green nature shell shells snail snails bleached cluster coiled shells colored coloured exoskeleton faded gastropods land snails metal fence post Molluscs slimy small spirally coiled shells terrestrial snails white aquatic beach Busycon carica coast dextral gastropod gastropod shell knobbed whelk marine marine gastropod molluscs migratory mollusk mollusks ocean sand sea Sea snail sea snails sea-snail seasnail Shell on the beach shore splash water wave welk whelk garden old slow gardening insect mollusc pest accident barren industrial oil oil spill oil tanker pollute pollution spill spillage bloom close-up detail flower macro mallow Malva pink slug snail shell calcium carbonate coiled crawling eye stalks eyes friction garden snail gastropoda helix aspersa herbivorous locomotion logarithmic spiral mantle movement mucus muscular foot olfactory organs ommatophores radula retractable retracting ripple rippling skin Slime spirally tentacles textured surface unsegmented