In many marine creatures, however, the skeleton is composed of a mineral variety of calciumcarbonate called aragonite.
然而,很多海洋生物的骨骼由一种叫作霰石的碳酸钙矿物变体组成。
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The fossils buried in Pleistocene and earlier ocean sediments were of foraminifera—small, single-celled marine organisms that secrete shells of calciumcarbonate, or calcite.