shell, and adds to the shell to increase its size and strength as the animal grows. Shell material is secreted by the 外胚层ic (上皮组织) 细胞 of the mantle tissue.
腹足纲物种的外套膜.不少腹足纲物种的外套膜都藏在其螺壳里。以下图片为一些例子：In species where the shell is small compared