chitin India krayker limpets macro malacology mantle mantle cavity Marine organism mollusc Mollusca Molluscs mollusk mother of pearl plates shell shells spicules spiral Spirally-coiled shells background cream dip Dirt dust dusty edge pearly pitted ridge ridges rim rough seashell sharp smooth spiraling spiralling surface texture textures turban shell turns twists beach natural nature ocean sea water backgrounds brown colors colours edges folds layers seashells shape shapes Sizes textured types variety white golden shell orange rock sea shells shells on the rock spiral shell black