Mark Wilson March 14th, 2012
MITZPE RAMON, ISRAEL–This exquisite snail is not a fossil, although students in the field often mistake it for one. (Melissa did not, I quickly add.) It is a terrestrial, air-breathing pulmonate snail called Sphincterochila boissieri. It is abundant in parts of the Negev and the Sinai Peninsula. Its shell is relatively thick for a land-dwelling mollusk, so it becomes a common constituent of the desert soil in certain habitats.
Sphincterochila boissieri is well adapted to its desert environment. It has a predator-resistant shell with a small aperture to reduce moisture loss. With its white color it reflects significant amounts of solar energy, staying relatively cool. (Compare this to the black ground beetle in the last post. It is most active in the winter and stays in shady areas during the summer.) They are active for only a few days during the winter rainy season, doing all their feeding (on algae, moss and lichens), mating and egg-laying. For the rest of the year they stay dormant, often in the soil or attached to rocks and woody plants. While dormant, they pull all the way back into the second and third whorls of their shell to stay as moist as possible. They can survive droughts, and thus do no feeding, for at least six years.
So, S. boissieri may not be one of our fossil targets, but it is a silent (and completely unmoving) companion during our fieldwork. It has our respect!
Yom-Tov Y. 1971. The biology of two desert snails Trochoidea (Xerocrassa) seetzeni and Sphincterochila boissieri. Israel Journal of Zoology 20: 231-248.
Shachak M., Chapman E.A. and Orr Y. 1976. Some aspects of the ecology of the desert snail Sphincterochila boissieri in relation to water and energy flow. Israel Journal of Medical Science 12: 887-891.