In some classifications, a subclass or superorder of the Chondrichthyes (cartilaginous fishes), containing the sharks. Their sharp teeth develop from the toothlike placoid scales (denticles) and are rapidly replaced as they wear out.
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。