Figure 2. Photos showing shell morphology of the two species land snails. The sampling strategy along with the growth band was also shown.
2.3 Ecological habits of the two species
The two species of land snails used in this study have different living habits. C. pulveratrix usually lives in relatively cold and dry climates whereas M. yantaiensis lives in warm and sub-humid climates (Wu et al. , 1996; Chen and Wu, 2008). The pictures for two species of land snails are shown in Figure 2. Both species are also living in the modern time. According to Chen (2016), C. pulveratrix distributes over a vast area including Shanxi, Henan, Hunan, Shaanxi, Gansu, Xinjiang provinces, and even in central Asia. The habitat for C. pulveratrix is usually in thick grasses or under the litter beneath trees in mountain area, on flat slope of hills as well as in ranches, orchards and crop land. M. yantaiensisdistributes usually in northern China, i.e., Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Shandong and Shaanxi, and also shows in area around the Yangtze River. It often lives in slightly damp bushes, grasses, under rocks and leaves in in mountainous and hilly areas.
Shell size comparion shows that C. pulveratrix is usually larger than M. yantainesis (Table 1). This morphology difference complies with their living environment conditions.According to previous studies, the large shell can reduce the ratio of surface area to volume, thereby limiting water evaporation and making it easier for the snails to survive in drier environments(Nevo et al., 1983; Yanes and Fernández-Lopez-de-Pablo, 2016).
Table 1 Snail shell sizes of the two species at various MIS stages.