per.i.os.tra.cum
n.（名词）【复数】 per.i.os.tra.ca[-k…] The hard chitinous outer covering of the shell of many mollusks, especially freshwater ones, that protects the shell from the erosive action of water.角质层：许多软体动物，尤指淡水软体动物身体硬壳外包的一层物质，用以防止壳受水的侵蚀作用
来源：New Latin 现代拉丁语 peri- peri-Greek ostrakon [shell] * see ostracod 希腊语 ostrakon [壳] *参见 ostracod
