wonder if deep-sea shells' chitin is more prone to contraction due to the fact it was under pressure when synthesized. The decrease in pressure to atmospheric might make it contract? I'll have to check into the chitin literature more (but after my comps in 2 weeks!).

  6. Aydin, i just got some emails suggesting a mixture of 50/50 glycerin/alcohol for a week or 2 and then stepping the glycerin up gradually. I'll give it the ole college try on a couple shells. I also have a shell still sitting in mineral oil. I might have pulled the others out prematurely, before it had time to cure and set in. This person noted new zealand terrestrial snails that behave exactly like mine, so it might not be a pressure issue after all.

    I'm a subscriber to both lists, so if glycerin doesn't work I'll pose the question to the list.

  7. have your tried a staple gun to attach the periostracum to the shell?

  8. I have written a few times about land snails with hairs. This is one of those posts.


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