Sphincterochila boissieri

Sphincterochila boissieri lives in desert environments. This snail is common in areas with loess-limestone soils, and uncommon in areas that have a flint substrate.[8]

Yom-Tov measured the maximum demographic density for Sphincterochila boissieri, encountering a value of 0.2-0.3 specimens/m² in the area of the Negev desert he investigated in 1970.[5] The snail Xerocrassa seetzeni was found to be more abundant there. On the other hand, in the Northern Negev area investigated by Steinberger et al. In 1981[9] Sphincterochila boissieri was the most abundant snail.[6]

Sphincterochila boissieri along with other snail species and algae are the most significant faunal and floral components of the Negev and Sinai deserts ecosystems.[6]

Sphincterochila boissieri in Hamakhtesh Hagadol, northern Negev. Diameter is 2.1 cm.

Sphincterochila boissieri shells below a limestone wall in Hamakhtesh Hagadol, northern Negev.

This species presents adaptations to arid conditions which significantly improve its desiccation tolerance. Some of those adaptations include a thick shell and a relatively reduced aperture[10] (see also Machin 1967), a thick epiphragm, and slow body surface heat conduction. About 90% of its shell surface reflects the visible portion of the solar spectrum, and much over 90% of the solar spectrum itself.[8] Sphincterochila boissieri also produces a new epiphragm after every period of activity[11] (see also Yom-Tov 1971).

These snails dig themselves into the soil to depths from 1 to 5 cm while they aestivate during summer in the Negev Desert.[5] In the vicinity of the Dead Sea, they usually either burrow to depths of up to 10 cm, or aestivate hidden under stones.[8]

All dormant snails of this species can resist ambient temperatures up to 50 °C, but temperatures of 55 °C and above are usually lethal.[8] The soft parts of the animal's body shelter inside the second and the third whorl of its shell, where the temperature can reach up to 50.3 °C. Temperatures of up to 56.2 °C were measured and are known to occur inside the shell's body whorl, which is mostly filled with air during aestivation.[8]

Dormant snails experience water loss of 0.5 mg per day per snail in summer, with a very low oxygen consumption rate.[8] For these reasons, dormant Sphincterochila boissieri can survive severe droughts for several years.[8][12]

Sphincterochila boissieri is active for a few days only after rainfall[6] during the winter season, from November to March. At this time of the year they feed, mate,[8] and lay eggs.[6] Thus these snails are active for only 5-7% of the year (nearly 18 to 26 days), and aestivate during all the rest of the time.[6]

Dormant snails are known to have survived in museum collections for up to 6 years.[8] Schmidt-Nielsen et al. in 1971[8] estimated their life span according to their oxygen consumption as being nearly 8 years.

Sphincterochila boissieri feeds on soil, especially loess mud after rains,[8] lichens, soil algae[5] and surface of limestone directly.[8] It does not eat higher plants.[8]

The known predators of Sphincterochila boissieri are rodents, namely the Cairo Spiny Mouse (Acomys cahirinus), Wagner's Gerbil (Dipodillus dasyurus) and the Asian Garden Dormouse (Eliomys melanurus).[5]