Science. 1993 Oct 1;262(5130):93-4. doi: 10.1126/science.262.5130.93.
Phosphatized univalves, recovered from the Lower Cambrian ( approximately 530 million years old) Qiongzhusi Formation in southern China, are recognized as early instars belonging to bradoriid ostracodes whose later instars are bivalved. The univalved form is the primitive larval character for shell-secreting crustaceans, although most post-Cambrian ostracodes bypassed this developmental phase. The univalved-bivalved transition during early on-togeny represents an important evolutionary event in ostracodes, with implications for crustacean classification, and implies that the ostracode ancestor achieved this bivalved capacity before the appearance of mineralized skeletons during the "Cambrian explosion."
在中国南方下寒武统（约 5.3 亿年前）琼枝山组中发现的磷化单壳类，被认为是属于 bradoriid 介形类的早期幼虫期，其后期幼虫期为双壳类。单壳类是具有壳的甲壳类动物的原始幼虫特征，尽管大多数后寒武纪介形类动物都跳过了这个发育阶段。在个体发育早期，从单壳类到双壳类的过渡是介形类动物的一个重要进化事件，对甲壳类动物的分类具有重要意义，并且表明介形类动物的祖先在“寒武纪大爆发”期间出现矿化骨骼之前就已经具备了这种双壳类的能力。
