Calcium carbonate constitutes the shells of molluscs, brachiopods and some tube-building polychaete worms and silica forms the exoskeleton of the microscopic diatoms and radiolaria.
kˈælsiəm kˈɑːɹbənˌeɪt kˈɑːnstɪtˌuːts ðə ʃˈɛlz ʌv mˈɑːlʌsks, bɹˈækɪəpˌɑːdz ænd sˌʌm tˈuːbbˈɪldɪŋ pˌɑːlɪkˈiːt wˈɜːmz ænd sˈɪlɪkə fˈɔːɹmz ðɪ ˈɛksoʊskˌɛlᵻtən ʌvðə mˌaɪkɹəskˈɑːpɪk dˈaɪəɾəmz ænd ɹˌeɪdɪoʊlˈɛɹiə.