The conflict between operative and conservative subsystems of organisms inthe evolution of terrestrial snails (Stylommatophora, Pulmonata)

In terrestrial snails a strategy of avoiding the unfavorable environmental influence and yet getting the needed information from the environment are r ealized by the existence of operative (shell) and conservative (cephalopodi um) subsystems. An increase of efficiency of the conservative subsystem man ifests itself in narrowing the aperture; intensification of the operative s ubsystem is displayed in increasing:the cephalopodium size.:The simultaneou s-activization of these subsystems is impossible since the large cephalopod ium cannot pass through the narrow aperture. This conflict is solved in the evolution of withdrawing systems directed at eliminating the relation aper ture diameter-cephalopodium size. That is probably a cause of the operculum loss, after which a basommatophoran pattern of withdrawal is formed, chara cteristic of aquatic mollusks and Succineidae family. Mollusks of Geophila order settle the conflict in two ways: by modification of basommatophoran w ithdrawal (Partulidae) and geophiloid withdrawal (from head to cephalopodiu m tail). In the lower Geophila the geophiloid withdrawal comes up against a natomic mechanisms of managing shells; the latter are replaced by concholog ical ones. However, the improvement of musculature results in a removal of contradictions and reduction of the apertual teeth. According to Iordansky (1990), these changes initiate the subsequent ones. The conflict of subsyst ems becomes aggravated again in transition to predatoriness because of the fast development of the cephalopodium. Some ways of resolving this conflict are considered.