A group of early Palaeozoic animals with calcareous exoskeletons, interpreted by some as carpoid echinoderms (Echinodermata), and by others as ancestors of the Chordata.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。