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

摘要

In terrestrial snails a strategy of avoiding the unfavorable environmental influence and yet getting the needed information from the environment are realized by the existence of operative (shell) and conservative (cephalopodium) subsystems. An increase of efficiency of the conservative subsystem manifests itself in narrowing the aperture; intensification of the operative subsystem is displayed in increasing the cephalopodium size. The simultaneous activization of these subsystems is impossible since the large cephalopodium cannot pass through the narrow aperture. This conflict is solved in the evolution of withdrawing systems directed at eliminating the relation aperture diameter -- cephalopodium size. That is probably a cause of the operculum loss, after which a basommatophoran pattern of withdrawal is formed, characteristic of aquatic mollusks and Succineidae family. Mollusks of. Geophila order settle the conflict in two ways: by modification of basommatophoran withdrawal (Partulidae) and geophiloid withdrawal (from head to cephalopodium tail). In the lower Geophila the geophiloid withdrawal comes up against anatomic mechanisms of managing shells; the latter are replaced by conchological 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 subsystems becomes aggravated again in transition to predatoriness because of the fast development of the cephalopodium. Some ways of resolving this conflict are considered.