Trying to find out the name of this little sea creature was one of the most vexing internet searches I’ve ever performed, each likely search term taking me into some scary world of decorative objects involving seashells. Take my word. Never. Ever. Put the word “decorative” into a search engine. Even “spiral stone pattern on seashell” threw up images of crochet, jewelry, fractals, land-art and so on. C’mon Internet! I want to know the name of this mollusc and why it finds and sticks these little pieces of rock on the outside of its shell!
“stones stuck to seashell”
“stones stuck on seashell”
=( I’ll spare you.
“stones in spiral pattern on seashell”
=( Sometimes it’s best to not try to pre-empt.
=( “what seashells stick stones on their shells?”
=( Even http://www.seashells.org – a site that claims to be devoted to the answering of all my questions I might have about seashells, was useless. I did learn from Wikipedia however that my shells belong to the class Gastropoda which has about 60,000–80,000 species, second only to insects in their diversity. I latched onto periwinkle too early. “decorated periwinkle shell”
• • •
Almost there. It’s not a lending library.
And here it is! OK. Superfamily: Xenophoroidea. ….. virtually all species attach foreign materials to the shell surface, particularly at the periphery of the last whorl, a habit apparently developed to help the mollusc escape detection. … Family: Xenophoridae. My shells are Xenophora (Stellaria) chinensis, also known as carrier shells because of this habit of carrying around stuff.
The name Xenophora comes from two ancient Greek words, and means “bearing foreigners”, so-called because in most species the snail cements pieces of rock or shells to its own shell at regular intervals as the shell grows. Although the foreign objects are usually such things as gastropod or bivalve shells, pebbles, or small pieces of coral rock, in some instances a bottle cap has been attached by the snail to its shell.
By the time I see them, any stuff around the lowest whorl has gone. I’ve also never seen one with only shell or only stones added. The ones I see all seem to have a mix of the two, even though the layout is random. I don’t buy the camouflage thing. Take a look at some the more spectacular examples of Xenophora from this site.
Some, Nos. 3 & 8 for example, actually do look like something else. No. 5 too is a bit excessive but I can see how it might work as camouflage.
- With my guys, I think there might be something more going on because these shells are incredibly easy to spot. Regular patterns of regularly spaced and regularly sized stuff don’t make for great camouflage. If they’re hiding from predators, then it’s not by confusing their sense of sight. Also, you would have to be certain you’re not cladding your shell with the shells of something even more delicious. This could be why empty bivalve shells are always stuck on with the concave surface facing outwards. (“Move on, nothing to eat here!”)
- However, the more I think of it, I think my guys go beyond the defensive. If the shells were just visual or tactile camouflage, then I’d expect to see less of the insides and more of the outsides of half-shells since that’s more likely to replicate the action on the deep-sea floor and not the beach where all the dead stuff washes up. Instead, bivalve shells are almost always attached with the inside facing out. It’s not camouflage.
- Moreover, the foreign stuff isn’t just attached, it’s embedded. There are convex impressions on the interior. Sometimes you even see a hole in the shell where a sliver of rock or shell has been dislodged when being washed up. These rocks and shells aren’t decorative – they are the surface. We’re talking thin-shell structures.
- Whether shell or stone is used, the goal seems to be to make the finished surface as flat as possible. This is incompatible with visual or tactile camouflage but, if the more convex surface faces in, is compatible with lessening the quantity of “cement”.
I think these clever gastropods are using the foreign matter as aggregate to strengthen their shells and at the same time use less of whatever it is they secrete to make the shell itself. If so then that’s pretty clever. The combination of geometry, structural reinforcement and ad-hoc salvaged cladding is a good one. I hope these creatures gain some evolutionary advantage out of all the time, energy and resources they so brilliantly save. They’re onto something.
The first of these shells I ever saw instantly reminded me of this collage by Matisse and which, Matisse being Matisse, is trying to be beautiful.
Xenophora chinensis have never seen The Snail but Matisse did make several trips to North Africa between 1906 and 1913 and spent seven months in Morocco 1912–1913 so it’s not unlikely he came across one on the beach much as I did. It’s not unlikely that in 1953, bedridden, he remembered this collaged shell he saw in Morocco forty years earlier and decided to make his own. He was an artist, after all.
Architects however, have other lessons to learn and one of them is that beautiful things sometimes result from not pursuing beauty but from pursuing other things such as structural integrity, the re-use of available materials and the prudent use of new ones.
The misfit molluscs are not trying to look beautiful.