The thin layer of leather silt on the back of its body and
periostracum prevents the dissipation of water inside by the
irradiation of sunlight, and keeps the body humid. The extent of
movement is correlated with RH. Peak RH appears at dawn when the
temperature is lowest, with the minimum always in the afternoon
when the temperature is highest. Thereafter, RH gradually increases
with the decrease of air temperature. The higher the RH, the less water
evaporates on the surface of the body. When air temperature reduces,
RH grows to 100%. If the weather continues to be cold, the vapour will
coagulate into liquid and then change into dew. Moving out at night
can reduce the loss of water on the surface of the body. So Onchidium
usually move at night or after rain. This habit is different from most
Gastropoda because of its living circumstance. This characteristic is
also an important adaptation to terrestrial life (Li Yongcai and Huang
Yiming, 1984).