University of Education, 390000 Ryazan, 46 Svobody str.

Abstract

Most snails dwelling in wet microhabitats (lower layers of fallen leaves, wet screes etc.)are relatively small. They have problems of locomotion because of the complexity of theirhabitats and particularly because of water gripping the shell through surface tension.I recognize four adaptations to these conditions: 1) water repellent conchioline hairs on theshell surface (some Helicoidea, Polygyridae); 2) apertural teeth that facilitate control of theshell's position (some Helicoidea and Endodontinae); 3) fusion of three branches of thecolumellar muscle into one, so that it is hard enough to drag the shells through the obstacles(Zonitinia, Oreohelix); 4) shell loss leading to appearance of the slugs. The second and thefourth mechanisms evolve probably through a positive feedback mechanism operatingbetween morphology and environment.