Influence of moisture on growth and egg production by Subulina octona(Bruguiere) (Mollusca, Subulinidae), reared in different substrates, under laboratorial conditions

The aim of this study was to observe the influence of substrate moisture on growth, number of eggs produced and shell length of Subulina octona (Bruguiere, 1789) in its first reproductive event. For this, two groups of moluscs were observed under laboratorial conditions. The trated group, manteined in substrate moinstened at five-days intervals and the control group, manteined in substrate moistened at one-day intervals, were both constituted by 210 newly hatched individuals distributed in boxes with different substrates. The box one and control one contained sand, the box two and control two, clay and the box three and control three, humus. Each box contained 35 snails. The individuals of the control group exhibited a faster growth rhythm than those of the trated group. The substrate moisture was a major influence over the individuals reared in sand and clay. It's probable due to the fact that these substrates loose water by evaporation more quickly than humus. The land snails loose water by their skin and by the same means they rehidrate by contact. So, the humidity of the substrate on wich the snails live influence their homeostasis. Substrates that retain water for a smaler time period offer fewer oportunities to rehidration. The waterloos by the skin, without later rehidration can causes changes in hemolinph osmolarity, with implications over the feedind control, hearth beating and locomotion. By this way, snails submited to dessication exhibes reduced activity and consequently smaler growth and produtivity.