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January 19, 2008

World's only four-axis snail

Hbouhnou

Look at the photo above.

What do you see?

No, it's not a creature from a David Cronenberg movie but, rather, a newly discovered species of snail called Opisthostoma vermiculum, whose shell (above) is about 1 millimeter long.

Henry Fountain wrote about it as follows in the January 15, 2008 New York Times Science section.

    Shell of New Species of Land Snail Coils Its Own Way

    It looks like the plumbing on a rocket engine, or perhaps an alpenhorn gone wild. But the oddly coiled tube pictured here (at great magnification) is actually the shell of a land snail.

    "I thought it was one of mother nature's practical jokes,"€ said Reuben Clements of the World Wide Fund for Nature in Selangor, Malaysia, who found the shell and dozens more just like it in a limestone outcropping in central peninsular Malaysia.

    The shells, which are about one twenty-fifth of an inch long, belong to a new species of snail, Opisthostoma vermiculum, which Mr. Clements and colleagues describe in the journal Biology Letters. Because of the collection technique, none of the actual snails survived; so nothing is known about them, although it is presumed that they eat detritus like other small land snails.

    But the shells are remarkable. While the typical snail shell coils tightly around a single axis, attaching to itself as it spirals outward, O. vermiculum coils much more loosely, twisting and turning and reattaching only in spots.

    Other loose-coiling land snails are known, but O. vermiculum surpasses them in one respect. It coils around four distinct axes, shown by the white lines in the image. That is one more than any other known snail.

    Mr. Clements said O. vermiculum was found in only a single outcropping in a karst region — an area of limestone hills and caves formed by erosion of ancient marine sediments. He is studying the karst fauna with a view to protecting it from quarrying and other industrial activity.

    As to why the snail forms such a distinctive shell, Mr. Clements suggested that perhaps the odd shape helped with flotation, increasing the snail's survival chances in wet conditions.

    But that is just speculation. "I'm hoping to observe them in the wild,"€ Mr. Clements said. "But these are really tiny snails, and they're a challenge to find."

....................

Here's a link to the abstract of the Biology Letters paper, published online on January 8, 2008; the abstract itself follows.

    Further Twists in Gastropod Shell Evolution

    The manner in which a gastropod shell coils has long intrigued laypersons and scientists alike. In evolutionary biology, gastropod shells are among the best-studied palaeontological and neontological objects. A gastropod shell generally exhibits logarithmic spiral growth, right-handedness and coils tightly around a single axis. Atypical shell-coiling patterns (e.g. sinistroid growth, uncoiled whorls and multiple coiling axes), however, continue to be uncovered in nature. Here, we report another coiling strategy that is not only puzzling from an evolutionary perspective, but also hitherto unknown among shelled gastropods. The terrestrial gastropod Opisthostoma vermiculum sp. nov. generates a shell with: (i) four discernable coiling axes, (ii) body whorls that thrice detach and twice reattach to preceding whorls without any reference support, and (iii) detached whorls that coil around three secondary axes in addition to their primary teleoconch axis. As the coiling strategies of individuals were found to be generally consistent throughout, this species appears to possess an unorthodox but rigorously defined set of developmental instructions. Although the evolutionary origins of O. vermiculum and its shell's functional significance can be elucidated only once fossil intermediates and live individuals are found, its bewildering morphology suggests that we still lack an understanding of relationships between form and function in certain taxonomic groups.

January 19, 2008 at 04:01 PM | Permalink


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