As the animal grows, older pores aresuccessively filled in and closed. The number of open pores variesamong different abalone species. Shell exterior and interior colorvaries with species, but it is an unreliable form of identificationsince the color may not be clearly visible or the original descriptionmay not be accurateThe shell comprises three layers. The cuticle, which is the outerlayer, is an organic matter purely formed of concholin. It is verythin. The hard shell or middle layer(horny layer)is composedmainly of calcium carbonate crystals embedded in concholinwhose chemical components are similar to the one in cuticle layerThe innermost layer called pearl layer has chemical componentssimilar to the horny layerThe pearl layer is made of secretions occurring over the surface ofthe entire mantle. The cuticle and horny layers are secreted by themantle margin and the growth line appears on the edge of theshell. During the winter and spawning season, or under adverseenvironment conditions, no growth occurs, thus showing thegrowth stages and the physical condition of the abalone