close-up closeup garden snail land snail landsnail snail bleached cluster coiled shells colored coloured exoskeleton faded gastropods land snails metal fence post Molluscs slimy small snails spirally coiled shells terrestrial snails white gastropod herbivore land shell slug calcium carbonate coiled crawling eye stalks eyes friction gastropoda helix aspersa herbivorous locomotion logarithmic spiral mantle mollusk movement mucus muscular foot olfactory organs ommatophores radula retractable retracting ripple rippling skin Slime spirally tentacles textured surface unsegmented animal beige brown grass green grey l gravel nature sand soi spring summer gravel Soil spiral